Sheep Veterinary Practice 9781032382883, 9781032382838, 9781003344346

Table of contents :
Cover
Half Title
Title
Copyright
Contents
Preface
About the Editor
List of Contributors
List of Abbreviations
Chapter 1 Veterinary Services to Sheep Farms
1.1 The Role of the Veterinary Practitioner in the Australian Sheep Industry
1.1.1 The Levels of Sheep Veterinary Services
1.1.2 To Move from Generalist Practice to a Higher Level of Service
1.1.3 To Move from Level 2 Services to Level 3 Services
1.2 Important Industry Knowledge—The Elements of a Sheep Production System
1.2.1 Breed, Genotype and Genetic Merit
1.2.2 Production Objectives
1.2.3 Flock Structure
1.2.4 Stocking Rate
1.2.5 Farm Management Calendars
1.2.6 The Business Aspects of Sheep Farming
1.3 Investigations of Disease or Poor Performance in a Sheep Flock
1.3.1 Structure of the Investigation
1.4 Developing a Flock Health Programme
1.4.1 The Reasons for a Flock Health Programme
1.4.2 Delivery of the Programme
1.5 Body Condition Scoring and Its Relationship to Productivity
1.5.1 Usefulness of Body Condition Scoring
1.5.2 Reliability of the Technique
1.5.3 Relationship of Body Condition Score to Health and Productivity
1.5.4 Relationship of Body Condition Score to Welfare
1.5.5 The Use of Body Condition Score Targets
Recommended Reading
References
Chapter 2 Welfare of Sheep
2.1 Concepts of Animal Welfare
2.1.1 What Is Animal Welfare?
2.1.2 Sentience
2.2 Sheep Behaviour and Sociability
2.2.1 Social and Predator Avoidance Behaviour
2.2.2 Abnormal Behaviours
2.2.3 Sheep Cognition
2.2.4 Learning
2.3 Sheep–Handler Interactions
2.3.1 Behavioural Handling Concepts
2.3.2 Handling Approaches and Yard Design
2.3.3 Sheep Neglect and Undernutrition
2.4 Husbandry Procedures and Alleviation of Pain
2.4.1 Tail Docking
2.4.2 Castration
2.4.3 Mulesing
2.4.4 Horn Trimming and Dehorning
2.4.5 Assisted Reproduction Procedures
2.5 Thermal Comfort
2.5.1 Heat Stress
2.5.2 Cold Stress
2.6 Welfare Impacts of Key Disease Conditions
2.6.1 Footrot
2.6.2 Mastitis
2.6.3 Lambing Losses
2.6.4 Flystrike
2.7 Humane Killing Techniques and Considerations
2.7.1 Anaesthetic Overdose
2.7.2 Gunshot
2.7.3 Captive Bolt Devices
2.7.4 Neonatal Lambs
2.7.5 Assessing Insensibility
2.7.6 Secondary Killing Methods
2.7.7 Inhumane Methods
2.7.8 Confirming Death
2.7.9 Further Resources on Humane Killing
2.8 Assessment of Sheep following Bushfires
2.9 Welfare Monitoring and Record Keeping
2.10 Conclusions
References
Chapter 3 Energy and Protein Nutrition of Grazing Sheep
3.1 Introduction
3.2 Energy and Protein Requirements of Grazing Sheep
3.2.1 Ruminant Digestion
3.2.2 Estimating the Energy Requirements of Grazing Sheep
3.2.3 Maintenance Energy Requirement of Penned Sheep
3.2.4 Maintenance Energy Requirement of Actively Grazing Sheep
3.2.5 Maintenance Energy Requirements of Cold-Stressed Sheep
3.2.6 Metabolisable Energy Requirements for Gestation
3.2.7 Metabolisable Energy Requirements for Lactation
3.2.8 Guidelines for Managing Pregnant Ewes to Ensure High Rates of Lamb Survival and Lamb Growth to Weaning
3.2.9 Metabolisable Energy Requirements for Growing Weaners
3.2.10 Protein Requirements of Grazing Sheep
3.2.11 Nutrition and Wool Growth
3.3 Nutrition and Management of Grazing Sheep for Good Health and Production
3.3.1 Nutrient Supply from Pastures in Mediterranean and Cool Temperate Climates
3.3.2 Matching Energy Demand with Energy Supply from Pastures
3.3.3 Relative Feeding Value of Legumes versus Grasses
3.3.4 Why Do Legumes Support Higher Levels of Animal Production than Grasses?
3.3.5 Nutrient Supply from Pastures in Subtropical Climates
3.3.6 Feeding Behaviour of Grazing Animals
3.3.7 Grazing and Pasture Management for Sheep Production
3.3.8 Pasture Growth Rate and Phases of Plant Growth
3.3.9 Relationships between Herbage Mass, Nutritive Value of Pasture and Energy Intake in Sheep
3.3.10 Effect of Diet Selection on Pasture Growth
3.3.11 Grazing Management to Optimise Sheep Production per Hectare
3.3.12 Stocking Rate, Stocking Density, Dry Sheep Equivalent and Sheep Production
3.4 Estimating the Digestibility and Total Quantity of Feed on Offer in Grazed Pastures
3.4.1 Assessing Herbage Mass (Or Feed on Offer) in Pastures
3.5 Supplementation of Grazing Sheep
3.5.1 Cost of Supplements
3.5.2 Deciding the Level of Supplementation
3.6 Deleterious Compounds Found in Common Pasture Forages and Invasive Weeds of Pastures
3.7 Recommended Additional Resources
3.7.1 Decision Making in Grazing Sheep Enterprises
3.7.2 Drought Feeding Guide
References
Chapter 4 Clinical Aspects of Trace Element and Vitamin Nutrition
4.1 Copper (Cu)
4.1.1 Physiology
4.1.2 Dietary Sources of Copper
4.1.3 Clinical Signs of Copper Deficiency
4.1.4 Subclinical Copper Deficiency
4.1.5 Seasonal Variations in Copper Availability
4.1.6 Clinical Pathology and Confirmation of Deficiency
4.1.7 Treatment and Prevention of Deficiency
4.2 Cobalt and Vitamin B12
4.2.1 Physiology
4.2.2 Dietary Sources of Cobalt
4.2.3 Pathophysiology of Cobalt Deficiency
4.2.4 Clinical and Subclinical Outcomes of Deficiency
4.2.5 Clinical Pathology and Confirmation of Deficiency
4.2.6 Treatment and Prevention of Deficiency
4.3 Selenium
4.3.1 Introduction
4.3.2 Physiology
4.3.3 Dietary Requirements for Selenium
4.3.4 Seasonal Variation in Selenium Nutrition
4.3.5 Signs of Selenium Deficiency
4.3.6 Subclinical Deficiency of Selenium
4.3.7 Clinical Pathology and Confirmation of Deficiency
4.3.8 Necropsy Findings
4.3.9 Treatment and Prevention of Deficiency
4.3.10 Selenium Toxicity
4.4 Vitamin E Deficiency
4.4.1 Introduction
4.4.2 Dietary Sources and Requirements of Vitamin E
4.4.3 Clinical and Necropsy Signs of Vitamin E Deficiency
4.4.4 Subclinical Deficiency of Vitamin E
4.4.5 Clinical Pathology and Confirmation of Deficiency
4.4.6 Treatment and Prevention of Deficiency
4.5 Differential Diagnosis of Myopathy
4.6 Iodine Deficiency (Including Goitre and Hypothyroidism)
4.6.1 Introduction
4.6.2 Goitrogens
4.6.3 Hypothyroidism Due to Inadequate Dietary Iodine
4.6.4 Inherited Hypothyroidism and Congenital Goitre
4.6.5 Hypothyroidism Due to the Ingestion of Goitrogens
4.6.6 Development of Hypothyroidism
4.6.7 Effects of Foetal Hypothyroidism
4.6.8 Clinical Signs of Iodine Deficiency
4.6.9 Diagnosis of Iodine Deficiency
4.6.10 Treatment and Prevention of Deficiency
4.7 Iron Nutrition
4.8 Molybdenum Nutrition
4.9 Manganese Nutrition
4.10 Zinc Nutrition
4.11 Investigation of Micronutrient Deficiencies
4.11.1 Clinical Pathology
4.11.2 Response Trials
4.12 Broad-Spectrum Supplementation
4.12.1 Licks and Blocks
4.12.2 Mineral Supplements for Oral Dosing and Risks of Mixing Products
Recommended Reading
References
Chapter 5 Reproduction 1: Factors Affecting Fertility and Fecundity
5.1 Introduction
5.1.1 The Role of Reproduction in the Productivity of Sheep Grazing Systems
5.1.2 The Major Factors Influencing Reproductive Rate
5.1.3 The Components of Reproductive Rate
5.1.4 Fertility, Fecundity and Survival Rate of Lambs to Marking Age
5.2 Physiological and Management Factors Affecting Fertility and Fecundity in the Ewe
5.2.1 Photoperiodicity in the Ewe
5.2.2 Effects of Body Weight and Nutrition on Ewe Fertility and Ovulation Rate
5.2.3 Flushing Ewes
5.2.4 Effect of Ewe Age on Fertility and Ovulation Rate
5.2.5 Ovulation without Oestrus
5.2.6 Failure of Fertilisation Due to Maternal Factors
5.2.7 Management of Ewes at Joining
5.3 Abnormalities and Diseases Affecting Ewe Fertility
5.3.1 Phyto-Oestrogenic Infertility
5.3.2 Embryo Mortality
5.4 Factors Affecting the Fertility of Rams Used for Natural Joining
5.4.1 Photoperiodicity in the Ram
5.4.2 Body Weight, Nutrition and Fertility in the Ram
5.4.3 Puberty and Age Effects in Rams
5.4.4 The Age Structure of the Ram Flock
5.4.5 Husbandry Procedures and Ram Fertility
5.4.6 Management of Rams at Joining
5.4.7 Failure of Fertilisation Due to an Inadequate Number of Rams
5.4.8 Failure of Fertilisation Due to Other Ram Factors
5.5 Abnormalities and Diseases Affecting Ram Fertility
5.5.1 Epididymitis Caused by Brucella ovis Infection (Ovine Brucellosis, OB)
5.5.2 Other Causes of Epididymitis
5.5.3 Non-Specific Abnormalities of the Epididymis
5.5.4 Testicular Abnormalities
5.5.5 Other Abnormalities Detected on Scrotal Palpation
5.5.6 Other Lesions of the Male Genitalia
Recommended Reading
General References
References
Chapter 6 Reproduction 2: Ultrasound Scanning for Pregnancy
6.1 The Application of Ultrasound Pregnancy Scanning on Sheep Farms
6.1.1 Reasons for Scanning
6.1.2 The Scanning Procedure
6.1.3 Scanning Windows
6.1.4 Counting Foetuses
6.1.5 Foetal Ageing
6.1.6 The Rate of Scanning
6.1.7 Pathological Diagnoses
6.2 The Reliability and Accuracy of Ultrasound Scanning for Pregnancy
6.2.1 Experienced Scanners and Good Conditions of Scanning
6.2.2 Understanding the Discrepancy between Scanning and Lambing Results
6.2.3 Measures of Accuracy
6.2.4 Studies of Scanning Accuracy
6.2.5 Accuracy of Scanning for Ageing Foetuses
6.2.6 Analysing Accuracy from Lambing Data
6.2.7 If the Number of Lambs Born Is Overestimated by Scanning (Direction of Error Is Lower)
6.2.8 If the Number of Lambs Born Is Underestimated at Scanning (Direction of Error Is Higher)
6.2.9 The Cost of Misclassification
6.3 Conclusion
References
Chapter 7 Reproduction 3: Disorders of Ewes in Pregnancy and Lactation, Abortion, Prenatal and Perinatal Diseases of Lambs
7.1 Husbandry of Ewes during Pregnancy
7.1.1 Length of Gestation
7.1.2 Nutrition during Pregnancy
7.1.3 Shearing and Crutching during Pregnancy and Lactation
7.2 Disorders of Ewes in Pregnancy
7.2.1 Pregnancy Toxaemia
7.2.2 Hypocalcaemia
7.2.3 Dorsal Vaginal Tear with Evisceration
7.2.4 Vaginal Prolapse
7.3 Abortion and Prenatal Diseases of Lambs
7.3.1 Introduction
7.3.2 Campylobacteriosis
7.3.3 Listeriosis
7.3.4 Toxoplasmosis
7.3.5 Chlamydial Abortion
7.3.6 Coxiellosis
7.3.7 Salmonellosis
7.3.8 Leptospirosis
7.3.9 Brucellosis
7.3.10 Ovine Pestivirus
7.3.11 Akabane Disease
7.3.12 Abortion Caused by Histophilus somni
7.3.13 Romulosis
7.4 The Lambing Process and Husbandry at Lambing
7.4.1 Parturition
7.4.2 Normal Ewe and Lamb Behaviour at Birth
7.4.3 The Influence of Lamb Birthweight on Survival
7.4.4 Husbandry at Lambing
7.5 Perinatal Lamb Mortality
7.5.1 Dystocia and Birth Injury
7.5.2 Starvation, Mismothering and Exposure
7.5.3 Minor Causes of Perinatal Mortalities
7.5.4 Post-Mortem Examination of Lambs
7.6 Disorders of the Ewe at Lambing
7.6.1 Dystocia
7.6.2 Uterine Prolapse
7.7 Nutrition during Lactation
7.8 Disorders of Lactating Ewes
7.8.1 Hypomagnesaemia
7.8.2 Undernutrition
7.8.3 Mastitis
7.8.4 Contagious Agalactia
7.9 Lamb Management at and after Marking
References
Chapter 8 Reproduction 4: Investigations of Poor Reproductive Rate in Commercial Sheep Flocks
8.1 Provision of Veterinary Advice about Reproductive Rate in Ewe Flocks
8.1.1 When Will Sheep Producers Seek Veterinary Advice?
8.1.2 What Constitutes a Poor Reproductive Rate?
8.2 Conducting an Investigation of Poor Reproductive Rates
8.2.1 A Conceptual Framework for Investigation
8.2.2 Collecting the History and Examining Records
8.2.3 Analysing and Interpreting Pregnancy Scanning Data
8.2.4 Examination of Ewes Soon after Scanning
8.2.5 Analysing and Interpreting Lamb Marking Data
8.2.6 Examination of the Ewes and Their Lambs Soon after Lamb Marking
8.2.7 Diagnostic Tools
References
Chapter 9 Reproduction 5: Controlled Breeding
9.1 Control of Oestrus and Ovulation
9.1.1 Synchronisation of Oestrus
9.1.2 Advancing the Breeding Season
9.1.3 Oestrus Stimulation in Ewes in Postpartum or Lactational Anoestrus
9.1.4 Increasing Fecundity
9.2 Induction of Abortion
9.3 Induction of Parturition
9.4 Artificial Insemination (AI)
9.4.1 Selection and Preparation of Rams
9.4.2 Collection of Semen
9.4.3 Handling of Semen
9.4.4 Evaluation of Semen
9.4.5 Dilution of Ram Semen
9.4.6 Storage of Ram Semen
9.4.7 Detection of Ewes in Oestrus
9.4.8 Insemination of the Ewe
9.5 Multiple Ovulation and Embryo Transfer (MOET)
9.5.1 Superovulation in Donor Ewes
9.5.2 Mating
9.5.3 Embryos
9.5.4 Transfers to Recipients
9.5.5 Expected Results for a MOET Programme
9.5.6 Schedule for the Preparation of Donor and Recipient Ewes
9.5.7 Storage of Embryos
9.6 Sperm Sexing
9.7 Juvenile in Vitro Embryo Technology (JIVET)
References
Chapter 10 Diseases Caused by Nematodes and Trematodes of Sheep
10.1 Introduction
10.2 Nematodiasis
10.2.1 Life Cycles
10.2.2 Survival of Free-Living Nematode Stages
10.2.3 Host Immunity and the Pathophysiology of Nematode Infections
10.2.4 Clinical Signs and Effects on Production
10.2.5 Diagnosis of Nematode Infections
10.3 Anthelmintics and Anthelmintic Resistance
10.3.1 Long-Acting Anthelmintics
10.3.2 Anthelmintic Resistance (AR)
10.3.3 Testing for Anthelmintic Resistance
10.3.4 Refugia
10.4 Epidemiology and Control of Nematode Infections
10.4.1 Patterns of Infection—Winter-Rainfall Areas
10.4.2 Control Programmes—Winter-Rainfall Areas
10.4.3 Patterns of Infection and Control Programmes—Summer-Rainfall Areas
10.4.4 Patterns of Infection and Control Programmes—Uniform-Rainfall Areas
10.4.5 Selection of Resistant Sheep
10.4.6 Nematode Control in Prime Lamb Systems
10.4.7 Biosecurity—Quarantine Drenching
10.5 Liver Fluke (Fasciola hepatica)
10.5.1 Life Cycle of Fasciola hepatica
10.5.2 Clinical Signs of Liver Fluke Infection
10.5.3 Epidemiology of Liver Fluke
10.5.4 Control Programmes for Liver Fluke
10.5.5 Flukicides and Resistance
10.5.6 Diagnosis of Liver Fluke
10.5.7 Testing for Flukicide Resistance
Further Reading and Resources
References
Chapter 11 Taeniid Cestodes and Sarcocystis of Sheep
11.1 Taeniid Cestodes
11.1.1 Introduction
11.1.2 Life Cycle
11.1.3 Zoonotic Potential
11.1.4 Control of Taeniid Cestodes on-Farm
11.1.5 Taenia ovis
11.1.6 Taenia hydatigena
11.1.7 Echinococcus granulosus
11.2 Sarcocystis spp
11.2.1 Cost to the Sheep Industry
11.2.2 Epidemiology
11.2.3 Control of Sarcocystis spp in Sheep
References
Chapter 12 Management and Diseases of Weaner Sheep
12.1 Weaner Ill-Thrift
12.1.1 Introduction
12.1.2 Predisposition to Weaner Ill-Thrift
12.1.3 Factors Contributing to the Liveweight of Weaners
12.1.4 The Association between Liveweight of Weaners and Mortality
12.1.5 The Association between Time of Lambing and Weaner Ill-Thrift
12.1.6 The Association between the Management of the Ewe Flock and Weaner Ill-Thrift
12.1.7 Introduction of Grain Feeding
12.1.8 Regular Provision of Supplementation to Weaners
12.1.9 Age at Weaning
12.1.10 Post-Weaning Management of Weaners
12.1.11 Preventive Medicine Programme for Merino Weaners
References
Chapter 13 Diseases Characterised by Lameness
13.1 Osteodystrophies
13.1.1 Osteoporosis
13.1.2 Osteomalacia and Rickets
13.1.3 Other Causes of Osteodystrophies
13.2 Viral Diseases Associated with Lameness
13.2.1 Contagious Pustular Dermatitis (CPD, Contagious Ecthyma, Scabby Mouth)
13.2.2 Foot and Mouth Disease (FMD)
13.2.3 Bluetongue
13.3 Bacterial Arthritis
13.3.1 Fibrinous Arthritis
13.3.2 Suppurative Arthritis
13.4 Bacterial Infections of the Limbs
13.4.1 Post-Dipping Lameness
13.4.2 Strawberry Footrot
13.5 Bacterial Infections of the Foot
13.5.1 Lamellar Suppuration (Toe Abscess or White Line Abscess)
13.5.2 Ovine Interdigital Dermatitis (OID)
13.5.3 Foot Abscess
13.5.4 Footrot
13.5.5 Contagious Ovine Digital Dermatitis (CODD)
Recommended Reading
References
Chapter 14 Diseases Characterised by Sudden Death
14.1 Introduction
14.2 Infectious Diseases Causing Sudden Death
14.2.1 Clostridial Disease of Ruminants
14.2.2 Enterotoxaemia (Pulpy Kidney)
14.2.3 Enterotoxaemia Caused by C. perfringens Types A, B, C and E
14.2.4 Infectious Necrotic Hepatitis (Black Disease)
14.2.5 Malignant Oedema and Swelled Head
14.2.6 Blackleg
14.2.7 Bacillary Haemoglobinuria
14.2.8 Braxy (Bradsot)
14.2.9 Clostridial Vaccines
14.2.10 Recommended Vaccination Programmes for Enterotoxaemia
14.2.11 Anthrax
14.2.12 Other Infectious Diseases Causing Sudden Death
14.3 Intoxications Causing Sudden Death
14.3.1 Poisoning with Inorganic Chemicals
14.3.2 Poisoning with Nitrate/Nitrite
14.3.3 Fluoroacetate Poisoning
14.3.4 Cardiac Glycoside Poisoning
14.3.5 Cyanogenic Glycosides
14.3.6 Green Cestrum Poisoning
14.3.7 Blue-Green Algal Poisoning
14.4 Environmental Conditions Causing Sudden Death
14.4.1 Lightning Strike
14.4.2 Exposure/Hypothermia
Recommended Reading
References
Chapter 15 Diseases of the Integument and Eye
15.1 Diseases of the Eye and Eyelids
15.1.1 Ovine Infectious Keratoconjunctivitis (Pink Eye)
15.1.2 Entropion
15.2 Bacterial and Viral Diseases of the Integument
15.2.1 Fleece Rot
15.2.2 Dermatophilosis (Dermo, Lumpy Wool)
15.2.3 Actinobacillosis
15.2.4 Contagious Pustular Dermatitis (Scabby Mouth, CPD)
15.2.5 Capripox Infection (Sheep and Goat Pox, SGP)
15.3 Non-Infectious Diseases of the Integument
15.3.1 Photosensitisation
15.3.2 Grass Seeds
15.3.3 Squamous Cell Carcinoma
15.3.4 Burns
15.3.5 Gangrene
15.3.6 Factors Affecting the Value of Sheep Skins
15.4 External Parasites
15.4.1 Flystrike (Cutaneous Myiasis)
15.4.2 Bovicola ovis
15.4.3 Psorobia ovis (Itchmite)
15.4.4 Chorioptes bovis
15.4.5 Other External Parasites of Sheep
15.4.6 Sheep Mites Exotic to Australia
Recommended Reading
References
Chapter 16 Diseases with Signs of Neurological Disturbance
16.1 Nutritional Deficiencies and Metabolic Disturbances
16.1.1 Polioencephalomalacia (PE)
16.1.2 Hypocalcaemia
16.1.3 Hypomagnesaemia
16.1.4 Kangaroo Gait
16.2 Infectious Diseases of the CNS
16.2.1 Focal Symmetrical Encephalomalacia (FSE)
16.2.2 Listeriosis
16.2.3 Brain and Spinal Cord Abscessation
16.2.4 Tetanus
16.2.5 Botulism
16.3 Infectious Conditions Leading to Congenital Neurological Disease
16.3.1 Border Disease (Hairy Shaker Disease)
16.3.2 Akabane and Aino Viruses
16.3.3 Schmallenberg Virus
16.3.4 Bluetongue
16.4 Non-Infectious Congenital and Inherited Conditions of the Nervous System
16.4.1 Enzootic Ataxia (Copper Deficiency)
16.4.2 Inherited and Possibly Inherited Disorders
16.5 Plant-Associated Toxicoses Causing Paresis, Paralysis and Gait Disturbances
16.5.1 Perennial Ryegrass Staggers, Perennial Ryegrass Toxicosis (PRGT)
16.5.2 Paspalum Staggers (Nervous Ergotism)
16.5.3 Annual Ryegrass Toxicity (ARGT)
16.5.4 Phalaris Staggers
16.5.5 Phalaris Sudden Death
16.5.6 Tribulus spp Staggers
16.5.7 Humpy Back
16.5.8 Swainsona spp Poisoning
16.5.9 Other Plant Intoxications with Signs of CNS Disturbance
16.6 Common Chemicals Responsible for Clinical Signs of Neurological Disease
16.6.1 Urea Toxicity
16.7 Clinical Differentiation of Neurological Conditions
16.7.1 Locomotor Disturbances
16.7.2 Dummy Syndromes and Recumbency
16.8 Exotic Diseases with Nervous Signs
16.8.1 Rabies
16.8.2 Scrapie
16.8.3 Ovine Encephalomyelitis (Louping Ill)
16.8.4 Coenurosis (Gid)
16.8.5 Aujeszky’s Disease (Pseudorabies)
16.8.6 Visna
16.8.7 Borna Disease
Recommended Reading
References
Chapter 17 Diseases of the Alimentary Tract
17.1 Gastrointestinal Diseases of Adult Sheep
17.1.1 Gastrointestinal Helminths
17.1.2 Ovine Johne’s Disease (OJD)
17.1.3 Intestinal Carcinoma
17.1.4 Phytobezoars and Trichobezoars
17.2 Gastrointestinal Diseases of Sheep of All Ages
17.2.1 Grain Poisoning (Grain Overload)
17.2.2 Red Gut (Haemorrhagic Enteritis)
17.2.3 Bloat
17.2.4 Enteric Salmonellosis
17.2.5 Diarrhoea of Unknown Cause in Adult Sheep (‘Winter Scours’)
17.2.6 Alimentary Tract Diseases Caused by Toxic Plants
17.3 Gastrointestinal Diseases of Young Sheep
17.3.1 Rotavirus
17.3.2 Coronavirus
17.3.3 Enterotoxigenic E. coli Infection
17.3.4 Cryptosporidium Infection
17.3.5 Coccidiosis
17.3.6 Yersiniosis
17.3.7 Campylobacteriosis
17.3.8 Differential Diagnosis of Scouring in Sheep
17.3.9 Abomasal Bloat of Lambs
17.4 Gastrointestinal Diseases Exotic to Australia
17.4.1 Bluetongue
17.4.2 Foot-and-Mouth Disease (FMD)
17.4.3 Rinderpest
17.4.4 Peste des Petits Ruminants (PPR)
Recommended Reading
References
Chapter 18 Diseases of the Liver
18.1 Liver Damage Caused by Mycotoxins
18.1.1 Phomopsin Intoxication (Lupinosis)
18.1.2 Prevention
18.1.3 Aflatoxin Intoxication
18.2 Pyrrolizidine Alkaloid Poisoning
18.2.1 Syndromes Caused by PA Ingestion
18.2.2 Chronic Copper Toxicity (Toxaemic Jaundice)
18.2.3 Chronic (Cumulative) Copper Poisoning following High Dietary or Parenteral Intake of Copper
18.2.4 Chronic (Cumulative) Copper Poisoning as a Consequence of Low Molybdenum Intake
18.2.5 Chronic (Cumulative) Copper Poisoning following Phytotoxic Liver Damage
18.2.6 Prevention
18.3 Other Diseases of the Liver
18.3.1 Liver Fluke (Fasciola hepatica)
18.3.2 Black Disease (Necrotic Hepatitis)
18.3.3 Hepatic Abscesses
18.3.4 Cobalt Deficiency (White Liver Disease)
18.3.5 Hepatic Lipidosis (Fatty Liver)
References
Chapter 19 Diseases of the Urinary System
19.1 Urolithiasis
19.1.1 The Development of Uroliths
19.1.2 Clinical Management of Urolithiasis
19.2 Posthitis, Balanitis, Vulvitis and Vulvovaginitis
19.2.1 Enzootic Posthitis
19.2.2 Ulcerative Balanitis and Vulvitis
19.3 Enlargement of Bulbo-Urethral Glands in Wethers
19.4 Diseases of the Kidney
19.4.1 Congenital Malformations
19.4.2 Immunologically Mediated Glomerulonephritis
19.4.3 Infectious Nephropathies
19.4.4 Tubular Necrosis Caused by Plant and Chemical Toxins
19.4.5 Oxalate Nephrosis
References
Chapter 20 Diseases of the Blood and Lymphatic System
20.1 Caseous Lymphadenitis (CLA)
20.1.1 Pathogenesis
20.1.2 Epidemiology
20.1.3 Effect on Productivity
20.1.4 Control Measures
20.1.5 Economics of Vaccination
20.1.6 Treatment
20.1.7 Diagnosis
20.2 Causes of Anaemia in Sheep
20.2.1 Infection with Mycoplasma ovis
20.2.2 Haemolytic Anaemia from SMCO-Containing Plants
20.2.3 Anaemia of Lambs from Bovine Colostrum
20.2.4 Bracken Fern Poisoning
Recommended Reading
References
Chapter 21 Diseases of the Respiratory System
21.1 Conditions of the Upper Respiratory Tract
21.1.1 Nasal Myiasis, Oestrus ovis Infestation
21.1.2 Infectious Conditions of the Nasal Cavity
21.1.3 Pharyngeal Trauma (Drenching Gun Injuries)
21.1.4 Laryngeal Chondritis
21.2 Conditions of the Lower Respiratory Tract
21.2.1 Introduction
21.2.2 Enzootic Pneumonia (Ovine Respiratory Complex)
21.2.3 Host and Environmental Factors Which Contribute to the Development of Ovine Pneumonia
21.2.4 The Spectrum of Respiratory Diseases and Nomenclature
21.2.5 Infectious Agents Causing Pneumonia in Sheep
21.2.6 Clinical Findings
21.2.7 Clinical Pathology
21.2.8 Necropsy Findings
21.2.9 Diagnosis
21.2.10 Treatment and Control
21.2.11 Prevention
21.3 Sporadic Conditions of the Lower Respiratory Tract
21.3.1 Parasitic Pneumonia
21.3.2 Aspiration Pneumonia
21.3.3 Lung Abscesses
21.3.4 Caseous Lymphadenitis (CLA)
21.3.5 Tuberculosis
21.3.6 Melioidosis
21.4 Diseases of the Lower Respiratory Tract Exotic to Australia
21.4.1 Ovine Pulmonary Adenocarcinoma (OPA, Jaagsiekte)
21.4.2 Maedi
References
Chapter 22 Anaesthesia and Analgesia for Sheep
22.1 Introduction
22.2 Anaesthesia
22.2.1 Preparation of the Sheep for Anaesthesia
22.2.2 Premedication
22.2.3 Induction of Anaesthesia
22.2.4 Maintenance of Anaesthesia
22.2.5 Supportive Care during Anaesthesia
22.2.6 Monitoring during Anaesthesia
22.2.7 Recovery from Anaesthesia
22.2.8 Common Complications during Anaesthesia
22.3 Local and Regional Anaesthesia
22.3.1 Common Local Anaesthetic Techniques
22.4 Analgesia
22.4.1 Pain Assessment
22.5 Peri-Operative Care
References
Index

Citation preview

Sheep Veterinary Practice “The value of this book cannot be overstated. As a student, many years ago, there were no comprehensive textbooks on sheep medicine, so I was lucky to have Professor Kym A Abbott as an inspiring lecturer. This book is needed by students!” Following on from Professor Abbott’s first book, The Practice of Sheep Veterinary Medicine, this new text remains the ideal reference for veterinarians in farm animal practice, veterinary and animal science students, agriculturalists and sheep producers. Principally addressing sheep health, welfare and production matters in Australia, this book also covers issues that are of relevance in many other countries of the world where sheep are raised. Sheep veterinary specialist Professor Kym Abbott and his co-authors inform the reader of the science underpinning the occurrence of disease syndromes, giving special attention to commonly investigated problems related to nutrition, reproduction and helminthiasis. Other disease conditions of sheep are discussed in subsequent chapters; first on the basis of presenting signs in the case of lameness and sudden death – conditions in which signs can be attributed to disorders of a variety of body systems – and then on a body-systems basis. This new edition thoroughly revises and expands on the previous text, adding a review of the systems and strategies available to improve the welfare of sheep in extensive farming systems, a chapter on pain relief, analgesia and anaesthesia for sheep, and a chapter on metacestodes. The text is illustrated with more than 150 full-colour images and photographs.

Sheep Veterinary Practice Edited by KYM A ABBOTT BVSc MVS PhD FANZCVS Adjunct Professor, Sheep Medicine The University of Adelaide

Designed cover image: Lesley Abbott First edition published 2024 by CRC Press 2385 NW Executive Center Drive, Suite 320, Boca Raton FL 33431 and by CRC Press 4 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN CRC Press is an imprint of Taylor & Francis Group, LLC © 2024 selection and editorial matter, Kym A Abbott; individual chapters, the contributors Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, access www.copyright.com or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978–750–8400. For works that are not available on CCC please contact mpkbookspermissions@ tandf.co.uk Trademark notice: Product or corporate names may be trademarks or registered trademarks and are used only for identification and explanation without intent to infringe. ISBN: 978-1-032-38288-3 (hbk) ISBN: 978-1-032-38283-8 (pbk) ISBN: 978-1-003-34434-6 (ebk) DOI: 10.1201/9781003344346 Typeset in Janson by Apex CoVantage, LLC

CONTENTS v

Preface About the Editor List of Contributors List of Abbreviations CHAPTER 1

xxv xxvii xxix xxxi

VETERINARY SERVICES TO SHEEP FARMS Kym A Abbott

1

1.1 The Role of the Veterinary Practitioner in the Australian Sheep Industry

1

1.1.1

The Levels of Sheep Veterinary Services

1

1.1.2

To Move from Generalist Practice to a Higher Level of Service

1

1.1.3

To Move from Level 2 Services to Level 3 Services

3

1.2 Important Industry Knowledge—The Elements of a Sheep Production System

3

1.2.1

Breed, Genotype and Genetic Merit

3

1.2.2

Production Objectives

6

1.2.3

Flock Structure

7

1.2.4

Stocking Rate

8

1.2.5

Farm Management Calendars

8

1.2.6

The Business Aspects of Sheep Farming

9

1.3 Investigations of Disease or Poor Performance in a Sheep Flock

11

1.3.1

Structure of the Investigation

11

1.4 Developing a Flock Health Programme

14

1.4.1

The Reasons for a Flock Health Programme

14

1.4.2

Delivery of the Programme

14

1.5 Body Condition Scoring and Its Relationship to Productivity

16

1.5.1

Usefulness of Body Condition Scoring

17

1.5.2

Reliability of the Technique

17

1.5.3

Relationship of Body Condition Score to Health and Productivity

17

1.5.4

Relationship of Body Condition Score to Welfare

17

1.5.5

The Use of Body Condition Score Targets

17

Recommended Reading

18

References

18

vi

CHAPTER 2

C on t e n t s

WELFARE OF SHEEP Andrew D Fisher and Natalie Roadknight

19

2.1 Concepts of Animal Welfare

19

2.1.1

What Is Animal Welfare?

19

2.1.2

Sentience

20

2.2 Sheep Behaviour and Sociability

20

2.2.1

Social and Predator Avoidance Behaviour

20

2.2.2

Abnormal Behaviours

21

2.2.3

Sheep Cognition

21

2.2.4

Learning

21

2.3 Sheep–Handler Interactions

21

2.3.1

Behavioural Handling Concepts

21

2.3.2

Handling Approaches and Yard Design

22

2.3.3

Sheep Neglect and Undernutrition

23

2.4 Husbandry Procedures and Alleviation of Pain

23

2.4.1

Tail Docking

23

2.4.2

Castration

24

2.4.3

Mulesing

25

2.4.4

Horn Trimming and Dehorning

27

2.4.5

Assisted Reproduction Procedures

27

2.5 Thermal Comfort

29

2.5.1

Heat Stress

29

2.5.2

Cold Stress

29

2.6 Welfare Impacts of Key Disease Conditions

30

2.6.1

Footrot

30

2.6.2

Mastitis

30

2.6.3

Lambing Losses

30

2.6.4

Flystrike

31

2.7 Humane Killing Techniques and Considerations

31

2.7.1

Anaesthetic Overdose

31

2.7.2

Gunshot

32

2.7.3

Captive Bolt Devices

32

2.7.4

Neonatal Lambs

32

2.7.5

Assessing Insensibility

32

2.7.6

Secondary Killing Methods

32

C on t e n t s

vii

2.7.7

Inhumane Methods

32

2.7.8

Confirming Death

32

2.7.9

Further Resources on Humane Killing

32

2.8 Assessment of Sheep following Bushfires

33

2.9 Welfare Monitoring and Record Keeping

34

2.10 Conclusions34 References34 CHAPTER 3

ENERGY AND PROTEIN NUTRITION OF GRAZING SHEEP Philip Hynd

39

3.1 Introduction39 3.2 Energy and Protein Requirements of Grazing Sheep

39

3.2.1

Ruminant Digestion

39

3.2.2

Estimating the Energy Requirements of Grazing Sheep

41

3.2.3

Maintenance Energy Requirement of Penned Sheep

42

3.2.4

Maintenance Energy Requirement of Actively Grazing Sheep

43

3.2.5

Maintenance Energy Requirements of Cold-Stressed Sheep

43

3.2.6

Metabolisable Energy Requirements for Gestation

44

3.2.7

Metabolisable Energy Requirements for Lactation

44

3.2.8

Guidelines for Managing Pregnant Ewes to Ensure High Rates of Lamb Survival and Lamb Growth to Weaning

45

3.2.9

Metabolisable Energy Requirements for Growing Weaners

46

3.2.10 Protein Requirements of Grazing Sheep

46

3.2.11 Nutrition and Wool Growth

48

3.3 Nutrition and Management of Grazing Sheep for Good Health and Production

50

3.3.1

Nutrient Supply from Pastures in Mediterranean and Cool Temperate Climates50

3.3.2

Matching Energy Demand with Energy Supply from Pastures

51

3.3.3

Relative Feeding Value of Legumes versus Grasses

51

3.3.4

Why Do Legumes Support Higher Levels of Animal Production than Grasses?51

3.3.5

Nutrient Supply from Pastures in Subtropical Climates

52

3.3.6

Feeding Behaviour of Grazing Animals

52

3.3.7

Grazing and Pasture Management for Sheep Production

53

3.3.8

Pasture Growth Rate and Phases of Plant Growth

53

3.3.9

Relationships between Herbage Mass, Nutritive Value of Pasture and Energy Intake in Sheep

54

3.3.10 Effect of Diet Selection on Pasture Growth

56

3.3.11 Grazing Management to Optimise Sheep Production per Hectare

56

viii

C on t e n t s

3.3.12 Stocking Rate, Stocking Density, Dry Sheep Equivalent and Sheep Production58 3.4 Estimating the Digestibility and Total Quantity of Feed on Offer in Grazed Pastures 3.4.1

Assessing Herbage Mass (Or Feed on Offer) in Pastures

3.5 Supplementation of Grazing Sheep

60 61 63

3.5.1

Cost of Supplements

64

3.5.2

Deciding the Level of Supplementation

64

3.6 Deleterious Compounds Found in Common Pasture Forages and Invasive Weeds of Pastures

69

3.7 Recommended Additional Resources

69

3.7.1

Decision Making in Grazing Sheep Enterprises

69

3.7.2

Drought Feeding Guide

70

References70 CHAPTER 4

CLINICAL ASPECTS OF TRACE ELEMENT AND VITAMIN NUTRITION Kym A Abbott

73

4.1 Copper (Cu)

73

4.1.1

Physiology73

4.1.2

Dietary Sources of Copper

73

4.1.3

Clinical Signs of Copper Deficiency

74

4.1.4

Subclinical Copper Deficiency

75

4.1.5

Seasonal Variations in Copper Availability

75

4.1.6

Clinical Pathology and Confirmation of Deficiency

75

4.1.7

Treatment and Prevention of Deficiency

77

4.2 Cobalt and Vitamin B1277 4.2.1

Physiology77

4.2.2

Dietary Sources of Cobalt

78

4.2.3

Pathophysiology of Cobalt Deficiency

78

4.2.4

Clinical and Subclinical Outcomes of Deficiency

79

4.2.5

Clinical Pathology and Confirmation of Deficiency

79

4.2.6

Treatment and Prevention of Deficiency

80

4.3 Selenium81 4.3.1

Introduction81

4.3.2

Physiology82

4.3.3

Dietary Requirements for Selenium

83

4.3.4

Seasonal Variation in Selenium Nutrition

84

C on t e n t s

ix

4.3.5

Signs of Selenium Deficiency

84

4.3.6

Subclinical Deficiency of Selenium

85

4.3.7

Clinical Pathology and Confirmation of Deficiency

85

4.3.8

Necropsy Findings

86

4.3.9

Treatment and Prevention of Deficiency

86

4.3.10 Selenium Toxicity 4.4 Vitamin E Deficiency

87 88

4.4.1

Introduction

88

4.4.2

Dietary Sources and Requirements of Vitamin E

89

4.4.3

Clinical and Necropsy Signs of Vitamin E Deficiency

89

4.4.4

Subclinical Deficiency of Vitamin E

90

4.4.5

Clinical Pathology and Confirmation of Deficiency

90

4.4.6

Treatment and Prevention of Deficiency

90

4.5 Differential Diagnosis of Myopathy

91

4.6 Iodine Deficiency (Including Goitre and Hypothyroidism)

92

4.6.1

Introduction

92

4.6.2

Goitrogens

93

4.6.3

Hypothyroidism Due to Inadequate Dietary Iodine

95

4.6.4

Inherited Hypothyroidism and Congenital Goitre

96

4.6.5

Hypothyroidism Due to the Ingestion of Goitrogens

96

4.6.6

Development of Hypothyroidism

97

4.6.7

Effects of Foetal Hypothyroidism

97

4.6.8

Clinical Signs of Iodine Deficiency

98

4.6.9

Diagnosis of Iodine Deficiency

99

4.6.10 Treatment and Prevention of Deficiency

99

4.7 Iron Nutrition

101

4.8 Molybdenum Nutrition

101

4.9 Manganese Nutrition

101

4.10 Zinc Nutrition

102

4.11 Investigation of Micronutrient Deficiencies

102

4.11.1 Clinical Pathology

102

4.11.2 Response Trials

104

4.12 Broad-Spectrum Supplementation

104

4.12.1 Licks and Blocks

104

4.12.2 Mineral Supplements for Oral Dosing and Risks of Mixing Products

104

Recommended Reading

105

References

105

x

CHAPTER 5

C on t e n t s

REPRODUCTION 1: FACTORS AFFECTING FERTILITY AND FECUNDITY Kym A Abbott

111

5.1 Introduction

111

5.1.1

The Role of Reproduction in the Productivity of Sheep Grazing Systems

111

5.1.2

The Major Factors Influencing Reproductive Rate

111

5.1.3

The Components of Reproductive Rate

112

5.1.4

Fertility, Fecundity and Survival Rate of Lambs to Marking Age

112

5.2 Physiological and Management Factors Affecting Fertility and Fecundity in the Ewe

113

5.2.1

Photoperiodicity in the Ewe

113

5.2.2

Effects of Body Weight and Nutrition on Ewe Fertility and Ovulation Rate

116

5.2.3

Flushing Ewes

117

5.2.4

Effect of Ewe Age on Fertility and Ovulation Rate

118

5.2.5

Ovulation without Oestrus

118

5.2.6

Failure of Fertilisation Due to Maternal Factors

118

5.2.7

Management of Ewes at Joining

118

5.3 Abnormalities and Diseases Affecting Ewe Fertility

119

5.3.1

Phyto-Oestrogenic Infertility

119

5.3.2

Embryo Mortality

120

5.4 Factors Affecting the Fertility of Rams Used for Natural Joining

122

5.4.1

Photoperiodicity in the Ram

122

5.4.2

Body Weight, Nutrition and Fertility in the Ram

123

5.4.3

Puberty and Age Effects in Rams

126

5.4.4

The Age Structure of the Ram Flock

127

5.4.5

Husbandry Procedures and Ram Fertility

127

5.4.6

Management of Rams at Joining

128

5.4.7

Failure of Fertilisation Due to an Inadequate Number of Rams

130

5.4.8

Failure of Fertilisation Due to Other Ram Factors

131

5.5 Abnormalities and Diseases Affecting Ram Fertility

131

5.5.1

Epididymitis Caused by Brucella ovis Infection (Ovine Brucellosis, OB)

131

5.5.2

Other Causes of Epididymitis

133

5.5.3

Non-Specific Abnormalities of the Epididymis

134

5.5.4

Testicular Abnormalities

134

5.5.5

Other Abnormalities Detected on Scrotal Palpation

135

5.5.6

Other Lesions of the Male Genitalia

136

C on t e n t s

xi

Recommended Reading

136

General References

136

References136 CHAPTER 6

REPRODUCTION 2: ULTRASOUND SCANNING FOR PREGNANCY Tristan Jubb

143

6.1 The Application of Ultrasound Pregnancy Scanning on Sheep Farms

143

6.1.1

Reasons for Scanning

143

6.1.2

The Scanning Procedure

144

6.1.3

Scanning Windows

145

6.1.4

Counting Foetuses

146

6.1.5

Foetal Ageing

146

6.1.6

The Rate of Scanning

146

6.1.7

Pathological Diagnoses

147

6.2 The Reliability and Accuracy of Ultrasound Scanning for Pregnancy

147

6.2.1

Experienced Scanners and Good Conditions of Scanning

147

6.2.2

Understanding the Discrepancy between Scanning and Lambing Results

148

6.2.3

Measures of Accuracy

149

6.2.4

Studies of Scanning Accuracy

150

6.2.5

Accuracy of Scanning for Ageing Foetuses

151

6.2.6

Analysing Accuracy from Lambing Data

152

6.2.7

If the Number of Lambs Born Is Overestimated by Scanning (Direction of Error Is Lower)

152

6.2.8

If the Number of Lambs Born Is Underestimated at Scanning (Direction of Error Is Higher)

154

6.2.9

The Cost of Misclassification

154

6.3 Conclusion155 References155 CHAPTER 7

REPRODUCTION 3: DISORDERS OF EWES IN PREGNANCY AND LACTATION, ABORTION, PRENATAL AND PERINATAL DISEASES OF LAMBS Caroline Jacobson, Tom Clune, Shane Besier, Stuart Barber and Kym A Abbott

157

7.1 Husbandry of Ewes during Pregnancy

157

7.1.1

Length of Gestation

157

7.1.2

Nutrition during Pregnancy

157

7.1.3

Shearing and Crutching during Pregnancy and Lactation

157

7.2 Disorders of Ewes in Pregnancy 7.2.1

Pregnancy Toxaemia

158 158

xii

C on t e n t s

7.2.2

Hypocalcaemia161

7.2.3

Dorsal Vaginal Tear with Evisceration

163

7.2.4

Vaginal Prolapse

163

7.3 Abortion and Prenatal Diseases of Lambs

164

7.3.1

Introduction164

7.3.2

Campylobacteriosis164

7.3.3

Listeriosis166

7.3.4

Toxoplasmosis167

7.3.5

Chlamydial Abortion

7.3.6

Coxiellosis168

7.3.7

Salmonellosis168

7.3.8

Leptospirosis169

7.3.9

Brucellosis169

167

7.3.10 Ovine Pestivirus

169

7.3.11 Akabane Disease

169

7.3.12 Abortion Caused by Histophilus somni170 7.3.13 Romulosis170 7.4 The Lambing Process and Husbandry at Lambing

170

7.4.1

Parturition170

7.4.2

Normal Ewe and Lamb Behaviour at Birth

170

7.4.3

The Influence of Lamb Birthweight on Survival

171

7.4.4

Husbandry at Lambing

172

7.5 Perinatal Lamb Mortality

173

7.5.1

Dystocia and Birth Injury

173

7.5.2

Starvation, Mismothering and Exposure

174

7.5.3

Minor Causes of Perinatal Mortalities

174

7.5.4

Post-Mortem Examination of Lambs

175

7.6 Disorders of the Ewe at Lambing

176

7.6.1

Dystocia176

7.6.2

Uterine Prolapse

176

7.7 Nutrition during Lactation

176

7.8 Disorders of Lactating Ewes

177

7.8.1

Hypomagnesaemia177

7.8.2

Undernutrition178

7.8.3

Mastitis178

7.8.4

Contagious Agalactia

7.9 Lamb Management at and after Marking

179 179

References180

C on t e n t s

CHAPTER 8

xiii

REPRODUCTION 4: INVESTIGATIONS OF POOR REPRODUCTIVE RATE IN COMMERCIAL SHEEP FLOCKS Tristan Jubb

187

8.1 Provision of Veterinary Advice about Reproductive Rate in Ewe Flocks

187

8.1.1

When Will Sheep Producers Seek Veterinary Advice?

187

8.1.2

What Constitutes a Poor Reproductive Rate?

187

8.2 Conducting an Investigation of Poor Reproductive Rates

189

8.2.1

A Conceptual Framework for Investigation

189

8.2.2

Collecting the History and Examining Records

190

8.2.3

Analysing and Interpreting Pregnancy Scanning Data

193

8.2.4

Examination of Ewes Soon after Scanning

194

8.2.5

Analysing and Interpreting Lamb Marking Data

195

8.2.6

Examination of the Ewes and Their Lambs Soon after Lamb Marking

196

8.2.7

Diagnostic Tools

197

References200 CHAPTER 9

REPRODUCTION 5: CONTROLLED BREEDING Simon de Graaf

201

9.1 Control of Oestrus and Ovulation

201

9.1.1

Synchronisation of Oestrus

201

9.1.2

Advancing the Breeding Season

202

9.1.3

Oestrus Stimulation in Ewes in Postpartum or Lactational Anoestrus205

9.1.4

Increasing Fecundity

205

9.2 Induction of Abortion

206

9.3 Induction of Parturition

206

9.4 Artificial Insemination (AI)

207

9.4.1

Selection and Preparation of Rams

207

9.4.2

Collection of Semen

207

9.4.3

Handling of Semen

208

9.4.4

Evaluation of Semen

208

9.4.5

Dilution of Ram Semen

209

9.4.6

Storage of Ram Semen

210

9.4.7

Detection of Ewes in Oestrus

210

9.4.8

Insemination of the Ewe

210

9.5 Multiple Ovulation and Embryo Transfer (MOET)

212

9.5.1

Superovulation in Donor Ewes

212

xiv

C on t e n t s

9.5.2

Mating212

9.5.3

Embryos213

9.5.4

Transfers to Recipients

213

9.5.5

Expected Results for a MOET Programme

213

9.5.6

Schedule for the Preparation of Donor and Recipient Ewes

214

9.5.7

Storage of Embryos

214

9.6 Sperm Sexing

214

9.7 Juvenile in Vitro Embryo Technology (JIVET)

215

References215 CHAPTER 10

DISEASES CAUSED BY NEMATODES AND TREMATODES OF SHEEP John Larsen

217

10.1 Introduction217 10.2 Nematodiasis217 10.2.1 Life Cycles

217

10.2.2 Survival of Free-Living Nematode Stages

221

10.2.3 Host Immunity and the Pathophysiology of Nematode Infections

221

10.2.4 Clinical Signs and Effects on Production

224

10.2.5 Diagnosis of Nematode Infections

226

10.3 Anthelmintics and Anthelmintic Resistance

228

10.3.1 Long-Acting Anthelmintics

229

10.3.2 Anthelmintic Resistance (AR)

229

10.3.3 Testing for Anthelmintic Resistance

230

10.3.4 Refugia230 10.4 Epidemiology and Control of Nematode Infections

231

10.4.1 Patterns of Infection—Winter-Rainfall Areas

232

10.4.2 Control Programmes—Winter-Rainfall Areas

233

10.4.3 Patterns of Infection and Control Programmes—SummerRainfall Areas

236

10.4.4 Patterns of Infection and Control Programmes—UniformRainfall Areas

238

10.4.5 Selection of Resistant Sheep

239

10.4.6 Nematode Control in Prime Lamb Systems

240

10.4.7 Biosecurity—Quarantine Drenching

241

10.5 Liver Fluke (Fasciola hepatica)241 10.5.1 Life Cycle of Fasciola hepatica241 10.5.2 Clinical Signs of Liver Fluke Infection

242

10.5.3 Epidemiology of Liver Fluke

242

10.5.4 Control Programmes for Liver Fluke

242

C on t e n t s

CHAPTER 11

10.5.5 Flukicides and Resistance

243

10.5.6 Diagnosis of Liver Fluke

245

10.5.7 Testing for Flukicide Resistance

246

Further Reading and Resources

246

References

251

TAENIID CESTODES AND SARCOCYSTIS OF SHEEP David Jenkins

261

11.1 Taeniid Cestodes

261

11.1.1 Introduction

261

11.1.2 Life Cycle

261

11.1.3 Zoonotic Potential

263

11.1.4 Control of Taeniid Cestodes on-Farm

263

11.1.5 Taenia ovis

263

11.1.6 Taenia hydatigena

266

11.1.7 Echinococcus granulosus

267

11.2 Sarcocystis spp

CHAPTER 12

xv

269

11.2.1 Cost to the Sheep Industry

269

11.2.2 Epidemiology

269

11.2.3 Control of Sarcocystis spp in Sheep

270

References

271

MANAGEMENT AND DISEASES OF WEANER SHEEP Kym A Abbott

273

12.1 Weaner Ill-Thrift

273

12.1.1 Introduction

273

12.1.2 Predisposition to Weaner Ill-Thrift

274

12.1.3 Factors Contributing to the Liveweight of Weaners

274

12.1.4 The Association between Liveweight of Weaners and Mortality

276

12.1.5 The Association between Time of Lambing and Weaner Ill-Thrift

276

12.1.6 The Association between the Management of the Ewe Flock and Weaner Ill-Thrift

276

12.1.7 Introduction of Grain Feeding

276

12.1.8 Regular Provision of Supplementation to Weaners

277

12.1.9 Age at Weaning

277

12.1.10 Post-Weaning Management of Weaners

277

12.1.11 Preventive Medicine Programme for Merino Weaners

279

References

280

xvi

CHAPTER 13

C on t e n t s

DISEASES CHARACTERISED BY LAMENESS Kym A Abbott

281

13.1 Osteodystrophies281 13.1.1 Osteoporosis281 13.1.2 Osteomalacia and Rickets

282

13.1.3 Other Causes of Osteodystrophies

286

13.2 Viral Diseases Associated with Lameness

286

13.2.1 Contagious Pustular Dermatitis (CPD, Contagious Ecthyma, Scabby Mouth)

286

13.2.2 Foot and Mouth Disease (FMD)

286

13.2.3 Bluetongue286 13.3 Bacterial Arthritis

286

13.3.1 Fibrinous Arthritis

287

13.3.2 Suppurative Arthritis

289

13.4 Bacterial Infections of the Limbs

289

13.4.1 Post-Dipping Lameness

289

13.4.2 Strawberry Footrot

290

13.5 Bacterial Infections of the Foot

290

13.5.1 Lamellar Suppuration (Toe Abscess or White Line Abscess)

290

13.5.2 Ovine Interdigital Dermatitis (OID)

291

13.5.3 Foot Abscess

292

13.5.4 Footrot293 13.5.5 Contagious Ovine Digital Dermatitis (CODD) Recommended Reading

310 310

References310 CHAPTER 14

DISEASES CHARACTERISED BY SUDDEN DEATH Kym A Abbott

319

14.1 Introduction319 14.2 Infectious Diseases Causing Sudden Death

319

14.2.1 Clostridial Disease of Ruminants

319

14.2.2 Enterotoxaemia (Pulpy Kidney)

319

14.2.3 Enterotoxaemia Caused by C. perfringens Types A, B, C and E

321

14.2.4 Infectious Necrotic Hepatitis (Black Disease)

321

14.2.5 Malignant Oedema and Swelled Head

321

14.2.6 Blackleg322 14.2.7 Bacillary Haemoglobinuria

322

C on t e n t s

xvii

14.2.8 Braxy (Bradsot)

322

14.2.9 Clostridial Vaccines

322

14.2.10 Recommended Vaccination Programmes for Enterotoxaemia

323

14.2.11 Anthrax324 14.2.12 Other Infectious Diseases Causing Sudden Death 14.3 Intoxications Causing Sudden Death

325 326

14.3.1 Poisoning with Inorganic Chemicals

326

14.3.2 Poisoning with Nitrate/Nitrite

327

14.3.3 Fluoroacetate Poisoning

328

14.3.4 Cardiac Glycoside Poisoning

329

14.3.5 Cyanogenic Glycosides

329

14.3.6 Green Cestrum Poisoning

330

14.3.7 Blue-Green Algal Poisoning

331

14.4 Environmental Conditions Causing Sudden Death 14.4.1 Lightning Strike

331 331

14.4.2 Exposure/Hypothermia331 Recommended Reading

332

References332 CHAPTER 15

DISEASES OF THE INTEGUMENT AND EYE Kym A Abbott

335

15.1 Diseases of the Eye and Eyelids

335

15.1.1 Ovine Infectious Keratoconjunctivitis (Pink Eye)

335

15.1.2 Entropion336 15.2 Bacterial and Viral Diseases of the Integument

337

15.2.1 Fleece Rot

337

15.2.2 Dermatophilosis (Dermo, Lumpy Wool)

338

15.2.3 Actinobacillosis338 15.2.4 Contagious Pustular Dermatitis (Scabby Mouth, CPD)

339

15.2.5 Capripox Infection (Sheep and Goat Pox, SGP)

340

15.3 Non-Infectious Diseases of the Integument

341

15.3.1 Photosensitisation341 15.3.2 Grass Seeds

345

15.3.3 Squamous Cell Carcinoma

346

15.3.4 Burns346 15.3.5 Gangrene346 15.3.6 Factors Affecting the Value of Sheep Skins

346

xviii

C on t e n t s

15.4 External Parasites 15.4.1 Flystrike (Cutaneous Myiasis)

347 347

15.4.2 Bovicola ovis349 15.4.3 Psorobia ovis (Itchmite)

354

15.4.4 Chorioptes bovis356 15.4.5 Other External Parasites of Sheep

356

15.4.6 Sheep Mites Exotic to Australia

356

Recommended Reading

357

References357 CHAPTER 16

DISEASES WITH SIGNS OF NEUROLOGICAL DISTURBANCE Kym A Abbott

363

16.1 Nutritional Deficiencies and Metabolic Disturbances

363

16.1.1 Polioencephalomalacia (PE)

363

16.1.2 Hypocalcaemia364 16.1.3 Hypomagnesaemia364 16.1.4 Kangaroo Gait 16.2 Infectious Diseases of the CNS 16.2.1 Focal Symmetrical Encephalomalacia (FSE)

364 365 365

16.2.2 Listeriosis365 16.2.3 Brain and Spinal Cord Abscessation

366

16.2.4 Tetanus367 16.2.5 Botulism368 16.3 Infectious Conditions Leading to Congenital Neurological Disease

368

16.3.1 Border Disease (Hairy Shaker Disease)

368

16.3.2 Akabane and Aino Viruses

369

16.3.3 Schmallenberg Virus

370

16.3.4 Bluetongue370 16.4 Non-Infectious Congenital and Inherited Conditions of the Nervous System

370

16.4.1 Enzootic Ataxia (Copper Deficiency)

370

16.4.2 Inherited and Possibly Inherited Disorders

370

16.5 Plant-Associated Toxicoses Causing Paresis, Paralysis and Gait Disturbances373 16.5.1 Perennial Ryegrass Staggers, Perennial Ryegrass Toxicosis (PRGT)373 16.5.2 Paspalum Staggers (Nervous Ergotism)

378

16.5.3 Annual Ryegrass Toxicity (ARGT)

378

16.5.4 Phalaris Staggers

380

C on t e n t s

xix

16.5.5 Phalaris Sudden Death

384

16.5.6 Tribulus spp Staggers

385

16.5.7 Humpy Back

385

16.5.8 Swainsona spp Poisoning

385

16.5.9 Other Plant Intoxications with Signs of CNS Disturbance

385

16.6 Common Chemicals Responsible for Clinical Signs of Neurological Disease 16.6.1 Urea Toxicity 16.7 Clinical Differentiation of Neurological Conditions

386 386 387

16.7.1 Locomotor Disturbances

387

16.7.2 Dummy Syndromes and Recumbency

388

16.8 Exotic Diseases with Nervous Signs

388

16.8.1 Rabies388 16.8.2 Scrapie389 16.8.3 Ovine Encephalomyelitis (Louping Ill)

391

16.8.4 Coenurosis (Gid)

391

16.8.5 Aujeszky’s Disease (Pseudorabies)

391

16.8.6 Visna392 16.8.7 Borna Disease Recommended Reading

392 392

References392 CHAPTER 17

DISEASES OF THE ALIMENTARY TRACT Kym A Abbott

399

17.1 Gastrointestinal Diseases of Adult Sheep

399

17.1.1 Gastrointestinal Helminths

399

17.1.2 Ovine Johne’s Disease (OJD)

399

17.1.3 Intestinal Carcinoma

411

17.1.4 Phytobezoars and Trichobezoars

411

17.2 Gastrointestinal Diseases of Sheep of All Ages

412

17.2.1 Grain Poisoning (Grain Overload)

412

17.2.2 Red Gut (Haemorrhagic Enteritis)

415

17.2.3 Bloat416 17.2.4 Enteric Salmonellosis

417

17.2.5 Diarrhoea of Unknown Cause in Adult Sheep (‘Winter Scours’)

417

17.2.6 Alimentary Tract Diseases Caused by Toxic Plants

418

17.3 Gastrointestinal Diseases of Young Sheep

418

17.3.1 Rotavirus418 17.3.2 Coronavirus419

xx

C on t e n t s

17.3.3 Enterotoxigenic E. coli Infection

419

17.3.4 Cryptosporidium Infection

420

17.3.5 Coccidiosis

422

17.3.6 Yersiniosis

424

17.3.7 Campylobacteriosis

425

17.3.8 Differential Diagnosis of Scouring in Sheep

425

17.3.9 Abomasal Bloat of Lambs

426

17.4 Gastrointestinal Diseases Exotic to Australia

CHAPTER 18

427

17.4.1 Bluetongue

427

17.4.2 Foot-and-Mouth Disease (FMD)

429

17.4.3 Rinderpest

430

17.4.4 Peste des Petits Ruminants (PPR)

431

Recommended Reading

431

References

431

DISEASES OF THE LIVER Kym A Abbott

441

18.1 Liver Damage Caused by Mycotoxins

441

18.1.1 Phomopsin Intoxication (Lupinosis)

441

18.1.2 Prevention

442

18.1.3 Aflatoxin Intoxication

443

18.2 Pyrrolizidine Alkaloid Poisoning

443

18.2.1 Syndromes Caused by PA Ingestion

443

18.2.2 Chronic Copper Toxicity (Toxaemic Jaundice)

445

18.2.3 Chronic (Cumulative) Copper Poisoning following High Dietary or Parenteral Intake of Copper

446

18.2.4 Chronic (Cumulative) Copper Poisoning as a Consequence of Low Molybdenum Intake

447

18.2.5 Chronic (Cumulative) Copper Poisoning following Phytotoxic Liver Damage

447

18.2.6 Prevention

449

18.3 Other Diseases of the Liver

449

18.3.1 Liver Fluke (Fasciola hepatica)

449

18.3.2 Black Disease (Necrotic Hepatitis)

449

18.3.3 Hepatic Abscesses

449

18.3.4 Cobalt Deficiency (White Liver Disease)

449

18.3.5 Hepatic Lipidosis (Fatty Liver)

449

References

449

C on t e n t s

CHAPTER 19

DISEASES OF THE URINARY SYSTEM Kym A Abbott

xxi

453

19.1 Urolithiasis453 19.1.1 The Development of Uroliths

453

19.1.2 Clinical Management of Urolithiasis

455

19.2 Posthitis, Balanitis, Vulvitis and Vulvovaginitis

457

19.2.1 Enzootic Posthitis

457

19.2.2 Ulcerative Balanitis and Vulvitis

460

19.3 Enlargement of Bulbo-Urethral Glands in Wethers

461

19.4 Diseases of the Kidney

462

19.4.1 Congenital Malformations

462

19.4.2 Immunologically Mediated Glomerulonephritis

462

19.4.3 Infectious Nephropathies

462

19.4.4 Tubular Necrosis Caused by Plant and Chemical Toxins

463

19.4.5 Oxalate Nephrosis

464

References468 CHAPTER 20

DISEASES OF THE BLOOD AND LYMPHATIC SYSTEM Kym A Abbott

473

20.1 Caseous Lymphadenitis (CLA)

473

20.1.1 Pathogenesis473 20.1.2 Epidemiology474 20.1.3 Effect on Productivity

476

20.1.4 Control Measures

476

20.1.5 Economics of Vaccination

477

20.1.6 Treatment477 20.1.7 Diagnosis477 20.2 Causes of Anaemia in Sheep

477

20.2.1 Infection with Mycoplasma ovis477 20.2.2 Haemolytic Anaemia from SMCO-Containing Plants

478

20.2.3 Anaemia of Lambs from Bovine Colostrum

478

20.2.4 Bracken Fern Poisoning

479

Recommended Reading

479

References479

xxii

CHAPTER 21

C on t e n t s

DISEASES OF THE RESPIRATORY SYSTEM Kym A Abbott

483

21.1 Conditions of the Upper Respiratory Tract

483

21.1.1 Nasal Myiasis, Oestrus ovis Infestation

483

21.1.2 Infectious Conditions of the Nasal Cavity

484

21.1.3 Pharyngeal Trauma (Drenching Gun Injuries)

484

21.1.4 Laryngeal Chondritis

485

21.2 Conditions of the Lower Respiratory Tract

487

21.2.1 Introduction487 21.2.2 Enzootic Pneumonia (Ovine Respiratory Complex)

487

21.2.3 Host and Environmental Factors Which Contribute to the Development of Ovine Pneumonia

488

21.2.4 The Spectrum of Respiratory Diseases and Nomenclature

490

21.2.5 Infectious Agents Causing Pneumonia in Sheep

491

21.2.6 Clinical Findings

497

21.2.7 Clinical Pathology

499

21.2.8 Necropsy Findings

499

21.2.9 Diagnosis500 21.2.10 Treatment and Control

500

21.2.11 Prevention501 21.3 Sporadic Conditions of the Lower Respiratory Tract

502

21.3.1 Parasitic Pneumonia

502

21.3.2 Aspiration Pneumonia

502

21.3.3 Lung Abscesses

503

21.3.4 Caseous Lymphadenitis (CLA)

503

21.3.5 Tuberculosis503 21.3.6 Melioidosis504 21.4 Diseases of the Lower Respiratory Tract Exotic to Australia 21.4.1 Ovine Pulmonary Adenocarcinoma (OPA, Jaagsiekte)

504 504

21.4.2 Maedi504 References505 CHAPTER 22

ANAESTHESIA AND ANALGESIA FOR SHEEP Gabrielle C Musk

509

22.1 Introduction509 22.2 Anaesthesia509 22.2.1 Preparation of the Sheep for Anaesthesia

509

C on t e n t s

xxiii

22.2.2 Premedication510 22.2.3 Induction of Anaesthesia

512

22.2.4 Maintenance of Anaesthesia

513

22.2.5 Supportive Care during Anaesthesia

514

22.2.6 Monitoring during Anaesthesia

515

22.2.7 Recovery from Anaesthesia

516

22.2.8 Common Complications during Anaesthesia

516

22.3 Local and Regional Anaesthesia 22.3.1 Common Local Anaesthetic Techniques

516 517

22.4 Analgesia518 22.4.1 Pain Assessment 22.5 Peri-Operative Care

519 519

References519 Index521

PREFACE xxv

Five years ago, with the assistance of four co-authors, I  published a book through my university’s publishing house which was the predecessor to this volume. That text had developed over many years, initially as a guide for senior veterinary students and then, on hearing that those early student versions were still being deployed in veterinary practices around Australia, as a more comprehensive reference book for students and graduates to support and encourage more veterinary involvement with sheep producers. That book appeared to be well received by practitioners and students, although there were several polite suggestions for ways in which the book could be more comprehensive in some areas, and generally more accessible. The lack of an index was a frustration for many—it seems that a searchable PDF is still not an adequate replacement. That issue and, hopefully, a few of the other deficiencies, have been addressed in this new book. The number of contributing authors has grown to thirteen and there have been substantial additions, particularly in the topics of animal welfare and anaesthesia and analgesia of sheep. The chapters on reproduction have been restructured and expanded, and five new authors with expertise in specific aspects of reproduction management have added valuable new material with insights based on their own fields of practice and research. The chapter on cestode and metacestode infections of sheep, formerly a small section in the first book, is now a stand-alone chapter written by an expert in the field. Other chapters have received varying degrees of expansion and updating. Reflecting the growing use of containment feeding of lambs in Australia and the growing recognition of the importance of respiratory disease in young sheep, the relevant chapter has been largely re-written. Sections on trace element nutrition, particularly iodine deficiency, and diseases of the neurological

system and urinary system have been substantially augmented. A  large number of small additions, particularly for less commonly encountered syndromes, has now been included across all chapters. In the original version of this text, there was a strong emphasis on providing information that was backed by scientific research and well-structured disease investigations. Wherever possible, peer-reviewed publications were used as the primary source of information, although non-peerreviewed reports of disease occurrences backed up with comprehensive laboratory investigations are also valuable and reliable. Consequently, there is, at the end of every chapter, a comprehensive list of references which should be consulted for readers who wish to read in greater depth about any of the statements or descriptions provided in the book. Hopefully, the references provided are the ones most likely to provide high-quality, reliable information relevant to the reader’s needs. Finally, my thanks to the contributing authors for their work, often under considerable pressure from their university teaching work in the difficult conditions which engulfed their institutions during and subsequent to the COVID-19 epidemic. My thanks also to my editor of the first text at University of Adelaide Press for her care, skill and hours of work—the results of her efforts remain in much of this current and expanded version—and to those who helped with their suggestions from using the previous text and encouraging the preparation of this volume. I also appreciate the suggestions from the several reviewers of draft chapters of this text. The need for a reference book for the general sheep veterinary practitioner, but with an Australian perspective, seems now well established and I hope this book gets closer to filling the gap. Kym A Abbott January 2024

ABOUT THE EDITOR xxvii

Dr  Kym A  Abbott worked in private practice as a farm animal practitioner then sheep veterinary consultant in South Australia and western Victoria before taking up academic appointments at The University of Sydney in 1992 and the Royal Veterinary

College, London, in 2001. He returned to Australia in 2004 to be Founding Head of the Veterinary School at Charles Sturt University, Wagga Wagga, New South Wales and then Head and Professor of Sheep Medicine at The University of Adelaide. Dr Kym A Abbott completed his MVS at the Mackinnon Project of The University of Melbourne in 1986 and PhD in ovine footrot at The University of Sydney in 2000.

CONTRIBUTORS xxix

Stuart Barber BVSc Ad Dip Ap Sc GCUT PhD Associate Professor, Animal Health, Welfare and Production Faculty of Veterinary and Agricultural Sciences The University of Melbourne

Caroline Jacobson BSc BVMS PhD Associate Professor, Biochemistry and Nutrition School of Agriculture, School of Veterinary Medicine Murdoch University

Shane Besier BSc BVMS MANZCVS DACVP Senior Veterinary Pathologist Diagnostic and Laboratory Service Department of Primary Industries and Regional Development, Western Australia

David Jenkins MSc PhD Associate Professor, Veterinary Parasitology School of Animal and Veterinary Sciences Charles Sturt University

Tom Clune BSc BVMS MANZCVS PhD Senior Lecturer, Production Animal Medicine School of Veterinary Medicine Murdoch University

Tristan Jubb BVSc MVS PhD Principal Bendigo Sheep Vets Strathdale, Victoria

Simon de Graaf FRSN FSRB Associate Professor, Animal Reproduction Animal Reproduction Unit The University of Sydney

John Larsen BVSc PhD Associate Professor and Honorary Research Fellow Mackinnon Project, Melbourne Veterinary School The University of Melbourne

Andrew D Fisher BVSc PhD FANZCVS Chair of Cattle and Sheep Production Medicine Faculty of Veterinary and Agricultural Sciences The University of Melbourne

Gabrielle C Musk BSc BVMS PhD Dipl ECVAA Veterinary Anaesthetist and Veterinary Officer Animal Care Services, Large Animal Facility University of Western Australia

Philip Hynd BSc PhD Emeritus Professor, Animal Production The University of Adelaide

Natalie Roadknight BA BVSc PhD FANZCVS Honorary Fellow The University of Melbourne

ABBREVIATIONS xxxi

ABARES Australian Bureau of Agricultural and Resource Economics ABLV Australian bat lyssavirus AGID Agar gel immunodiffusion AI Artificial insemination ALT Alanine amino transferase AMCP Amorphous magnesium calcium phosphate AMR Antimicrobial resistance ARGT Annual ryegrass toxicity AST Aspartate amino transferase ASBV Australian sheep breeding value ATP Adenosine triphosphate ATTM Ammonium tetrathiomolybdate AV Artificial vagina β-OH Beta-hydroxy BCS Body condition score BHB β-hydroxy butyrate BL-Mo Border Leicester × Merino BMR Basal metabolic rate BP Blood pressure BTV Bluetongue virus BUN Blood urea nitrogen BVD Bovine viral diarrhoea BW Body weight CarLA Carbohydrate larval antigen CASA Computer-assisted semen analyser CF Colonisation factor CFT Complement fixation test CIDR Controlled/constant internal drug release CJD Creutzfeldt–Jacob disease CK Creatine kinase CLA Caseous lymphadenitis CNP Chronic non-progressive pneumonia CO Cardiac output CO2 Carbon dioxide COWP Copper oxide wire particles CP Crude protein CPD Contagious pustular dermatitis CpHV1 Caprine herpes virus 1 CSIRO Commonwealth Scientific and Industrial Research Organisation CuSOD Copper superoxide dismutase

CVFD Coefficient of variation of fibre diameter DIT 3,5-diiodotyrosine DM Dry matter DMD Dry matter digestibility DMI Dry matter intake DNA Deoxyribonucleic acid DPLS Digestible protein leaving the stomachs DSE Dry sheep equivalent EAE Enzootic abortion of ewes EBLV European bat lyssavirus EBV Estimated breeding value eCG Equine chorionic gonadotrophin ELISA Enzyme-linked immunosorbent assay ENA Enzootic nasal adenocarcinoma ETEC Enterotoxigenic E. coli FD Fibre diameter FGA Flugestone acetate FHP Fasting heat production FMD Foot and mouth disease FME Fermentable metabolisable energy FOO Food on offer FSE Focal symmetrical encephalomalacia FSH Follicle-stimulating hormone GFW Greasy fleece weight GnRH Gonadotropin releasing hormone GPx Glutathione peroxidase HR Heart rate HT Hydrolysable tannins IDD Iodine deficiency disorder IFAA Indirect immunofluorescent antibody assay IgA Immunoglobulin A IgG Immunoglobulin G IPM Integrated parasite management IRP Iron-regulated proteins IS Insertion sequence IV Intravenous IVF In vitro fertilisation IVM In vitro maturation IVP Produced in vitro IVRA Intravenous regional anaesthesia JIVET Juvenile in vitro embryo technology JSRV Jaagsietke sheep retrovirus

xxxii

A bbr e v i at ions

L Lumbar vertebra (1 to 7) LCT Lower critical temperature LAM Lupinosis-associated myopathy LB/EJ Lambs born per ewe joined LH Luteinising hormone LKT Leukotoxin LM/EJ Lambs marked per ewe joined LT Heat-labile enterotoxin LW Liveweight MAC Minimum alveolar concentration MAP Mycobacterium avium subsp paratuberculosis MAP Market assurance program MCGN Mesangiocapillary glomerulonephritis MCPA 2-methyl-4-chlorophenoxyacetic acid MD Metabolisable energy density (MJ ME/kg DM) ME Metabolisable energy MIT 3-monoiodotyrosine MIVET Mature in vitro embryo transfer MMA Methylmalonic acid MOET Multiple ovulation and embryo transfer NE Net energy NMDA N-methyl-D-aspartate NSAID Non-steroidal anti-inflammatory drug NSW New South Wales NZ New Zealand OB Ovine brucellosis OJD Ovine Johne’s disease OvHV2 Ovine herpesvirus 2 OMP Outer membrane proteins OP Organophosphate OPA Ovine pulmonary adenocarcinoma OPU Oocyte pick up OR Ovulation rate OZT Oxazolidine-2-thiones PA Pyrrolizidine alkaloid PAPP Para-aminopropiophenone PCR Polymerase chain reaction PCR-REA Polymerase chain reaction and restriction endonuclease analysis PE Polioencephalomalacia PHGPx Phospholipid hydroperoxide glutathione peroxidase PFGE Pulsed-field gel electrophoresis PG Prostaglandin PI3 Parainfluenza virus type 3 PMSG Pregnant mare serum gonadotrophin PPR Peste des petits ruminants

PRG PRGT PTH PUFA RABV RDP RFLP SA SAMM SMCO SNP SP SRU ST ST SV T T3 T4 TPR TSE TSH UDP UHT UK UV VFA WA WEC WMD WNM ZN

Perennial ryegrass Perennial ryegrass toxicity Parathyroid hormone Polyunsaturated fatty acid Classical rabies virus Rumen-degradable protein Restriction fragment length polymorphism South Australia South African Mutton Merino S-methylcysteine sulfoxide Single nucleotide polymorphism Synthetic pyrethroid Selenium-responsive unthriftiness Heat-stable enterotoxin Sequence type Stroke volume Thoracic vertebra (1 to 13) Triiodothyronine Thyroxine Total peripheral resistance Transmissible spongiform encephalopathy Thyroid-stimulating hormone Undegraded dietary protein Ultra-high temperature United Kingdom Ultraviolet Volatile fatty acids Western Australia Worm egg count White muscle disease Weaner nutritional myopathy Ziehl–Neelson

UNITS OF MEASUREMENT kg g ha L m mL MJ mol nmol pmol ppm µm µmol

Kilogram Gram Hectare Litre Metre Millilitre Megajoule Mole Nanomole (10 −9 moles) Picomole (10 −12 moles) Parts per million Micrometre or micron Micromole (10 −6 moles)

chapter 1

VETERINARY SERVICES TO SHEEP FARMS 1

Kym A Abbott

1.1  THE ROLE OF THE VETERINARY PRACTITIONER IN THE AUSTRALIAN SHEEP INDUSTRY The Australian sheep industry has been well-served by the veterinary profession over the past century. The work of research scientists in government institutions, CSIROa and universities has led to many innovations, technologies and products which have dramatically improved the health of sheep and the productivity of sheep farms. Veterinary field officers from state departments of agriculture and, in New South Wales, the rate-payer funded Local Land Services organisation, provide extension and disease investigation services and have done so for many years. Private veterinary practitioners have generally been less involved in sheep veterinary services, although there are some notable exceptions. There remains substantial opportunity for a greater involvement of the private sector in sheep veterinary services. The gradual reduction in government-sponsored work and the growing interest of consumers in the welfare history of sheep products are continuing to expand the potential roles of the private vet in sheep production.

1.1.1  The Levels of Sheep Veterinary Services Existing veterinary services from private practitioners to sheep producers in Australia fall broadly into three categories. First, there are veterinarians in generalist rural practices who provide competent diagnostic services in the event of disease outbreaks on sheep farms and supply appropriate prescription-only drugs to their clients when required. They provide an important service which is appreciated by their sheep-owning clients but often have competing professional interests which limit the time they have for developing more complex sheep medicine activities or services. At the second level, there are veterinarians in rural practices who have a strong interest in sheep medicine and have spent professional development time learning more  CSIRO. Commonwealth Scientific and Industrial Research Organisation.

a

about the management of sheep health and the operation of sheep farms. These veterinarians are capable of working in sheep medicine at a more involved and broader level (I will call it Level 2 services) than their generalist colleagues. A third group includes the few veterinary practitioners in Australia who work predominantly or exclusively with sheep. These veterinarians are effectively specialists, although not usually registered as such. Some provide services aimed primarily at sheep health, welfare and productivity—Level 3 services for the purposes of the discussion here—and some provide artificial breeding services for semen collection and storage, artificial insemination and embryo transfer.

1.1.2  To Move from Generalist Practice to a Higher Level of Service There are multiple reasons for the relatively low involvement of veterinary practitioners with sheep farms in Australia. One reason is the relatively low expectations of sheep farmers for veterinary services, based on experience over many years and, often, an attitude passed on between generations of sheep-raising families. Another reason is the lack of confidence experienced by many new veterinary graduates—particularly those without a background in sheep farming—when offering advice to sheep producers. Their veterinary acumen is not in doubt, but their familiarity with sheep-farming activities is often very limited. A sheep farm can feel like a foreign place to a recent graduate raised in an urban environment. The problem is not unique to Australia. In the United Kingdom (UK), surveys have found that many veterinarians in rural practice believe that they could, or should, engage more with their sheep-owning clients but lack sufficient knowledge of sheep husbandry, the non-veterinary aspects of sheep farming and the needs of their clients.1 The sheep producers themselves have similar views.2 The consequence is an impasse—the veterinarian is not motivated to actively offer on-farm services beyond those requested by the producer, while the producers themselves are reluctant to request more than basic veterinary services because they suspect they will not receive good value. Some of the steps required for the inexperienced, budding sheep veterinarian to move to a higher level of service

DOI: 10.1201/9781003344346-1

2

CHAPTER 1: Veterinary Services to Sheep Farms

are described herein, but the most basic piece of advice is for the veterinarian to take every opportunity to visit sheep farms and to pursue disease investigations on the property rather than providing only telephone advice or offering services or advice only at the veterinary clinic. The familiarity of sheep-farming systems and the understanding of client needs will ultimately only develop through experience of working on-farm and listening to sheep-farming clients in their own workplace.

1.1.2.1  Developing Strong Industry Knowledge When investigating an occurrence of disease in one or more animals, history collection is usually the first step. To ask appropriate questions, both for the sake of gathering relevant information and for inspiring confidence in the client, the veterinarian’s questions need to be ‘informed’. The veterinarian needs to know enough about sheep husbandry to ask good questions. This requires a knowledge of the essential elements of a sheep production system—described a little more in the following section of this chapter, but includes: • Being able to recognise the breeds of sheep and know their characteristics • Appreciating the differences between different sheep production systems • Knowing about flock structures and the likely composition of a client’s sheep flock • Appreciating the structure of a farm calendar and the timing of the common husbandry events on a client’s sheep farm • Awareness of the business aspects of sheep farming

1.1.2.2  Developing Good Physical Skills For the veterinarian to be confident in his or her approach to a disease investigation, and for the client to be confident in the veterinarian, it is important that the veterinarian is able to handle sheep and perform common sheep veterinary procedures with obvious competence. The minimum set of physical skills includes: • • • • •

Sheep handling, restraining and tipping Body condition scoring Blood collection Necropsy Vasectomy

1.1.2.3  Developing Post-Graduate Sheep Medicine Knowledge Continuing professional development is now a requirement for registration for Australian veterinarians. Some

choose to do this through preparation for the membership qualification of the Australian and New Zealand College of Veterinary Scientists. While such a qualification is not essential to the pursuit of further education, the standards for membership do provide a guide to the knowledge that is appropriate for a special veterinary interest in sheep. The skills of particular importance include: • A broad knowledge of sheep diseases and their control • The ability to use a population medicine approach to disease control • The ability to conduct a disease investigation on a sheep farm • A working familiarity with relevant extension programmes and on-line resources developed for producers and advisors by industry bodies • A well-developed knowledge in fields which are most likely to initiate veterinary intervention: • Reproduction • Nutrition • Parasitology • Biosecurity, specifically lice, footrot, Johne’s disease, anthelmintic-resistant parasites Developing these skills and improving one’s knowledge is not straightforward in a busy practice. A few steps that some veterinarians have found helpful include: • Spending time with one or more veterinarians or sheep advisors with high-level expertise • Participating in conferences and webinars • Joining a study programme • Identifying a client to use as a ‘special project’ and learning from that client • Using every opportunity possible to get on-farm and learning ‘on the job’ Subsequent chapters are intended to help veterinarians to develop a sound level of knowledge and expertise, but a few preliminary comments about the practicalities of working with sheep producers and ways to get started in sheep veterinary practice may provide a helpful context for what follows later in the book.

1.1.2.4  Offering Services to Sheep-Farming Clients 1.1.2.4.1  Responding to Client Requests for Service Many sheep producers respond enthusiastically to a veterinarian who demonstrates a keen interest in, and aptitude for, sheep veterinary work. Often the starting point for a vet–client relationship is an investigation of one or more unexpected deaths or an outbreak of signs of serious

1. 2 I m p or ta n t I n dus t ry K now l e d g e —Th e E l e m e n t s of a Sh e e p P roduc t ion Sys t e m

disease like scouring, lameness or wasting. While it may be possible to satisfy the client’s expectations by conducting necropsies at the clinic or examining a few sheep brought to the clinic, such an approach could easily miss some very important information. A visit to the farm provides a much better opportunity for the veterinarian to (1) choose the most appropriate animals to examine, dead or alive; (2) appreciate the environment on the farm which has led to, or influenced, the disease occurrence; and (3) collect further specimens to help the investigation, if necessary. An enthusiastic, thorough investigation and expedient communication back to the client of any results from laboratory tests will inspire the client’s confidence in the veterinarian and encourage an ongoing professional relationship. 1.1.2.4.2  Offering a Preventive Medicine Service—A Flock Health Programme Many sheep producers will benefit substantially from a preventive medicine programme or flock health programme which is aimed at improving the health, welfare and productivity of the client’s flock via better monitoring of sheep health and better plans for prevention and control of disease. In some cases, clients may request such a service, but, in Australia at least, most sheep producers are not aware of such a service and are likely to be initially doubtful of its value when they do hear of it. The offer of a flock health programme—even if the offer is limited only to some components of a programme, pre-joining ram soundness examinations for example— should be made when (1) the veterinarian clearly identifies the need for preventive medicine strategies on a farm, (2) when the veterinarian believes he or she possesses the necessary skills and knowledge to deliver the service competently and (3) when the client has confidence that the veterinarian’s advice is well founded and sound. A suggested structure of a flock health programme is provided later in this chapter.

1.1.3  To Move from Level 2 Services to Level 3 Services The step from the provision of high-quality sheep medicine services from a general practice to a sheep-only practice requires all of the previously listed skills plus some additional training, coupled with substantial experience. A critical attribute for this level is a knowledge of the business basis for sheep farm activities and the practical challenges of operating a sheep farm. The role of the specialist sheep-only veterinary practitioner moves closer to that of a consultant, in which the veterinarian is likely to take a more analytical approach to farm activities and production

3

and be the person who identifies the problem area rather than only responding to concerns raised by the client. At this level of veterinary service there is less of the ‘fire-brigade’ type of work and more time spent on the delivery of the flock health programme, and the advice given within the flock health programme is much more likely to also include production-limiting issues involving husbandry and management strategies. Farm decisions around time of lambing, time of shearing, stocking rate, breed, genotype and ram selection are more likely to be discussed, as these decisions have strong interactions with sheep numbers, reproduction, nutrition, health and meat and wool productivity. Veterinarians working at this level are also likely to be involved in on-farm research, consultancies to industry bodies and the provision of training to producers and other veterinarians.

1.2  IMPORTANT INDUSTRY KNOWLEDGE—THE ELEMENTS OF A SHEEP PRODUCTION SYSTEM The essential elements of a sheep production system include: (1) the breed and genotype of sheep in the flock, (2) the production objectives of the flock, (3) the flock size and composition and (4) the farm’s management calendar.

1.2.1  Breed, Genotypeb and Genetic Merit 1.2.1.1  Breeds of Sheep Used in Australia 1.2.1.1.1 Merino Purebred Merinos dominate the national sheep flock, making up approximately 75% of the sheep shorn in 2020.3 Merinos are considered a wool-producing breed with limited suitability as a meat sheep, but the larger-framed medium- and strong-wool Merinos are increasingly being selected for characteristics which enhance both meat and wool production. The Dohne Merino and South African Mutton Merino (SAMM) were introduced into Australia in 1988 and 1996, respectively, and are present in much smaller numbers. 1.2.1.1.2  Maternal Breeds Maternal breeds are those which are chosen for their relatively high fecundity (compared to the Merino) and mothering ability in addition to traits directly relevant to sheep-meat production. The most commonly used maternal breed in Australia is the Border Leicester. Other breeds b The word genotype usually describes a subpopulation of a breed, the individuals of which share distinctive genetic characteristics; it may therefore be used to denote a strain or a bloodline of a breed.

4

CHAPTER 1: Veterinary Services to Sheep Farms

include the Romney, Coopworth, Cheviot and Lincoln. These breeds are often grouped together as the British longwool breeds. The Finn (originally Finnish Landrace) is a highly prolific maternal breed of Scandinavian origin. In Australia rams of maternal breeds (predominantly Border Leicester) are usually crossed with Merino to produce a ‘first-cross’ ewe to mate to terminal breed sires. 1.2.1.1.3  First-Cross Ewes Approximately 10% of the national flock are Border Leicester × Merino ewes (BL-Mo)—often just called first-cross ewes—and these are the most common type used as dams in flocks breeding second-cross lambs for meat. Second-cross lambs are those sired by a ram of a meat breed, and their high growth rate, excellent muscling and relative leanness make them highly suitable for meat production. 1.2.1.1.4  Shedding Breeds Shedding or clean-skin breeds of sheep shed their fleeces naturally every year, so shearing is not required, and no income, therefore, is derived from wool. Breeds of this type in Australia include the Dorper, White Dorper, Damara, Wiltshire Horn, Wiltipolls and breeds derived from a range of crosses. Hair breeds of sheep now introduced into Australia include the Namaqua, Van Rooy and Afrikaner, all of which shed their fleeces annually. 1.2.1.1.5 Composites Around 8% of the Australian national sheep flock are sheep of the ‘composite’ breeds, most of which shed their fleeces annually and do not require shearing. These are meatsheep breeds developed from other traditional breeds. An example is the Australian White, developed from the Van Rooy, White Dorper, Poll Dorset and Texel breeds. There are numerous others. 1.2.1.1.6  Terminal Sire Breeds The breeds which are used as prime lamb sires include Poll Dorset, White Suffolk, Texel, Suffolk and composites. Sheep of these breeds are selected for their meat-production qualities, and wool is of no economic importance. 1.2.1.1.7  Dual-Purpose Breeds In addition to some larger types of Merinos which have ‘dual-purpose’ characteristics, there are some breeds considered dual-purpose (meat and wool), and the Corriedale is the most populous of these in Australia. Others include the Polwarth, the Romney and the Coopworth, although the latter two breeds produce wool of very high fibre diameter compared to the Merino, Polwarth and Corriedale.

The Polwarth and Corriedale are both derived from British longwool breeds and the Merino. Crosses between the Merino and Corriedale, Polwarth or first-cross sheep are referred to as ‘comebacks’. 1.2.1.1.8  Dairy Breeds The Awassi and East Friesian breeds were introduced to Australia in the 1990s. Most milking sheep in Australia are crosses between these breeds and more common breeds such as the Poll Dorset and Border Leicester. 1.2.1.1.9  Other Breeds The list of breeds briefly described earlier is not exhaustive, and there are other breeds present in Australia in relatively low numbers. A  detailed discussion about the characteristics of each breed and the factors which make some breeds and genotypes more or less suitable for particular environments is beyond the scope of this text, and veterinarians working with sheep are encouraged to seek more information from other reliable sources.

1.2.1.2  Genotypes and Genetic Differences Within Breeds 1.2.1.2.1  The Types, Strains and Bloodlines of the Australian Merino Australian breeders of Merino sheep recognise distinct strains of the breed, reflecting their separate development in different parts of Australia commencing in the late nineteenth century. Some characteristics which distinguish the strains are presented in Table 1.1 as a guide.4 Within the Merino breed some breeders produce Poll Merinos rather than (horned) Merinos, and some produce both Merinos (horned) and Poll Merinos. Within the strains of Merino there are bloodlines, a term which refers to the parent stud responsible for the genetic characteristics of the type. Parent studs are those which have been closed to the introduction of new rams for an extended period. Daughter studs are associated with each parent stud and perform the role of multiplication by purchasing rams of high merit from parent studs and producing multiple sons from each ram, most of which are then sold to commercial flock owners as flock rams. Many sheep breeders continue to maintain their flocks ‘true to type’ and remain with a traditional bloodline, but there is a growing movement towards the use of crossflock genetic comparisons to inform breeding decisions by both ram breeders and commercial breeders. Increasingly, progressive studs and ram breeders are becoming concerned less about bloodlines and more about objective measures of genetic merit, as produced by the Sheep Genetics database.

1. 2 I m p or ta n t I n dus t ry K now l e d g e —Th e E l e m e n t s of a Sh e e p P roduc t ion Sys t e m

5

Table 1.1  Some of the Characteristics which Differentiate the Main Strains of the Australian Merino Breed MEDIUM PEPPIN

MEDIUM NON-PEPPIN

FINE-WOOL OR SAXON

SOUTH AUSTRALIAN

GENERAL DESCRIPTION

MEDIUM WOOL

MEDIUM WOOL

FINE WOOL

STRONG WOOL

Average fibre diameter of fleece

18–22 µm

17–21 µm

< 18 µm

22–24 µm

Typical fleeceweights (clean)

3.2 kg

3.0 kg

2.5 kg

3.7 kg

Adult liveweights

45–50 kg

42–47 kg

40–45 kg

50–55 kg

Propensity for skin wrinkle

++

++

+++

+

Seasonality of reproduction (compared within the breed)

++

++

+++

+

Lambs born per 100 ewes

90–95

90–95

85–90

95–100

Note: These characteristics are strongly influenced by the environment in which sheep are raised, so the data are presented for comparative purposes only. Except for fibre diameter, the differences between strains are based on data from Dolling (1970).4

1.2.1.2.2  Sheep Genetics Database There are significant differences in the productivity of Merino sheep between different bloodlines (genotypes) and large differences between individual rams within a flock. Information about these differences is becoming increasingly available to Australian sheep producers through the national genetic evaluation programmes in Sheep Genetics. Sheep Genetics is a service for the Australian sheep and goat industries operated by Meat and Livestock Australia.c There are three separate databases for sheep— LAMBPLAN for prime lamb sires, MERINOSELECT for Merino sires and DOHNE ASBVs for Dohne Merino rams. The databases provide Australian sheep breeding values (ASBVs—the equivalent of estimated breeding values or EBVs) for rams produced by contributing breeders. ASBVs for all rams are provided on one scale, so all rams in all years of birth can be compared. A commercial producer is able to use the information provided on the Sheep Genetics website (often reproduced in the ram breeder’s sale catalogue) to identify rams with ASBVs of high merit in the traits of interest. For Merino producers, those traits may be related to annual fleece production, average fibre diameter or other wool quality traits, as well as conformational traits, including those related to skin wrinkle or meat production.

evaluating their progeny. The sites and years are linked by link-sires, so the results from all rams in all trials in all years are directly comparable. Results are published annually and are available on the Association’s website.d For each sire, a wide range of traits are reported as ASBVs and traits of economic importance are combined into indices. Each index has different weights (economic values) attached to the traits of interest. For example, the dual-purpose index applies high weights to clean fleece wool production, weaning rate and bodyweight, while the fibre production index applies most weight to fibre fineness, fleece weight and staple strength. There is also a Merino production index and a wool production index. Because the ASBVs and index values are produced by progeny testing with the progeny at each site managed together, the accuracies attached to the ASBVs are high or, in the case of rams with many progeny, very high. Semen is available for sale from some rams listed in the Merino superior sires publication. In Australia most artificial insemination (AI) programmes in sheep are conducted in ram-breeding flocks and not commercial flocks. Some commercial producers, however, run their own AI programmes, producing rams to use in their own commercial flocks.5 The production of ewe progeny of high merit from the AI programme is then a bonus on top of the production of rams.

1.2.1.2.3  Merino Superior Sires The Australian Merino Sires Evaluation Association, supported by Australian Wool Innovation (AWI), operates trials across different sites in Australia comparing the breeding performance of Merino sires by comparing and

1.2.1.2.4  How Does a Commercial Sheep Breeder Use the Information in the Databases? Most commercial sheep breeders buy rams from studs or non-stud ram breeders. In most cases they buy from one source only and usually continue to buy from that source

 https://www.sheepgenetics.org.au/

c

 https://merinosuperiorsires.com.au/

d

6

CHAPTER 1: VETERinARy SERViCES To SHEEP FARmS

each year. For those producers, their choice of rams to purchase is constrained to those available from one rambreeding flock. They can use the ASBVs (which should be available in the sale catalogue) to inform their buying decisions but, clearly, can only choose from what is available from that supplier. A ram buyer can also consider buying rams from a different source, and the availability and comparability of ASBVs allows buyers to make comparisons between sources. For example, a Merino sheep producer may consider that fibre fineness is important but under-rated in importance by the operator of his or her current ram source. It is possible, although not always straightforward logistically, to look at the range of rams and ASBVs related to fibre diameter that are available at another ram source. Creating a table like Table 1.2 might assist. There is no point looking for a very fine-wooled ram in a strong-wool stud, or a sire of large progeny in a fine-wool stud. There are unlikely to be many, or any, available for sale at realistic prices. Similarly, a ram buyer can look at the information on Merino Superior Sires and identify rams of interest in that database and then identify the ram breeders who produced the sires, or the ram breeders who are using the sire, and investigate the ASBVs of their sale rams. Ram breeders who produce or use rams with high index values may be a good place to start when exploring options to identify the best source of rams to meet the needs of the commercial producer.

Table 1.2 The Average ASBVs of Flock Rams from the Sales Catalogues of Three Different Merino Stud Flocks for Rams Born in 2020 TRAIT (ASBV)

STUD 1

STUD 2

STUD 3

Yearling clean fleece (%)

20.3

28.6

14.1

Yearling fibre diameter (µm)

−0.8

−2.0

−2.9

Yearling body weight (kg) Early breech wrinkle (scored 1 to 5) Worm egg count (%) Weaning rate (lambs per ewe)

9.0

4.7

3.2

−0.9

+0.6

+0.2

−43 0.18

−21 0.05

−19 0.02

Note: Only some traits are shown. A producer who is most interested in a dualpurpose (meat and wool) Merino has the best opportunity to buy an appropriate ram from Stud 1, or the best opportunity to buy a ram to produce progeny with fine wool from Stud 3. The highest fleece value, based on 2022 wool prices, will be from the progeny of a Stud 2 average ram. The differences between the progeny of an average flock ram from each stud will be half the difference between the rams’ ASBVs.

1.2.1.2.5 Information Available for Producers of Meat Lambs For prime lamb producers, ASBVs are available on the LAMBPLAN database for traits important in terminal sire breeds and in rams which will sire the dams of prime lambs. These latter values are called maternal ASBVs. One of the most important traits of a terminal sire that directly affects the commercial producer is the weight (WT) ASBV. There are marked differences in the rate of growth between lambs sired by high-WT rams and those sired by low-WT rams. Lambs sired by high-WT sires achieve market weights at younger ages, and the average weight of lambs sold at a fixed time in the growing season is greater from high-WT sires than from low-WT sires. 1.2.1.2.6 The Role of the Sheep Veterinarian in RamBuying Decisions of Commercial Producers Most sheep veterinarians are not trained in genetics and avoid involvement in decisions about the identification of a source of rams for their commercial clients. Nevertheless, familiarity with the sources of information and the powerful effect of good genetic decisions can often help guide a producer’s understanding of the options that are available. All sheep veterinarians should ensure that they are aware of the sources of information in the national genetic evaluation programmes and the very significant differences in productivity that exist between rams of high and low merit, as well as the differences in reliable information on genetic merit between the rams available from the most progressive ram breeders and those from the more conservative breeders.

1.2.2 Production Objectives 1.2.2.1 Wool Production In most commercial Merino flocks,e the production of high-value wool is the dominant objective, with income from the sale of surplus sheep being of secondary importance. A flock is considered self-replacing if all replacement ewes are bred within the flock and only rams are introduced. Very few commercial Merino flocks breed their own rams. In self-replacing Merino flocks income from wool sales constitutes 75% to 90% of the enterprise’s gross income, depending on the strain of Merino sheep and the relative values of wool and sheep-meat prices.

  The term commercial flocks refers to those flocks in which the growing and selling of wool or lambs is the primary objective, in contrast to rambreeding flocks, in which ram sales are the primary source of income.

e

7

1. 2 I m p or ta n t I n dus t ry K now l e d g e —Th e E l e m e n t s of a Sh e e p P roduc t ion Sys t e m

1.2.2.2 Meat and Wool Production

1.2.3 Flock Structure

Merino sheep of some strains, particularly the South Australian strain of Merino, are considered ‘dual purpose’, and flock owners are able to profitably sell a high proportion of their wether lambs for slaughter under 1 year of age. Some Merino flock owners join a portion of the ewe flock to rams of meat-maternal breeds (usually Border Leicester) so that income from wool is supplemented by the sale of firstcross ewe lambs or hoggets to other breeders. The firstcross wether lambs are sold for slaughter. In some flocks a portion of the ewes are mated to terminal breed sires (such as Poll Dorset), and all first-cross lambs of both sexes are sold for slaughter. The Merino ewe flock may remain self-replacing if enough ewes are mated to Merino rams to breed sufficient Merino ewe lambs to replace cast-for-age ewes. Income from wool sales and from the sale of sheep may be about equal in dual-purpose flocks.

The terms ‘flock structure’ or ‘flock composition’ refer to the age and sex structure of the flock. A self-replacing Merino flock, for example, may consist of four age groups of breeding ewes (aged 2, 3, 4 and 5 years at lambing), one age group of mixed-sex hoggets (aged 1  year), a variable number of age groups of wethers and a flock of mixed-age rams, typically aged 2 to 5 years (Table 1.3). By contrast, a prime lamb-producing flock may consist simply of five age groups of breeding ewes (2 to 6 years) and a ram flock. It is helpful to the veterinarian’s understanding of the operation of a sheep flock to have a model of the likely flock composition in mind when discussing flock-wide health problems with a flock owner. For example, when asking a client about the logistics of a footrot control programme, it is useful to ask about the management of each class of sheep on the farm separately. Informed questioning provides the most useful information and helps develop the sheep producer’s confidence. Planning for worm control programmes by incorporating grazing management also requires awareness of the flock composition. Such planning may even lead to suggestions to change the flock structure. For example, with reference to Table  1.3, keeping 300 wethers for another year, rather than selling them as hoggets, may provide one more paddock of low worm egg contamination to facilitate worm control in weaner sheep. Keeping extra wethers is likely to require a reduction in ewe numbers (perhaps 150 fewer ewes) and a comparison of the benefits gained against the income lost may or may not indicate that to be a good decision.

1.2.2.3 Meat Production The specialist sheep-meat producer has a flock of ewes which, in Australia, most commonly comprises first-cross (Border Leicester × Merino) ewes. The first-cross ewes are mated to a terminal sire and all lambs (referred to as second-cross lambs) are sold, usually before the age of 8 months. Ewes enter the breeding flock at 19 months of age or, if very well grown, 7 months of age, and are cast for age at 6 or 7 years of age. Replacement ewes are purchased either as lambs or hoggets, and all rams are introduced. Second-cross lambs are also called prime lambs. In prime lamb flocks the chief objective is to concentrate on income from the sale of lambs, but in many flocks—depending on the breed of ewe—significant income is still derived from the sale of wool and cast-for-age ewes. In those flocks using composite short-wool breeds and breeds which do not need shearing income is derived only or principally from the sale of lambs and adult sheep for slaughter.

1.2.2.4 Ram-Breeding Flocks Ram-breeding flocks include stud flocks, in which the sheep are registered with a breed association, and non-registered flocks. The large majority of rams produced are sold to commercial producers to use as flock rams, and a smaller proportion are sold to other ram-breeders. The production objectives in ram-breeding flocks differ in emphasis from those of commercial flocks, reflecting the high value to the business of income from the sale of rams. Biosecurity and strict health monitoring strategies are critically important in ram-breeding flocks. The financial ramifications for a ram breeder of selling one or more rams with, for example, footrot or lice, may be very high, and the reputational damage may have long-term negative effects.

Table 1.3 An Example of the Flock Composition at Shearing in December of a June-Lambing Self-Replacing Merino Flock Joining 1000 Ewes and Retaining All Wethers and Cull Ewe Hoggets to 18 Months of Age MIXED- HOGGETS 2.5 3.5 4.5 5.5 SEX (1.5 YRS) YEARS YEARS YEARS YEARS LAMBS OF AGE OF AGE OF AGE OF AGE Ewes

420

400

Wethers 420

400

Rams

50

255

244

235

225

48

45

43

14

Note: 1. A total of 50 rams have just been purchased to replace cast-for-age rams which will be sold after shearing. 2. A  total of 840 lambs with 5 to 6 months of wool growth and 1909 adult sheep (12 months of wool growth) will be shorn. 3. A total of 400 wether hoggets, 150 cull ewe hoggets, 225 cast-for-age ewes and 50 cast-for-age rams (aged 4.5 and 5.5 years) will be sold off-shears.

8

CHAPTER 1: Veterinary Services to Sheep Farms

1.2.4  Stocking Rate The stocking rate of a sheep flock on a sheep farm is the number of sheep grazing per unit of area (acre or hectare). As the land area is a fixed resource on a farm, the number of sheep which can be grazed is a key determinant of the income—and profitability—of the farm. The productivity of the land—the annual production of sheep feed—and the efficiency with which the feed is used by the sheep are the two critical elements in establishing the best stocking rate for the farm. When stocking rates are too low, the sheep have high levels of feed intake, but the feed resource is used inefficiently and productivity and profitability per hectare are lower than the optimum values. When stocking rates are too high, the sheep have much reduced feed intakes and, while productivity per hectare may be high, profitability per hectare is less than it could be. Productivity in this sense includes wool production, number of lambs born and reared, weaning weights, growth rates and other parameters. The quantity of all of these products from (1) each sheep and (2) the whole farm is dependent on the stocking rate. Because stocking rate is so intimately associated with the dietary intake and, therefore, the body condition score of each sheep, it also has implications for the health and welfare of the sheep. It becomes a matter then for the veterinarian when matters such as weaner growth rates, weaner survival rates, or worm control are discussed. It may be appropriate in some circumstances to suggest to a client that a reduction in stocking rate may improve health, but one should be aware of the implications of running fewer sheep. There will be fewer sheep to shear, for example, so income will be reduced. Every control strategy has a cost, and it is important not to ignore the cost of reducing stocking rate if other strategies can achieve the same outcome at lower cost. Another example, perhaps, is one frequently ignored by producers and advisors seeking to increase the reproductive rate of a flock of ewes. Reducing the stocking rate of ewes will increase their condition score, their bodyweight and their lambing percentage. The question to be asked, however, is whether the higher rates of lambs per ewe will compensate for the fewer number of ewes. Some guidelines are suggested in Table  1.4 but are intended to be only a very broad indication of the numbers of sheep which can be carried on farms. (Note that sheep are often stocked at high rates in some paddocks while other paddocks are ungrazed. The numbers here refer to the average rates across all of a farm’s grazed areas.) The establishment of the optimal stocking rate on a farm is a complex decision. There is some more information on the subject in Chapter  6, and the interested reader is

Table 1.4  Some Guidelines for Optimal Stocking Rates on Improved, Well-Fertilised Pastures AVERAGE LENGTH OF PASTURE 50 KG MERINO 50 KG MERINO ANNUAL GROWING SEASON EWES PER HA WETHERS RAINFALL PER HA 400

5 months

2–3

6

500

5.5 months

4–5

10

600

6 months

6–8

14

700

7 months

8–10

18

Note: Both annual rainfall and the length of the growing season influence the optimum stocking rate. In ewe flocks, the time of lambing and number of multiple pregnancies also influences the point of optimisation.

encouraged to consult other sources for more information. Young et al (2022) provide a recent review.6

1.2.5  Farm Management Calendars The timing of major sheep husbandry and management events on farms (the farm management calendar) is important information to veterinarians for three reasons. First, the timing of events may be an important predisposing factor to outbreaks of disease. The clearest examples of this are the relationship between the time of lambing, the incidence of pregnancy toxaemia in ewes and the incidence of nutrition-related diseases in recently weaned lambs. Second, preventive medicine strategies, like drenching, vaccinating or footrot control, should be integrated with other management events which require mustering to save time and labour for the farm operator and spare the sheep another disturbance. Veterinarians should be prepared to take the usual management calendar into account when recommending the timing of preventive therapies. Third, the timing of particular management events can have implications for total farm productivity unrelated to occurrences of disease. Examples include the time of lambing or the time of shearing—two events for which the timing is critical to the success of the farm operation. Advice about timing of such activities is generally not considered part of the role of the general practitioner, but it does form a significant part of the work of sheep specialist veterinarians. The optimisation of the management calendar for a particular farm depends on the production objective and is complex, being influenced by environmental, health management and economic considerations. Sheep flocks may be non-breeding or breeding enterprises, and the management calendar of a non-breeding enterprise generally has much more flexibility than that of a breeding flock. On non-breeding farms, the key decision is when to shear. On

1. 2 I m p or ta n t I n dus t ry K now l e d g e —Th e E l e m e n t s of a Sh e e p P roduc t ion Sys t e m

breeding properties, the key decision is when to join, followed by when to shear. The timing of most other husbandry practices will be related to these key decisions. Bell (2010) discusses this in some depth (see Recommended Reading).

1.2.5.1 Breeding Flocks In breeding flocks there are additional husbandry practices which relate to the reproductive cycle and the management of pregnant and lactating ewes, lambs and weaners. These include some or all of the following: joining, pregnancy diagnosis, lambing, lamb marking/mulesing, weaning, culling aged breeders and classing ewe hoggets. A sample calendar for a Merino farm in southern Australia with a winter-dominant rainfall pattern and autumn lambing is shown in Table 1.5. An example for a Merino flock in northern New South Wales (NSW) is shown in Table 1.6. These calendars are, of course, incomplete. Not considered are other topics which are time-critical, such as: (1) nutritional management of ewes to regulate condition score at joining and lambing, (2) management of the

Table 1.5 Hypothetical Management Calendar for an Autumn-Lambing Merino Flock in Southern Australia (Winter Rainfall Zone) ACTIVITY

TIME

COMMENTS

Joining

December– January

For 6 weeks from 1 Dec

9

previous year’s drop of young sheep and (3) worm control, blowfly control and other essential husbandry activities. The calendars in Tables  1.5 and 1.6, although fairly typical, are not necessarily the most suitable for all Merino properties. The optimisation of individual calendars includes further examination of topics such as stocking rate, seasonality in pasture quantity and quality, reproductive performance and the availability of markets for lambs, weaners and other surplus sheep.

1.2.6 The Business Aspects of Sheep Farming While some sheep flocks are run as hobbies by their owners, most sheep are run under commercial conditions, with profitability and long-term financial security as the principal aims of the business. Sheep producers operate their sheep production businesses believing that the system they choose is the best way to use the resources they have available—their own skills and interests, their labour, their land and the fixed assets attached to the land. Sheep production systems, however, are flexible and can be adapted to take advantage of changing market conditions—conditions such as the cost and availability of labour, the cost of maintenance of buildings and other assets and the prices paid and received for replacement stock and sale stock.

Crutching

February

Shear rams

Table 1.6 Hypothetical Management Calendar for a Spring-Lambing Merino Flock in Northern NSW (Summer Rainfall Zone)

Scanning for pregnancy Vaccinating all ewes

February

Scanning 6 weeks after joining ends Pre-lambing booster

PRACTICE

TIME

COMMENTS

Joining

March–April

For 5 weeks from 1 March (inside the breeding season)

Lambing

May–June

Lambs over 7 weeks

Marking mulesing and vaccinating lambs

Late June

Lambs 1 to 8 weeks old

Weaning lambs

Early September

At 3 months of age

Pre-shearing crutching

Early September

Ensure clean wool at shearing

Shearing

September

All sheep including rams

Classing ewe hoggets

September

Before or at shearing

Purchasing rams

September

Ready to join in December

Selling cull hoggets, CFA ewes, CFA rams

October

Isolating rams from ewes

October

Selling wether weaners

November

6 to 8 weeks before joining Alternatively, wethers may be retained

Scanning for April pregnancy Pre-shearing crutching

Scanning 6 weeks after joining ends Ensure clean wool at shearing

Shearing

June

All sheep including rams

Lambing

August–September Lambs over 5 to 6 weeks old

Marking mulesing and Late September vaccinating lambs

Lambs 1 to 7 weeks old

Weaning lambs

Early December

At 3 to 4 months of age

Purchasing rams

December

To use in March

Crutching

January

Shear rams

Classing ewe hoggets

January

Selling cull hoggets, CFA ewes, CFA rams

February

10

CHAPTER 1: Veterinary Services to Sheep Farms

1.2.6.1  Gross Margins for Different Sheep Enterprises Most government departments of agriculture (or equivalent) in each state of Australia produce sets of documents each year which are intended to assist graziers fine-tune their enterprises. The documents are annual gross margin budgets—statements of the expected income and variable expenses for sheep-grazing enterprises with a range of different production objectives. Gross margin budgets are intended to guide producers when comparing the financial merits of different systems but can also provide insights for advisors about the relative importance of components of a farm business’ set of accounts and the challenges facing producers in operating a profitable business. A summary of the ‘bottom lines’ of some of the gross margin budgets produced by the NSW Government Department of Primary Industries for 2022 is shown in Table 1.7. The data show that, in 2022, a sheep producer

Table 1.7  A Summary of the Expected Gross Margins of Different Sheep Enterprises in 2022, Produced by the NSW Department of Primary Industries

with a breeding flock could expect a gross margin from sheep production in the range of $70 to $130 per ewe, depending on the enterprise type. Profit per ewe is substantially less than this—the fixed costs of operating a farm (such as interest costs, insurance, permanent labour, rates and administrative costs) are not included in the set of expenses in gross margin budgets.

1.2.6.2  Animal Health Costs Animal health costs form a minor but significant proportion of the costs for sheep enterprises—typically around 15% of variable costs and a lower percentage of total costs. Other major variable expenses include wool harvesting and marketing costs (for enterprises other than those with wool-shedding breeds), pasture maintenance, supplementary feed and ram purchases. The major animal health costs include the costs of anthelmintics, external parasite control products and vaccines.

1.2.6.3  Profitability after Considering All Costs

Note: Gross margin is not profit. The expenses included in gross margin budgets do not include fixed costs. The interested reader is encouraged to seek further explanatory information from the NSW Government website.f The figures in brackets describe the average fibre diameter of the wool produced by the adult sheep in the flock; 20 µm is classed as fine-medium wool. About half of the Australian wool clip is 20 µm or finer. These budgets are prepared using a model of a farm in the medium-to-highrainfall country of the NSW Slopes and Tablelands, running 10 dry sheep equivalents per hectare.

While gross margin budgets allow an examination of the variable costs of sheep enterprises, they do not indicate directly the financial environment under which most commercial sheep farms operate, with debts to service, farm families to support and assets to replace as they wear out. Figures produced by ABARESg provide more information. To illustrate, for the three years of 2017 to 2019 inclusive, farm business profits for medium-scale lamb-producing farms in Australia ranged from $31,000 to $148,000, providing a rate of return on the capital invested in the business of 1.1% to 3.2%.7 Medium-scale farms are classed as those producing and selling 500 to 2000 lambs per year. Farms of this scale comprise 51% of Australian lamb-producing farms and produce 54% of Australian lambs for sale and their scale, and, consequently, the financial circumstances of their operators could be considered typical for Australian sheep farming. The figures produced by ABARES are averages, and there is very substantial variation in profitability between farms of similar types. Data from anonymous individual farms presented in the Victorian Livestock Farm Monitor Project demonstrate very wide differences in profitability between similar farm businesses within one region.8 Differences occur for numerous reasons, but the variation in the management skills of the operators is an important controllable factor. Veterinarians working with sheep producers have a role in improving and maintaining the financial security of farm businesses owned by their clients. It is not

f  https://www.dpi.nsw.gov.au/animals-and-livestock/sheep/sheep-gross-mar gin-budgets

g  ABARES. Australian Bureau of Agricultural and Resource Economics and Sciences.

TYPE OF ENTERPRISE

GROSS MARGIN PER HECTARE (AUSTRALIAN DOLLARS, $)

First-cross ewes, terminal rams

265

79

26

Dorper ewes, Dorper rams

429

119

43

Merino ewe (20 µm), 430 terminal ram

71

31

Merino ewe (20 µm), 406 maternal meat ram

112

41

Merino ewe (20 µm), 400 Merino ram

93

40

Merino ewe (18 µm), 632 Merino ram

133

63

Merino wethers (18 µm)

—

40

402

GROSS MARGIN PER EWE ($)

GROSS MARGIN PER DRY SHEEP EQUIVALENT ($)

1.3 I n v e s t ig at ions of D i s e a s e or Po or P e r f or m a nc e i n a Sh e e p Fl o c k

11

appropriate (in most instances) for veterinarians to attempt to provide financial advice, but a sensitivity to the financial pressures facing sheep producers and an awareness of the importance of providing advice based on economicallysound, evidence-based principles are important attributes for all livestock veterinarians.

of two sheep, and there may be some resistance to the veterinarian unilaterally deciding to extend the visit and the cost without apparent reason or agreement in advance. The extended visit might have to wait until a short initial visit is completed; much depends on the client and his or her confidence in the sheep expertise of the veterinarian.

1.3  INVESTIGATIONS OF DISEASE OR POOR PERFORMANCE IN A SHEEP FLOCK

1.3.1.2  Step 2: The Farm Visit and History Gathering

1.3.1  Structure of the Investigation Sometimes, veterinarians are asked to investigate a specific problem by the flock owner. The most common conditions which give rise to these requests are: • Poor reproductive rate • Outbreaks of disease with significant mortality • Diarrhoea • Lameness • Fleece derangement At other times the request may be more general, such as a request to investigate: • Poor growth or unexpectedly poor body condition in adults or young sheep • Weaner ill-thrift Occasionally a producer may make a request specifically for a preventive medicine programme. The most likely trigger for this is concern about control of internal parasites and anthelmintic resistance management, but it could also include a producer’s concern about a vaccination programme, or nutritional supplementation, including trace element and vitamin nutrition.

1.3.1.1  Step 1: Making Intentions Clear with the Client The veterinarian should arrange a time to visit the farm and have an agreement in advance with the client about what is to be examined and how long the visit might take. If the visit requires the collection of a detailed history or an inspection of a number of sheep or groups of sheep at the pasture, the client should be made aware that there is an hourly charge for the visit and should be advised of its likely cost. In general, clients appreciate that it is necessary to spend 2–4 hours to become sufficiently familiar with the farm and the sheep and to gather a good history. It is necessary, however, that the length and thoroughness of the farm visit is aligned with the client’s expectations. For example, the producer may be expecting a visit and quick necropsy

During the farm visit the veterinarian should gather both a history and a sense of the owner’s understanding or prior experience of the problem. If the scope of the request is broad, the history gathering should be comprehensive. If the request is specific, then the questions should clearly relate to the problem at hand. For example, if the veterinarian is requested to investigate an outbreak of lameness, then the history collection should relate to that condition in the first instance at least. After some animals have been examined and the diagnostic possibilities have been narrowed, further history collection will be important, but the owner should be made aware of the relevance of the questions. In contrast, if the investigation is to address a problem which is less well defined and more obviously a complex issue, such as the investigation of a poor reproductive rate, it is wise to spend an hour or so collecting history and reviewing records before inspecting or examining any sheep. So, depending on the particular situation, the history collection could include: 1.3.1.2.1  Signalment of the Affected Animals Determine which sheep are affected and which are not, with groups being defined by their age group, sex, management group, reproductive status and breed. 1.3.1.2.2  The Timing of Events, Relating to the Time of Year, Climatic Events, Any Husbandry Procedures Determine when the condition first became noticeable and attempt to relate that to shearing, crutching, joining, drenching, moving from one pasture to another or any other management events. Determine whether the problem has happened on previous occasions. 1.3.1.2.3  Relationship to Introductions Is the affected group a purchased or a home-bred mobh? If introduced, the time and source of the introduction should be noted.

 A mob is a flock of sheep run in one paddock, often of the same age and sex, and subject to the same, or very similar, husbandry. The entire sheep flock on any one farm usually consists of multiple mobs. h

12

CHAPTER 1: Veterinary Services to Sheep Farms

1.3.1.2.4  Gathering Some Basic Epidemiology The problem should be quantified, if possible, based on the number of sheep in the flock and in affected groups, their sex, age and other identifying factors. The number affected, number of sheep dying and the time sequence and pattern of disease occurrences should be recorded. 1.3.1.2.5  Gathering the General Management History This should include joining and lambing dates, length of joining, shearing and crutching dates, weaning dates, normal drenching and vaccination dates. 1.3.1.2.6  Gathering the Specific Management Information The details of anthelmintics, vaccines, supplementary trace elements and vitamin nutrition should be collected, including products, dosages and frequency of treatment. 1.3.1.2.7  Gathering the Nutritional History In addition to trace element and vitamin supplementation, other supplementary feeding programmes should be noted. If hay, grain or silage is used, the amount provided and the frequency of feeding should be noted. Supplementary feed should be calculated as a daily rate per head, in grams. Other information relating to specific problems which should be collected with the history is discussed in more detail in the chapters dealing with particular syndromes. For example, you may need to know much more about fertiliser treatments, the source and health status of introduced sheep, stocking rates, nutritional supplements, parasite control approaches and other management interventions, depending on the problem being investigated. The information gathered should be recorded for future reference. Usually, taking contemporaneous notes is best. By the time the history is collected, much more should be known about the context of the problem—the flock size and type, the management system, the animals affected, the broad nature of the problem—but also a sense of the owner’s skill and experience and an appreciation of the persistence of the problem. It is important for the veterinarian to decide, for example, if the producer is a very able and experienced person who has battled the problem for years, finally calling in the veterinarian for assistance, or if this is a first-time occurrence of a relatively minor or straightforward problem. Elucidation of the intransigence of the problem and the ability of the producer will provide an indication of the expected scope of the investigation.

1.3.1.3  Step 3: The Environment If and when appropriate, the veterinarian should ask to be taken to see the sheep at pasture. This may involve an inspection of all of the different mobs on the farm or just a sample of the mobs. Inspecting the sheep at pasture also provides an opportunity to review the infrastructure of the farm. The veterinarian should note the quality of the sheep-handling facilities and the existence or not of a laneway system for moving sheep to and from the handling yards. Pastures should be inspected to determine if they are improved, well fertilised and relatively weed-free. The current state of the pastures in terms of proportion of green or dry and the availability should be noted. Pasture availability may also provide some insight into the intensity of stocking of the pastures, particularly if pastures are set-stocked rather than rotationally grazed. Watering points should also be inspected to determine the ease of access of sheep to good-quality drinking water.

1.3.1.4  Step 4: The Sheep at Pasture The sheep should be examined as a flock undisturbed at pasture. Examination should include both the affected groups and at least some of the non-affected groups. If possible, the mobs should be inspected first with relatively little disturbance and with any sheepdogs remaining restrained. Some lameness conditions are best assessed when the sheep are walking quietly or grazing rather than when they are moving quickly. The mob should be observed as a whole in order to decide whether some animals have separated from the mob or are behaving differently from their flockmates. After inspection without disturbance the mob can be gathered, provided it is safe to do so. Ewes with young lambs should not be disturbed, if possible. Moving the sheep to close-by yards or to another part of the paddock will enable an assessment of exercise tolerance and lameness. Coughing may not be apparent in some cases until the flock is made to move quickly for a short distance. Presenting signs such as diarrhoea (based on the presence of dags), lameness and fleece derangement are readily evident from an inspection of the mob at pasture and a rough estimate of prevalence can be made. The general health and condition of the sheep can also be assessed by observing the fullness of the abdomen, or an obviously very large range in size or condition. In the case of lambs, healthy, well-fed lambs are strong, running quickly and playing, while unhealthy, underfed lambs adopt a more sedate or plodding form of walking. The bloom on lambs which are still on their mothers provides an indication of the quality of the lactation of the ewes. It is possible to catch individual sheep in the field. Usually, a producer with a capable sheepdog can hold a mob

1.3 I n v e s t ig at ions of D i s e a s e or Po or P e r f or m a nc e i n a Sh e e p Fl o c k

in a corner of a paddock while one or more sheep are caught for closer examination. If this is done, it is essential that the corner has sound fencing and does not include a boundary fence. If the sheep press onto the fence and break through into a neighbour’s paddock, the veterinarian may be deemed at least partly responsible for the biosecurity failure. It is possible to complete this section of the flock workup by inspecting the flock or a selected mob in the sheep yards. This is generally not as satisfactory as examination at pasture because behaviours can be dramatically changed by the stress of mustering. Lameness, for example, may be much less evident in the yards than when the sheep are inspected without disturbance in the field. Nevertheless, when a flock or mob is confined in a yard it is much easier to catch multiple individual sheep for more detailed examination.

1.3.1.5  Step 5: Individual Examination of the Sheep In most instances, after the sheep have been examined as a group, individual sheep need to be examined in order to either confirm a diagnosis or to provide further clinical evidence, or specimens, so as to help arrive at a definitive diagnosis. The technique for clinical examination of the individual sheep is described elsewhere (for example, Jackson and Cockcroft (2002)9 and Lovatt (2010).10 1.3.1.5.1  Body Condition Scoring and Body Weighing Body condition scoring (see Section 1.5) is best done with a group of sheep standing in a race. It is often useful to condition score a random sample of the flock (20 to 30 animals), record the scores and calculate an average. A  simple way to do that is to create a histogram, which shows quickly and visually the range and average of the scores. Condition scoring provides an instant assessment of the nutritional status of the sheep and can be used as a basis for continuing monitoring. The condition score should be related to the current physiological state of the animals. For example, a mean condition score below 2.0 of a group of late-lactation, twin-raising ewes may be acceptable and normal. The same condition score in late pregnancy could well be associated with a high risk of pregnancy toxaemia, high lamb mortality or long-term negative effects on the productivity of the progeny. Weighing a sample of the flock can also be useful as a basis for monitoring, but without a benchmark or a second weight for comparison it is not possible to use bodyweight alone as a diagnostic clue for adult sheep. For young sheep body weighing can be very useful, particularly when compared to the reference weight for adult sheep of the same

13

genotype. For example, the mean body weight of a group of weaned Merino lambs can be very informative about the risk of malnutrition and death as a result of poor feed quality. 1.3.1.5.2  Collecting Specimens from a Sample of the Flock Specimens are frequently collected from live sheep to aid the diagnostic process. Tissues typically include blood (for biochemistry such as trace element nutrition, and for immunology such as the detection of rising titres to infectious disease, as well as for proving disease freedom) and faeces for parasitological diagnosis. It is important that sufficient numbers of animals are sampled in order to produce dependable results. The more animals that are tested from the one management group, the more reliable is the estimate of the mean value (Figure 1.1).11 For very variable parameters, such as faecal egg counts, 10 is the lowest number of animals that should be sampled to usefully estimate the mean value for the group from which the sample of animals was derived,12,13 and higher numbers (15–20) are usually recommended. The higher the number tested, the narrower the confidence interval around the estimate. Note that the confidence interval around the estimate of a mean is, for large populations and small sample sizes, independent of the population size. It is misleading to suggest that an appropriate sample size can be based on a percentage of the population—it is the absolute size of the sample that matters, not the size of the population from which the sample is drawn, nor the relative size of the sample compared to the whole population. One should choose an appropriate sample size based on the desired level of accuracy and the degree of variability within the population (the standard deviation) using standard and straightforward statistical formulae. Remember what confidence intervals tell us—in the case of 95% confidence intervals, we are 95% confident that the true population mean lies within the range specified. Another way to consider this is that, if we took 100 samples and estimated the mean and 95% confidence limits each time, we would expect that the true mean would lie within that range on all but five occasions. 1.3.1.5.3 Necropsy Necropsy of sheep is a very valuable diagnostic tool, and the opportunities it presents should not be wasted by poor techniques or lack of specimen collection for expert review in a diagnostic laboratory. The sheep chosen for necropsy should be recently dead or sacrificed on the basis of advanced clinical signs. Multiple necropsies are advisable—three animals with consistent evidence of

14

CHAPTER 1: Veterinary Services to Sheep Farms

Figure 1.1  An illustration of the relationship between sample size and the confidence intervals (ci) for an example of glutathione peroxidise (GPx) measurements in lambs, used as a guide to selenium nutrition status. Paynter et al. (1979)11 found that groups of lambs from different flocks had mean GPx levels ranging from 10 to 50 units per gram of haemoglobin but that only flocks of lambs with mean levels below 30 responded with increased growth rates if supplemented with selenium (i.e. 30 could be considered the threshold for diagnosing selenium deficiency). In their study, the standard deviation of values within each group of lambs tested was variable but around 15. This graph tells us that, for a standard deviation of 15, 95% confidence intervals could not be considered ‘acceptable’ unless 10 lambs or more have been tested. If we test only 10 lambs, then we are 95% confident that the true mean lies within a 21.4-unit range (95% ci for n = 10 is ± 10.7). With fewer than 10 lambs tested we may not be sufficiently confident that the result will be useful to the client unless the sample mean is approaching an extreme value. The figure is a graph of n against t n−1(0.95)·s/√n where s is the sample standard deviation and the value for t n−1(0.95) can be found from tables of the t distribution or using the Microsoft Excel® function T.INV.2T (0.05, n−1). Source: Kym A Abbott.

similar syndromes give much more compelling evidence than just one animal. Every opportunity to collect tissues for further examination should be made—including the gastrointestinal tract for total worm count (faecal egg counts are not useful in one animal or animals in ill health), liver sections for trace element assays and a full set of tissues for microbiological and histopathological testing— including the brain.

• Improves animal welfare • Improves the owner’s confidence in the disease management capacity of the farm staff • Permits the owner or manager to embark on strategies which will increase the flock’s productivity, such as increased reproductive rate or increased stocking rate, knowing that good animal health can be maintained under changing conditions

1.4  DEVELOPING A FLOCK HEALTH PROGRAMME

The essence of a flock health programme, and the way that it differs from ‘fire-brigade’ veterinary services, is that the veterinarian plays a role in identifying the ways in which health, welfare and productivity can be improved, rather than responding to a request for veterinary intervention from the owner.

1.4.1  The Reasons for a Flock Health Programme A flock health programme is a structured set of veterinary services aimed at improving the health, welfare and productivity of a flock of sheep. A programme will be acceptable to the flock owner if it • Reduces the cost of disease conditions in the simplest and lowest-cost way possible • Increases farm production and profitability

1.4.2  Delivery of the Programme The successful delivery of a programme requires the veterinarian to have a level of knowledge of sheep medicine, the sheep industry and sheep husbandry practices well beyond that of the very recent graduate, although those graduates with sheep-farming backgrounds usually have an

1.4 D e v e l opi ng a Fl o c k H e a lt h P ro gr a m m e

advantage. Some of the relevant attributes are described as ‘Level 2’ skills and knowledge in the opening section of this chapter. Some elements of a flock health programme which can be successfully delivered by a veterinarian with Level 2 knowledge and experience are listed in Table 1.8. The disease conditions that are listed are common and endemic on many farms, or at a high risk of occurrence on most farms,

15

and of course there are many other conditions which occur sporadically. It should be noted that: 1. It is not necessary to deliver the whole programme. Any one element of the programme can be a starting point and may be the only element provided on any particular farm. For example, the client may only want a ‘package’ aimed at better worm control or reliable trace element nutrition.

Table 1.8 An Example of a Flock Health Programme for Level 2 Veterinary Involvement THE ELEMENTS OF A FLOCK HEALTH PROGRAMME Data collection Flock size, flock structure Buying and selling strategies Farm calendar Risks from neighbours Internal parasites Establish a programme to understand the farm’s helminth epidemiology Establish a monitoring programme Make grazing management plans Establish the farm anthelmintic resistance status Develop an anthelmintic use plan External parasites Lice detection and plans to eliminate if present Flystrike prevention plans Vaccination programme Clostridial, CLA, CPD, OJD may be routine Erysipelas, Campylobacter vaccines may be appropriate Identify what should be used and when it should be used Trace element status Se, Co, Cu, I status should be ascertained but informed by knowledge of regional status Plan to establish any need and treat effectively Reproduction Ram team health and genital soundness examinations. Ewe productivity—reproduction rate, scanning may be appropriate and, if so, used effectively Supplementation of ewes and weaning policies (age of lambs, management of lambs) Animal welfare standards Lamb marking strategies and pain relief Weaner health If weaners are retained on the farm over summer and autumn, is a supplementary feeding plan in place? Biosecurity procedures How to identify safe sources of sheep Quarantine procedures on introduction How to avoid introducing lice, footrot, OJD, brucellosis and anthelmintic-resistant parasites Farm dog health Ensure dogs are vaccinated appropriately and dewormed appropriately

NOTES These data are primarily collected so that advice fits the needs of the production system, rather than as a way to identify problems in flock management.

A veterinarian’s understanding of each farm’s challenges in worm control develops over several months of monitoring worm egg counts, anthelmintic efficacy, and the availability of grazing management to aid control.

Lice: establish freedom from infestation. Flystrike: to minimise the incidence of strikes and eliminate the risk of a fly wave. Some vaccines should be given routinely, but others may only be justifiable if the risk of disease is significant.

In some cases producers are treating unnecessarily, and in some cases ineffectively. If a need for supplementation is identified, the most appropriate and effective methods of supplementation should be used. Examination of the health and genitalia of the ram team, including annually, before ram purchases, is recommended. Monitoring ewe nutrition through joining, pregnancy and lactation may be useful for some clients.

Advice about pain management, and supply of appropriate products, should be a part of every flock health plan. If the weaner mortality rate is elevated, a preventive programme can be very cost effective. Clear written policies should be developed to remain free of diseases that could be imported in purchased sheep.

Metacestode infestations are a threat to meat-sheep sales.

16

2.

3.

4.

5.

6. 7.

CHAPTER 1: VETERinARy SERViCES To SHEEP FARmS

The data collection step is still useful but may be limited to only the necessary information for the work in hand. The delivery of the programme, or parts of the programme, may commence because problems have arisen in one of the listed elements (for example, an outbreak of helminthosis) or as a consequence of a disease investigation into an unlisted element (footrot outbreak, redgut deaths, etc). The visit provides the veterinarian an opportunity to assess the client’s skills in animal health management and, if appropriate, to offer further assistance. The essence of a ‘programme’ is that there are intentions of repeated visits—for monitoring, for specimen collection, for veterinary procedures. Each re-visit should be planned in advance and a date agreed, or a date for a call to book it confirmed. It is important not to over-service. During the period of establishing credibility with the client it is important that there is clear evidence of ‘good value’ for the consulting fees. The first clients should be chosen carefully—the producers who will make the best use of the veterinarian’s good advice are the ones who are already operating at a high level. Less able flock managers often make mistakes in implementing good advice. Moving to an annual retainer fee, with a prescribed number of visits, is possible, but not essential. The veterinarian should keep written records of each visit, including results of all tests and all plans made for the client’s action. It is very wise to ensure the client has a copy of the same agreed set of plans.

1.5 BODY CONDITION SCORING AND ITS RELATIONSHIP TO PRODUCTIVITY Body condition scoring (BCS) is widely used in sheep production systems in Australia, New Zealand and many other countries. The technique classifies sheep on an ordinal scale of 0 to 5, although score 0 is rarely used and most operators consider the range only from 1 to 5. 14 15 The system allocates individual sheep a score based on the degree of fat and muscle mass palpable over the lumbar vertebrae while the animal is restrained in a standing position. The amount of soft tissue between the skin and the vertebrae is related to the amount of fat stored in the whole body and is therefore an indication of the recent past nutritional level of the animals and its ability to meet demands for endogenous energy supply if required in the immediate future. The five scores are described and illustrated in Table 1 9 Modifications of the five-score system include the use of half-scores or the use of ‘+’ or ‘−’ attached to each score.

Table 1.9 Description of the Five Scores Used in Body Condition Scoring of Sheep DESCRIPTION OF SCORE

Score 1. The dorsal spinous processes are prominent and sharp, and fingers can be placed deeply between them. The transverse processes are sharp, and fingers pass easily and deeply under the ends and between each process. The eye muscle (red) is flat and has no fat cover. Score 2. The spinous processes are prominent but not sharp. Fingers can be depressed between them but not deeply. The transverse processes feel smooth and rounded, and fingers can be pressed under the ends and between the processes but not deeply. The eye muscle has moderate depth but little fat cover. Score 3. The spinous processes are palpable only as projections and are smooth and rounded. The transverse processes are smooth and well covered, and firm pressure is required to feel under the processes or between their ends. The eye muscle is full, with moderate fat cover. The general feel across the loin is of smoothness and fullness. Score 4. The spinous processes can only be detected with pressure between the fat cover on either side of the centreline. The transverse processes are difficult to detect. The eye muscle is full and has a thick fat cover. Score 5. The spinous processes cannot be detected even with firm pressure. The skin dips down between the fat on either side of the centreline towards the spinous processes. The transverse processes cannot be detected. The back of the sheep is flat and broad. There are large fat deposits over the rump and tail. Source: Russel (1984)15

CROSS-SECTIONAL DIAGRAM OF LUMBAR VERTEBRA SHOWING EYE MUSCLE (RED), BONE (BLACK) AND SKIN (BLUE).

1.5 B ody C on di t ion S c or i ng a n d It s R e l at ions h i p t o P roduc t i v i t y

The difference in bodyweight of an adult Merino sheep for a change of one BCS is about 19% of its body weight at a BCS of 2.5. For example, for a sheep which weighs 50 kg at BCS 2.5, one score represents approximately 9 kg, although there is variation between sheep in the ratio of one score to bodyweight.16

1.5.1  Usefulness of Body Condition Scoring The change in bodyweight accompanying the change in fat reserves can also be monitored in sheep by repeated weighing. The use of scales provides a more objective measure of bodyweight, but it does not provide a direct estimate of changes in fat reserves in animals that are growing (their frame size may have increased since they were last weighed) or in animals that are pregnant (the change in mass of the uterine contents is unknown). The advantages of body condition scoring are that it measures the fat reserves of an animal directly (within the bounds of its accuracy) regardless of other changes in body composition, that it can be used to compare the nutritional state of animals of different type regardless of their frame size and that it requires no equipment.

1.5.2  Reliability of the Technique There is a high degree of subjectivity involved in scoring, but with experience and practice, a person can attain a high level of repeatability in measuring BCS, providing a high level of intra-assessor reliability. Body condition scores are widely used in published industry guidelines and recommendations for producers and advisors, so it is important that there are also high levels of interassessor reliability. There are often opportunities at field days or on-farm meetings for veterinarians, advisors and producers to compare their scoring technique, and veterinarians should take all opportunities to compare their techniques to those of others and modify their scoring if necessary.

1.5.3  Relationship of Body Condition Score to Health and Productivity There is a relationship between the body condition score of a Merino ewe and its productivity: higher BCS at joining increases fecundity, and higher BCS at and after day 100 of pregnancy increases wool production, lamb birthweight and lamb survival rates.17,18 Knowledge of these relationships provides an opportunity for sheep producers to predict the effect of the nutritional state of the ewes on the productivity of the flock and, if necessary and likely to be cost effective, take steps to intervene in the current season or manipulate grazing and feeding

17

conditions to produce better outcomes in subsequent seasons.

1.5.4  Relationship of Body Condition Score to Welfare The BCS of a sheep reflects both its nutritional history and its health. One of the key signs of poor welfare of sheep, either due to under-nutrition or disease, is a low BCS. A score < 2 should raise concerns about an animal’s welfare, and a BCS 43 °C soon after death), pathognomonically pink and dry muscles, red and congested lungs and a small contracted heart.70 Heat stress can cause production losses in sheep. Heat stress in pregnant ewes is associated with reduced lamb birth weight and survival.74 Other reproductive effects of heat stress include a reduced incidence of oestrous, reduced lambing rates, increased embryo loss, reduced pregnancy rate and reduced ram fertility.74 Heat stress has also been associated with decreased milk yield, milk fat and milk protein.71

Figure 2.2  Sheep in a yard crowd into a small area of shade on a sunny day. Providing enough shade for all sheep to use during warm weather is important to minimise the risk of thermal discomfort and heat stress. Source: Natalie Roadknight.

Reducing the risk of heat stress involves the provision of shade, access to cool drinking water, avoiding handling of sheep during hot conditions where possible and shearing prior to the onset of hot weather (Figure  2.2).70,71 In closely confined sheep, fans can reduce heat stress risk.71 In hot and dry weather, application of water to sheep or pens can reduce heat stress risk, but if humidity is already high, it can increase heat stress.71 Nutritional strategies are becoming an area of focus for the reduction of heat stress in livestock.71 Longer-term strategies may involve selecting more heat-tolerant strains or breeds.71

2.5.2  Cold Stress The sheep at highest risk of cold stress are young (especially newborn) lambs and newly shorn sheep. In some newly shorn sheep flocks, mortalities as high as 90% have

30

CHAPTER 2: Welfare of Sheep

been recorded due to cold exposure.75 Post-shearing mortalities can even occur in summer, as sheep are not adapted to the cold at this time of year.75 Sheep can be at a higher risk of mortality from cold exposure for up to 28 days after shearing.75 For neonatal lambs, wind plus wet coats (due to being just born or from rain) pose a high risk of cold stress even in relatively moderate temperatures.76 Cold exposure, when prolonged, can cause a characteristic peripheral oedema which is identifiable at post-mortem examination.76 Peripheral oedema is not present in all cases of death when cold exposure is a contributing factor.76 Prevention of cold stress involves provision of shelter from wind and rain, careful timing of shearing and lambing to avoid cold or wet weather/seasons where possible and good dam nutrition to improve lamb birth weight and optimise colostrum availability.76

2.6  WELFARE IMPACTS OF KEY DISEASE CONDITIONS 2.6.1 Footrot The pain and debility associated with footrot in sheep mean that it is one of the most important diseases in relation to its direct impacts on sheep welfare. The lameness caused by the condition is directly contributed to by pain from the tissue damage involved, and research has shown that sheep with severe footrot have reduced mechanical pain thresholds that are restored by local anaesthetic blockades.77 Furthermore, the same study showed that successful treatment of the condition in moderately affected sheep restored the pain threshold to normal values, but sheep that had suffered severe footrot maintained this hyperalgesia when tested at three weeks, before recording a normal response three months later.77 Another welfare consequence of footrot in grazed sheep is that affected animals will rapidly lose body condition, as they are unable to move around and effectively graze. It is not uncommon to see footrot-affected sheep attempting to move while balanced on their carpal joints as the animals seek to graze (Figure 2.3).78 The impact of footrot is such that it has been successfully used in the development of a facial expression scale for the assessment of pain and its severity in sheep.79

2.6.2 Mastitis The presence of clinical signs of inflammation (tissue heat, redness and swelling), together with the animal behavioural response to palpation, indicates that mastitis in livestock is a painful condition. This is supported by the reported human experience of the condition, and means

Figure 2.3  Ewes with footrot in one or both forefeet may graze on the knees, presumably in response to pain on weight-bearing. Source: Kym A Abbott

that the pain and debility from mastitis in ewes have a significant impact on animal welfare.80 Similarly to footrot, chronic mastitis in sheep has been associated with a risk of hyperalgesia as measured in response to a mechanical stimulus.81 In this research, there was also an associated increase in the prostaglandin EP3 receptor in the spinal cord on the same side as the mastitic mammary gland, lending further weight to the pain impacts of sheep mastitis and suggesting that such spinal mechanisms may be implicated in a hyperalgesic response. In their work to develop a pain assessment framework for sheep using visual assessment of animal facial expressions, McLennan and co-workers studied sheep with acute clinical mastitis together with matched control ewes.79 This work showed that sheep with mastitis exhibited greater pain-related facial expressions than unaffected sheep, and that this response resolved over seven days in association with antibiotic treatment along with NSAID administration.79

2.6.3  Lambing Losses Under extensive conditions, there may often be a marked discrepancy between pregnancy scanning rates and lamb marking (or weaning) rates, with one large-scale study recording a loss between mid-pregnancy scanning and lamb marking of 36% in maiden ewes and 29% in twotooth ewes in southern Australia.82 Although some of these losses will be occurring as pregnancy losses, the worldwide estimate for neonatal lamb loss has been quoted at 15%, and average perinatal lamb mortality under extensive Australian conditions has been estimated at levels between 10% for singles and 30% for twins.83,84 Actual perinatal

2.7 Hu m a n e K i l l i ng Te c h n iqu e s a n d C onsi de r at ions

lamb losses may be higher or lower than these averages depending on environmental conditions, as well as ewe and farm management factors, but this level of mortality does prompt evaluation on animal welfare grounds.85,86 A detailed evaluation of the causes of death in neonatal Merino and crossbred (Merino × Border Leicester, Poll Dorset, Texel, Suffolk, White Suffolk, Hampshire Down and Southdown) sheep across southern Australia found that the proportions of lambs assigned to each category were starvation-mismothering (25%), stillbirth (21%), birth injury (18%), dystocia (9%), death in utero—prematurity (10%), predation (7%), cold exposure (5%), undiagnosed (4%), infection (1%) and misadventure (1%). Combining like categories, dystocia, stillbirth and birth injury were applicable to 48% of the lambs, with the authors concluding that improvements in lamb survival required a focus on reducing losses from dystocia, stillbirth, birth injury and starvation.87 Aside from any accompanying ewe mortality, the animal welfare risks associated with neonatal lamb loss and morbidity have been categorised as breathlessness, hypothermia, hunger, sickness and pain.88 Although it is not possible to measure directly, it has been hypothesised that unless the newborn lamb achieves sufficient oxygenation to overcome the pre-term adenosine-mediated inhibition of brain electrical activity, its capacity for conscious awareness (and potential suffering) may be limited.89 More moderate to severe suffering has been postulated to be a risk in situations of neonatal death through starvation, illness or injury (though dystocia or predation).88

2.6.4 Flystrike Where present, flystrike is recognised as having a major impact on the welfare of sheep. Effects on sheep may progress from skin irritation in early strike through to the pain and toxaemia associated with significant tissue damage following severe and secondary flystrikes and accompanying tissue breakdown and microbial infection. In terms of mortality, earlier data both recorded and estimated a 10% mortality among flocks of sheep subject to flystrike under Australian conditions.90,91 More recently, a detailed study of well-managed and monitored sheep flocks found a mortality rate of 2% following the establishment of strike—mainly to the breech area.92 However, mortality was associated with the severity of the strike upon detection, and individual sheep with the most severe category of strike (Category 3) suffered a 15% mortality.92 The tissue damage induced by flystrike has profound impacts on the physiology of the sheep. Moderate, experimentally-induced strike was found to induce a substantial increase in blood white cell counts (mainly through

31

neutrophils) by the second day after the initial strike, along with day 3–4 increases in pro-inflammatory cytokines (IL-6), acute phase proteins (serum amyloid A and haptoglobin) and cortisol. These changes were accompanied by significant pyrexia and inappetence.93 There is also evidence that the impacts of flystrike can continue for some time after the larval infestation has been removed. Long-term follow-up in the study by Horton and colleagues recorded that ewes that had suffered flystrike lost significant weight. Those animals that had suffered more severe strikes had reduced bodyweight for at least three months afterwards.92

2.7  HUMANE KILLING TECHNIQUES AND CONSIDERATIONS Humane killing means inducing an immediate loss of sensibility, with no return to sensibility before death supervenes. Euthanasia can be thought of as humane killing that is done in the best interests of the animal—for instance, in the case of an animal that is suffering from an untreatable and severe illness or injury. Veterinarians who treat sheep should be equipped with both the knowledge and equipment to perform humane killing. Additionally, they should be able to advise and ideally also train producers on how to perform humane killing. As a general rule, killing methods that are suitable for cattle are also appropriate for sheep.94 For firearms and captive bolt devices, proper storage and maintenance is essential for good safety and efficacy.94,95 The best technique for humanely killing a sheep will differ depending on the context. Factors that should be considered include: whether the sheep is currently conscious, the age of the animal, the killing methods available, the urgency for killing (for example, the current level of animal suffering), whether the sheep can be effectively restrained and the safety of any animals or people nearby. Different jurisdictions may regulate what killing methods are allowed to be performed, who is permitted to perform them and the circumstances they can be performed in. The following information is therefore based on the acceptability of methods from a welfare rather than a legal perspective.

2.7.1  Anaesthetic Overdose Sheep can be euthanised by veterinarians with an overdose of anaesthetic agent intravenously if they are not intended for food use. This method can be less confronting to clients than physical methods such as firearms or captive bolts, so it may be the most appropriate method for pet sheep. A barbiturate such as pentobarbital is suitable, at a similar

32

CHAPTER 2: Welfare of Sheep

dose rate to that for other species.94 Appropriate disposal of the body to avoid scavenging must be carried out.

or firearm instead and to complete any suitable training and legal requirements for their use on farm.

2.7.2 Gunshot

2.7.5  Assessing Insensibility

A gunshot of suitable calibre delivered to the appropriate position on the skull is considered capable of achieving a humane kill. The American Veterinary Medical Association (AVMA) Guidelines for the Euthanasia of Animals96 provides details about the types of firearms, appropriate ranges, the correct position to target, and the types of bullets to use in sheep. The safety of people and other animals, legal requirements and any post-mortem diagnostic requirements for an intact brain need to be considered before using this method.94

After captive bolt application, signs of insensibility (unconsciousness) in sheep include immediate collapse, brief tetanic spasm followed by unco-ordinated leg movement, immediate and sustained termination of rhythmic breathing, absence of attempts to rise, absence of vocalisation and lack of the corneal reflex.95,96,99 Agonal breathing does not indicate sensibility.95

2.7.3  Captive Bolt Devices Appropriate calibre penetrating captive bolt devices are suitable for killing sheep.96 Penetrating captive bolt devices produce insensibility by a combination of concussive force and brain damage.97 The AVMA recommends a follow-up killing method such as pithing (for animals not intended for food) or exsanguination, unless a powerful penetrating captive bolt gun designed specifically for stun-killing is used.96 Non-penetrating captive bolt devices can be used to stun sheep, followed up immediately with a secondary killing method (see Section 2.7.6). The stun-to-stick interval should be as short as possible, and less than 60 seconds.97 Good head restraint is important to facilitate correct bolt placement.97 The placement of non-penetrating captive bolt devices is less forgiving than placement of penetrating captive bolts.97 Proper maintenance and storage of captive bolt devices and cartridges is crucial for ensuring good efficacy.96 Some jurisdictions may require operators to be licensed to use a captive bolt device.

2.7.4  Neonatal Lambs Gunshots and penetrating captive bolts can be effective for killing lambs. However, they may be difficult to apply safely to small neonatal lambs being manually restrained.94 Appropriately powered non-penetrative captive bolt devices can be used as a single step killing method for neonatal lambs, using a position between the ears and behind the poll, with the lamb’s chin tucked in.98 Correct positioning is essential for this method to achieve a humane kill.95 Blunt force trauma may be legal in some jurisdictions for very young or small lambs, but it is not considered a humane killing technique due to the unreliability of inducing immediate insensibility.94,98 Sheep producers should be counselled to purchase an appropriate captive bolt device

2.7.6  Secondary Killing Methods Stunned or anaesthetised sheep can be killed by exsanguination (via a neck cut including the jugular veins and carotid arteries) or intravenous potassium or magnesium salt solutions.94,96,100 Magnesium solutions are preferable over potassium solutions as they result in less marked reflex movements after administration.100

2.7.7  Inhumane Methods Blunt force trauma, exsanguination of conscious animals, and other methods that do not cause instant insensibility or death reliably are generally considered inhumane.

2.7.8  Confirming Death Death should be confirmed using multiple criteria.96 The five-finger head check to confirm death involves checking that101,102: 1. There is no corneal reflex 2. The pupil is fixed and dilated 3. There is no jaw tone 4. The tongue is flaccid 5. There is no rhythmic breathing A lack of rhythmic breathing should be assessed last, as it can return after a few minutes in animals that are stunned rather than killed.101,102 The lack of a heart beat can be used as evidence in support of death.96 However, the presence of a heart beat can be inconclusive for the captive bolt method, as cardiac activity may continue for 8–10 minutes after application of a captive bolt if a secondary method is not used.103 None of the signs discussed earlier is sufficient to confirm death if used alone.96

2.7.9  Further Resources on Humane Killing The AVMA Guidelines for the Euthanasia of Animals96 is freely available online and has detailed information about humane killing methods, including illustrations of the

2. 8 A ss e ssm e n t of Sh e e p f ol l ow i ng Bus h f i r e s

correct position for gunshot and captive bolt placement in sheep. The Humane Slaughter Association has a number of online resources104 available, including pictures and a video link on how to correctly use a non-penetrating captive bolt on neonatal lambs.95 Dr. Temple Grandin’s website105 has useful information on humane killing techniques as well as low-stress stock handling.

2.8  ASSESSMENT OF SHEEP FOLLOWING BUSHFIRES There is limited peer-reviewed evidence available about the pathology of bushfire injuries in livestock.106 However, case studies and the previous experience of veterinarians, producers and first responders in the field can all help to inform decision making. The most common areas in livestock to be affected by bushfires are the hooves, skin and lungs.106 Particular attention should be paid to areas with non-wool-bearing skin and areas close to the ground, such as the coronary band/peripole, udder, inguinal area, scrotum, vulva and legs.106 Teats affected by burns may occlude during healing, limiting ewes’ productive life.106 Hooves burnt at the coronary band can result in hooves sloughing off days after the initial burn106, exposing the underlying sensitive tissues and thus likely resulting in severe pain. Signs of fire-related pathology may initially be subtle, and it can take several days to weeks to reveal the full extent and severity of burns.106 Because of this, any animals that are treated for burns need very careful monitoring, and clients should be counselled that euthanasia may be indicated if the extent or severity of burns turns out to be greater than initially apparent. In addition, appropriate pain relief should be provided even if burns seem relatively mild.106 Initially, bushfire-affected sheep should be clinically assessed and either humanely killed or treated and closely monitored.107 Clinical and non-clinical considerations that may inform decision making are listed in Boxes  2.1 and 2.2. Veterinarians should consider whether they are able to provide adequate treatment, including pain relief and flystrike prevention, to affected sheep. Factors which may limit veterinarians’ ability to provide adequate treatment are the drugs and materials they have on hand, the facilities available, the conditions in the field, and the ability to schedule regular revisits. Even if sheep are deemed likely to survive, if adequate treatment or monitoring cannot be provided, including if sheep are likely to endure prolonged suffering despite treatment, then humane killing may be an appropriate option.

33

Box 2.1  CLINICAL INDICATIONS FOR IMMEDIATE HUMANE KILLING OF BUSHFIRE-AFFECTED SHEEP.106,107,108 NOTE: SOME CLINICAL SIGNS MAY NOT BECOME APPARENT UNTIL DAYS TO WEEKS AFTER A FIRE • Unconsciousness or obtunded • Recumbency and inability or reluctance to walk • Extensive burns covering 10–15% of the body or vital areas such as the feet • Substantial limb or facial swelling • Respiratory signs such as dyspnoea, coughing or frothing at the nose or mouth • Hoof damage that has led or is likely to lead to separation of the hooves from the coronary band

Box 2.2  NON-CLINICAL FACTORS THAT MAY INFLUENCE A DECISION TO HUMANELY KILL BUSHFIRE-AFFECTED SHEEP.106,107,108 • Whether there are facilities available for treating and nursing affected sheep, including for confinement, restraint, and shelter • Whether adequate feed and water are available for remaining animals • The willingness and ability of clients to care for affected sheep—psychologically, financially, practically • The ability of the veterinarian to revisit the property for ongoing monitoring, treatment and assessment of sheep • How any illness, confinement, treatment, isolation from herd mates or close contact with humans might impact the mental and emotional state of the patient • Other options available for apparently unaffected sheep, such as salvage slaughter • The value of the sheep to the client (genetic, financial, emotional)

Although hospitalisation and intensive treatment are possible for sheep, these are not usually undertaken due to practical or financial reasons. Even with intensive treatment, there is some limited evidence that outcomes may still be poor. Chigerwe et al. (2020)109 reported that, of 12 sheep admitted to a US veterinary teaching hospital with full-thickness burns involving the dermis and epidermis after wildfires, 11 were euthanised and one died due to septicaemia. Production losses may occur in flocks close to fire affected areas. US producers have reported in a survey that, following wildfires, sheep had reduced conceptions,

34

CHAPTER 2: Welfare of Sheep

weight gain, birthweight and milk production, as well as higher abortion rates.110 Pneumonia, likely from smoke inhalation, was also reported.110 Proximity and exposure to smoke and flames may in themselves also act as a psychological stressor for sheep. In summary, veterinary decision making about bushfire-affected sheep should consider: the health and welfare of sheep now and during any proposed treatment; the capability of veterinarians and clients to provide ongoing monitoring and treatment; the resources available for treating, nursing and managing sheep; the availability of options such as salvage slaughter; and the wellbeing of clients.

2.9  WELFARE MONITORING AND RECORD KEEPING Monitoring of health and welfare indicators and the keeping of good flock records can provide a tool that producers and veterinarians can use to improve sheep welfare. Records of health and welfare indicators can help to identify target areas for improvement and to set a standard for incremental progress year on year. Indicators of animal welfare can be resource-based (such as quality and quantity of food provided, stocking density, whether or not shelter is provided) or animal-based (such as behavioural indicators, body condition score, presence or absence of flystrike). While resource-based measures are often easier to measure, animal-based measures are considered a more direct way of measuring animal welfare and are thus preferable. Some animal-based indicators of sheep welfare that can be measured in a representative sample of the flock and monitored regularly over time include body condition score, lameness, fleece condition, skin lesions and dag score.111 Mortality of both adult and juvenile sheep should also be recorded, and trends monitored over time. Producers have been shown to be more likely to perform health monitoring such as body condition scoring and faecal egg counts if they feel that these activities are important/valuable.112 This highlights an opportunity for veterinarians to communicate the importance and value of sheep health and welfare monitoring to producers.

2.10 CONCLUSIONS Working to improve and safeguard animal welfare is a core part of a veterinarian’s role. Although a naturally hardy animal, farmed sheep require careful monitoring and care to avoid welfare problems though disease conditions and malnutrition. In addition, sheep have traditionally been

subjected to a range of tissue-altering surgical husbandry procedures that in themselves can be painful unless ameliorated through anaesthesia, analgesia and the adoption of lower-impact methods. Although some of these surgical husbandry procedures can justifiably be claimed to prevent even worse welfare problems from occurring, increased public scrutiny of farming practices and consumer expectations for the provenance and animal welfare credentials of sheep products both mean that continuous improvement of sheep welfare will be necessary for industry sustainability.

REFERENCES 1. World Organisation for Animal Health (2023) Animal welfare. https://www.woah.org/en/ what-we-do/animal-health-and-welfare/animalwelfare/#:~:text=According%20to%20the%20 Terrestrial%20Code,socio%2Deconomic%20and%20 ecological%20systems. 2. Fraser D, Weary DM, Pajor EA et al. (1997) A scientific conception of animal welfare that reflects ethical concerns. Anim Welf 6 187–205. https://doi.org/10.1017/ S0962728600019795. 3. Lauber M, Nash JA, Gatt A et al. (2012) Prevalence and incidence of abnormal behaviours in individually housed sheep. Animals 2 27–37. https://doi.org/10.3390/ ani2010027. 4. Browning H (2020) The natural behavior debate: Two conceptions of animal welfare. J Appl Anim Welf Sci 23 325–37. https://doi.org/10.1080/10888705.2019.1672552. 5. Mellor DJ, Beausoleil NJ, Littlewood KE et al. (2020) The 2020 five domains model: Including human-animal interactions in assessments of animal welfare. Animals 10. https://doi.org/10.3390/ani10101870. 6. Mellor DJ (2012) Animal emotions, behaviour and the promotion of positive welfare states. NZ Vet J 60 1–8. https://doi.org/10.1080/00480169.2011.619047. 7. Mellor DJ (2019) Welfare-aligned sentience: Enhanced capacities to experience, interact, anticipate, choose and survive. Animals 9. https://doi.org/10.3390/ani9070440. 8. Dawkins MS (2020) The science of animal welfare: Understanding what animals want. Oxford University Press: Oxford. https://doi.org/10.1093/ oso/9780198848981.001.0001. 9. Dwyer C (2017) The behaviour of sheep and goats. In: The ethology of domestic animals: An introductory text, ed P Jensen. 3rd ed. CABI: Oxfordshire, pp. 199–213. https://doi. org/10.1079/9781786391650.019. 10. Hinch GN (2017) Understanding the natural behaviour of sheep. In: Advances in sheep welfare, eds DM Ferguson, C Lee and A Fisher. Elsevier: Cambridge, pp. 3–17. https:// doi.org/10.1016/B978-0-08-100718-1.00001-7. 11. Dwyer CM (2021) Behavioral biology of sheep. In: Behavioural biology of laboratory animals, eds K Coleman and

R e f e r e nc e s

SJ Schapiro. 1st ed. CRC Press: Boca Raton, pp. 261–71. https://doi.org/10.1201/9780429019517. 12. Häger C, Biernot S, Buettner M et al. (2017) The sheep grimace scale as an indicator of post-operative distress and pain in laboratory sheep. PLOS One 12. https://doi. org/10.1371/journal.pone.0175839. 13. McLennan KM, Rebelo CJB, Corke MJ et al. (2016) Development of a facial expression scale using footrot and mastitis as models of pain in sheep. Appl Anim Behav Sci 176 19–26. https://doi.org/10.1016/j. applanim.2016.01.007. 14. Guesgen MJ, Beausoleil NJ, Leach M et al. (2016) Coding and quantification of a facial expression for pain in lambs. Behav Processes 132 49–56. https://doi.org/10.1016/j. beproc.2016.09.010. 15. Doyle RE (2017) Sheep cognition and its implications for welfare. In: Advances in sheep welfare, eds DM Ferguson, C Lee and A Fisher. Elsevier: Cambridge, pp. 55–71. https:// doi.org/10.1016/B978-0-08-100718-1.00004-2. 16. Mendl M (1999) Performing under pressure: Stress and cognitive function. Appl Anim Behav Sci 65 221–44. https://doi.org/10.1016/S0168-1591(99)00088-X. 17. Mendl M, Nicol CJ (2017) Learning and cognition. In: The ethology of domestic animals: An introductory text, ed P Jensen. 3rd ed. CABI: Oxfordshire, pp. 62–78. https://doi. org/10.1079/9781786391650.00. 18. Kendrick KM, da Costa AP, Leigh AE et al. (2002) Sheep don’t forget a face. Nature 414 165–6. https://doi. org/10.1038/35102669. 19. Clarke PG, Whitteridge D. (1973) The basis of stereoscopic vision in the sheep. J Physiol 229 22P–3P. https://doi.org/10.1113/jphysiol.1973.sp19732 291toc. 20. Hutson GD (1985) The influence of barley food rewards on sheep movement through a handling system. Appl Anim Behav Sci 14 263–73. https://doi.org/10.1016/01681591(85)90007-3. 21. Hutson GD (1981) An evaluation of some traditional and contemporary views on sheep behaviour. Wool Tech Sheep Breed 29 3–6. 22. Franklin JR and Hutson GD (1982) Experiments on attracting sheep to move along a laneway. III: Visual stimuli. Appl Anim Ethol 8 457–78. https://doi. org/10.1016/0304-3762(82)90059-1. 23. Bremner KJ (1980) Training sheep as leaders in abattoirs and farm sheep yards. Proc NZ Soc Anim Prod 40 111–16. 24. Hargreaves AL and Hutson GD (1997) Handling systems for sheep. Livest Prod Sci 49 121–38. https://doi. org/10.1016/S0301-6226(97)00009-2. 25. Barber AA and Freeman RB (1986) Design of shearing sheds and sheep yards. Inkata Press: Melbourne. 26. Rushen J and Congdon P (1986) Relative aversion of sheep to simulated shearing with and without electroimmobilisation. Aust J Exp Agric 26 535–7. https://doi. org/10.1071/EA9860535.

35

27. Animal Health Australia (AHA) (2014) Australian animal welfare standards and guidelines—sheep. https://www. integritysystems.com.au/globalassets/isc/pdf-files/sheepstandards-and-guidelines-for-endorsed-jan-2016-061017.pdf. 28. Jorgenson JT, Festa-Bianchet M, Gaillard J-M et al. (1997) Effects of age, sex, disease, and density on survival of Bighorn sheep. Ecology 78 1019–32. https://doi. org/10.1890/0012-9658(1997)078[1019:EOASDA]2.0.CO. 29. Clutton-Brock TH, Price OF, Albon SD et al. (1992) Early development and population fluctuations in Soay sheep. J Anim Ecol 61 381–96. https://doi.org/10.2307/5330. 30. Hansen BG and Østerås O (2019) Farmer welfare and animal welfare—exploring the relationship between farmer’s occupational well-being and stress, farm expansion and animal welfare. Prev Vet Med 170 104741. https://doi. org/10.1016/j.prevetmed.2019.104741. 31. Stafford K (2017) Husbandry procedures. In: Advances in sheep welfare, eds DM Ferguson, C Lee and A Fisher. Elsevier: Cambridge, pp. 211–26. https://doi.org/10.1016/ B978-0-08-100718-1.00011-X. 32. Sutherland MA and Tucker CB (2011) The long and short of it: A review of tail docking in farm animals. Appl Anim Behav Sci 135 179–91. https://doi.org/10.1016/j. applanim.2011.10.015. 33. Orihuela A and Ungerfeld R. (2019) Tail docking in sheep (Ovis aries): A review on the arguments for and against the procedure, advantages/disadvantages, methods, and new evidence to revisit the topic. Livest Sci 230. https://doi. org/10.1016/j.livsci.2019.103837. 34. Gascoigne E, Mouland C and Lovatt F (2021) Considering the 3Rs for castration and tail docking in sheep. In Pract 43 152–62. https://doi.org/10.1002/inpr.29. 35. Webb Ware J, Vizard A and Lean G (2000) Effects of tail amputation and treatment with an albendazole controlled-release capsule on the health and productivity of prime lambs. Aust Vet J 78 838–42. https://doi. org/10.1111/j.1751-0813.2000.tb10504.x. 36. Howard K and Beattie L (2018) A national producer survey of sheep husbandry practices. Meat and Livestock Australia Report. https://www.mla.com.au/contentassets/c6b8854d 3bb6421aab1a94baf9496b9a/e.aww.1501_final_report_-_ sheep.pdf. Accessed 29 March 2023. 37. Mellor DJ and Stafford KJ (2000) Acute castration and/ or tailing distress and its alleviation in lambs. N Z Vet J 48 33–43. https://doi.org/10.1080/00480169.2000.36156. 38. Lomax S, Dickson H, Sheil M et al (2010) Topical anaesthesia alleviates short-term pain of castration and tail docking in lambs. Aust Vet J 88 67–74. https://doi. org/10.1111/j.1751-0813.2009.00546.x. 39. Grant C (2004) Behavioural responses of lambs to common painful husbandry procedures. Appl Anim Behav Sci 87 255–73. https://doi.org/10.1016/j.applanim.2004.01.011. 40. Small A, Fisher AD, Lee C et al. (2021) Analgesia for sheep in commercial production: Where to next? Animals 11. https://doi.org/10.3390/ani11041127.

36

CHAPTER 2: Welfare of Sheep

41. Anonymous (2022) Sheep sustainability framework-on-farm insights from the national producer survey. https://www. sheepsustainabilityframework.com.au/globalassets/sheepsustainability/media/ssf-on-farm-insights-report-web25oct2022.pdf. Accessed 29 March 2023. 42. Small A, Fetiveau M, Smith R et al. (2021) Three studies evaluating the potential for lidocaine, bupivacaine or procaine to reduce pain-related behaviors following ring castration and/or tail docking in lambs. Animals 11. https:// doi.org/10.3390/ani11123583. 43. Australian Veterinary Association (2022) Proposed amendment to the poisons standard-3.4 lidocaine submission of the Australian veterinary association. https://www.ava.com.au/ siteassets/advocacy/ava-submission-lidocaine-reschedulingfinal-20-1-22.pdf. Accessed 29 March 2023. 44. Woodruff ME, Doyle R, Coleman G et al. (2020) Knowledge and attitudes are important factors in farmers’ choice of lamb tail docking length. Vet Rec 186 1–9. https://doi.org/10.1136/vr.105631. 45. Johnston CH, Richardson VL and Whittaker AL (2023) How well does Australian animal welfare policy reflect scientific evidence: A case study approach based on lamb marking. Animals 13 1358. https://doi.org/10.3390/ ani13081358. 46. Sinnett A, Dunshea F, D’Souza D et al. (2021) A desktop cost benefit analysis of pork production with entire male vs immunocastration. Australian Pork Limited. https:// australianpork.com.au/sites/default/files/2021-11/Final%20 Report_2020_0075.pdf. 47. Lomax S, Dickson H, Sheil M et al. (2010) Topical anaesthesia alleviates short-term pain of castration and tail docking in lambs. Aust Vet J 88 67–74. https://doi. org/10.1111/j.1751-0813.2009.00546.x. 48. Melches S, Mellema SC, Doherr MG et al. (2007) Castration of lambs: A welfare comparison of different castration techniques in lambs over 10 weeks of age. Vet J 173 554–63. https://doi.org/10.1016/j.tvjl.2006.01.006. 49. Lester SJ, Mellor DJ, Holmes RJ et al. (1996) Behavioural and cortisol responses of lambs to castration and tailing using different methods. NZ Vet J 44 45–54. https://doi. org/10.1080/00480169.1996.35933. 50. Small AH, Belson S, Holm M et al. (2014) Efficacy of a buccal meloxicam formulation for pain relief in Merino lambs undergoing knife castration and tail docking in a randomised field trial. Aust Vet J 92 381–8. https://doi. org/10.1111/avj.12241. 51. Small AH, Jongman EC, Niemeyer D et al. (2020) Efficacy of precisely injected single local bolus of lignocaine for alleviation of behavioural responses to pain during tail docking and castration of lambs with rubber rings. Res Vet Sci 133 210–18. https://doi.org/10.1016/j. rvsc.2020.09.025. 52. Lee C, Fisher AD (2007) Welfare consequences of mulesing of sheep. Aust Vet J 85 89–93. https://doi. org/10.1111/j.1751-0813.2007.00114.x.

53. Fisher AD, Giraudo A, Martin PAJ et al. (2013) The use of quantitative risk assessment to assess lifetime welfare outcomes for breech strike and mulesing management options in Merino sheep. Animal Welfare 22 267–75. https://doi.org/10.7120/09627286.22.2.267. 54. Colvin AF, Reeve I, Kahn LP et al. (2022) Australian surveys on incidence and control of blowfly strike in sheep between 2003 and 2019 reveal increased use of breeding for resistance, treatment with preventative chemicals and pain relief around mulesing. Vet Parasitol Reg Stud Reports 31 100725. https://doi.org/10.1016/j.vprsr.2022.100725. 55. Peachey B (2019) Rate of genetic gain in reducing breech flystrike-update. https://www.wool.com/globalassets/wool/ sheep/research-publications/welfare/flystrike-researchupdate/project-report-rate-of-genetic-gain-in-reducingbreech-flystrike-update-june-2019.pdf. Accessed 29 March 2023. 56. Brien FD, Walkom SF, Swan AA et al. (2020) Substantial genetic gains in reducing breech flystrike and in improving productivity traits are achievable in Merino sheep by using index selection. Anim Prod Sci 61 345–62. https://doi. org/10.1071/AN20248. 57. Vilanova XM, De Briyne N, Beaver B et al. (2019) Horse welfare during equine chorionic gonadotropin (eCG) production. Animals 9 https://doi.org/10.3390/ani9121053. 58. Candappa IBR and Bartlewski PM (2011) A review of advances in artificial insemination (AI) and embryo transfer (ET) in sheep, with the special reference to hormonal induction of cervical dilation and its implications for controlled animal reproduction and surgical techniques. Open Repro Sci J 3 162–75. https://doi.org/10.2174/18742 55601103010162. 59. Dwyer C (2017) Reproductive management (including impacts of prenatal stress on offspring development). In: Advances in sheep welfare, eds DM Ferguson, C Lee and A Fisher. Elsevier: Cambridge, pp. 131–52. https://doi. org/10.1016/B978-0-08-100718-1.00007-8. 60. Stafford K, Chambers J, Sylvester S et al. (2006) Stress caused by laparoscopy in sheep and its alleviation. NZ Vet J 54 109–13. https://doi.org/10.1080/00480169.2006.36621. 61. Rushen J (1986) Aversion of sheep for handling treatments: Paired-choice studies. Appl Anim Behav Sci 16 363–70. https://doi.org/10.1016/0168-1591(86)90008-0. 62. European Society of Veterinary Clinical Ethology. ESVCE position statement on the use of medications to manage acute phobic states in dogs as an alternative to acepromazine. https:// esvce.org/wp-content/uploads/2022/07/ESVCE-PositionStatement-Use-of-Acepromazone.pdf. Accessed 26 March 2023. 63. Oliveira FC, Haas CS, Ferreira CER et al (2018) Inflammatory markers in ewes submitted to surgical or transcervical embryo collection. Small Rumin Res 158 15–18. https://doi.org/10.1016/j.smallrumres.2017.11.012. 64. Santos JDR, Ungerfeld R, Balaro MFA et al. (2020) Transcervical vs. laparotomy embryo collection in ewes:

R e f e r e nc e s

The effectiveness and welfare implications of each technique. Theriogenology 153 112–21. https://doi. org/10.1016/j.theriogenology.2020.05.004. 65. Fonseca JF, Souza-Fabjan JMG, Oliveira MEF et al. (2016) Nonsurgical embryo recovery and transfer in sheep and goats. Theriogenology 86 144–51. https://doi. org/10.1016/j.theriogenology.2016.04.025. 66. DeRossi R, Carneiro RPB, Ossuna MR et al. (2009) Sub-arachnoid ketamine administration combined with or without misoprostol/oxytocin to facilitate cervical dilation in ewes: A case study. Small Rumin Res 83 74–8. https://doi. org/10.1016/j.smallrumres.2009.03.002. 67. Damián JP and Ungerfeld R (2011) The stress response of frequently electroejaculated rams to electroejaculation: Hormonal, physiological, biochemical, haematological and behavioural parameters. Reprod Domest Anim 46 646–50. https://doi.org/10.1111/j.14390531.2010.01722.x. 68. Abril-Sánchez S, Freitas-de-Melo A, Giriboni J et al. (2019) Sperm collection by electroejaculation in small ruminants: A review on welfare problems and alternative techniques. Anim Reprod Sci 205 1–9. https://doi.org/10.1016/j. anireprosci.2019.03.023. 69. Abril-Sánchez S, Freitas-de-Melo A, Damián JP et al. (2017) Ejaculation does not contribute to the stress response to electroejaculation in sheep. Reprod Domest Anim 52 403–8. https://doi.org/10.1111/rda. 12922. 70. LiveCorp and Meat and Livestock Australia. Heat stress. In: Veterinary handbook. http://www.veterinaryhandbook. com.au/Diseases.aspx?diseasenameid=116&id=46. Accessed 12 March 2023. 71. Lees AM, Lees JC, Sejian V et al. (2017) Management strategies to reduce heat stress in sheep. In: Sheep production adapting to climate change, eds V Seijan, R Bhatta, J Gaughan et al. Springer: Singapore, pp. 349–70. https://doi. org/10.1007/978-981-10-4714-5_17. 72. Marai IFM, El-Darawany AA, Fadiel A et al. (2007) Physiological traits as affected by heat stress in sheep—a review. Small Rumin Res 71 1–12. https://doi. org/10.1016/j.smallrumres.2006.10.003. 73. Sula MJM, Winslow CM, Boileau MJ et al. (2012) Heatrelated injury in lambs. J Vet Diagn Invest 24 772–6. https://doi.org/10.1177/10406387124457. 74. van Wettere WHEJ, Kind KL, Gatford KL et al. (2021) Review of the impact of heat stress on reproductive performance of sheep. J Anim Sci Biotechnol 12. https:// doi.org/10.1186/s40104-020-00537-z. 75. Holm Glass M and Jacob R (1991) Losses of sheep following adverse weather after shearing. Aust Vet J 69 142–3. https://doi.org/10.1111/j.1751-0813.1992. tb07486.x. 76. Hinch GN and Brien F (2014) Lamb survival in Australian flocks: A review. Anim Prod Sci 54 656–66. https://doi. org/10.1071/AN13236.

37

77. Ley SJ, Livingston A and Waterman AE (1989) The effect of chronic clinical pain on thermal and mechanical thresholds in sheep. Pain 39 353–7. https://doi. org/10.1016/0304-3959(89)90049-3. 78. Carter GR and Henderson JA (1955) Contagious foot rot in sheep. Can J Comp Med Vet Sci 19 26–9. 79. McLennan KM, Rebelo CJB, Corke MJ et al. (2016) Development of a facial expression scale using footrot and mastitis as models of pain in sheep. Appl Anim Behav Sci 176 19–26. https://doi.org/10.1016/j. applanim.2016.01.007. 80. Fitzpatrick J, Scott M and Nolan A (2006) Assessment of pain and welfare in sheep. Small Ruminant Res 62 55–61. https://doi.org/10.1016/j.smallrumres.2005.07.028. 81. Dolan S, Field LC and Nolan AM (2000) The role of nitric oxide and prostaglandin signaling pathways in spinal nociceptive processing in chronic inflammation. Pain 86 311–20. https://doi.org/10.1016/S0304-3959(00)00262-1. 82. Clune T, Lockwood A, Hancock S et al. (2022) Abortion and lamb mortality between pregnancy scanning and lamb marking for maiden ewes in Southern Australia. Animals 12 10. https://doi.org/10.3390/ani12010010. 83. Dwyer CM, Conington J, Corbiere F et al. (2016) Invited review: Improving neonatal survival in small ruminants: Science into practice. Animal 10 449–59. https://doi. org/10.1017/S1751731115001974. 84. Hinch GN and Brien F. (2014) Lamb survival in Australian flocks: A review. Anim Prod Sci 54 656–66. https://doi. org/10.1071/AN13236. 85. Kopp K, Hernandez-Jover M, Robertson S et al. (2020) A survey of New South Wales sheep producer practices and perceptions on lamb mortality and ewe supplementation. Animals 10 1586. https://doi.org/10.3390/ani10091586. 86. Dwyer CM (2008) The welfare of the neonatal lamb. Small Ruminant Res 76 31–41. https://doi.org/10.1016/j. smallrumres.2007.12.011. 87. Refshauge G, Brien FD, Hinch GN et al. (2016) Neonatal lamb mortality: Factors associated with the death of Australian lambs. Anim Prod Sci 56 726–35. https://doi. org/10.1071/AN15121. 88. Mellor DJ and Stafford KJ (2004) Animal welfare implications of neonatal mortality and morbidity in farm animals. Vet J 168 118–33. https://doi.org/10.1016/j. tvjl.2003.08.004. 89. Mellor DJ and Diesch TJ (2006) Onset of sentience: The potential for suffering in fetal and newborn farm animals. Appl Anim Behav Sci 100 48–57. https://doi.org/10.1016/j. applanim.2006.04.012. 90. Broadmeadow M, O’Sullivan BM, Gibson JE et al. (1984) The pathogenesis of flystrike in sheep. Wool Tech Sheep Breeding 32 28–32. 91. Sackett D, Holmes P, Abbott K et al. (2006) Project AHW. 087 report to MLA: Assessing the economic cost of endemic disease on the profitability of Australian beef cattle and sheep producers. Meat and Livestock Australia Ltd: North Sydney.

38

CHAPTER 2: Welfare of Sheep

92. Horton BJ, Corkrey R and Doughty AK (2018) Sheep death and loss of production associated with flystrike in mature Merino and crossbred ewes. Anim Prod Sci 58 1289–96. https://doi.org/10.1071/AN16153. 93. Colditz IG, Walkden-Brown SW, Daly BL et al. (2005) Some physiological responses associated with reduced wool growth during blowfly strike in Merino sheep. Aust Vet J 83 695–9. https://doi.org/10.1111/j.1751-0813.2005. tb13053.x. 94. Still Brooks KM (2019) Field euthanasia techniques for small ruminants. American Association of Bovine Practitioners Conference Proceedings, St. Louis, MI, 12–14 September, pp. 187–91. https://doi.org/10.21423/aabppro20197134. 95. Humane Slaughter Association (2022) On-farm humane killing of neonate pigs, goats and sheep. https://www.hsa.org. uk/downloads/on-farm-killing-of-neonates-march-2022. pdf. Accessed 30 March 2023. 96. American Veterinary Medical Association (2020) AVMA guidelines for the euthanasia of animals: 2020 edition. https:// www.avma.org/resources-tools/avma-policies/avmaguidelines-euthanasia-animals. Accessed 30 March 2023. 97. American Veterinary Medical Association (2016) AVMA guidelines for the humane slaughter: 2016 edition. https://www. avma.org/resources-tools/avma-policies/avma-guidelineseuthanasia-animals. Accessed 30 March 2023. 98. Grist A, Lines JA, Knowles TG et al. (2018) The use of a mechanical non-penetrating captive bolt device for the euthanasia of neonate lambs. Animals 8 49. https://doi. org/10.3390/ani8040049. 99. World Organisation for Animal Health (2016) Slaughter of animals. In: Terrestrial animal health code. https://www. woah.org/en/what-we-do/standards/codes-and-manuals/ terrestrial-code-online-access/?id=169&L=1&htmfile=chap itre_aw_slaughter.htm. Accessed 11 March 2023. 100. Stanger KJ, Kells NJ, Fisher AD et al. (2019) Evaluation of euthanasia of sheep with intravenous saturated salt solutions to enable the collection of whole, intact brains. Anim Welf 28 397–406. https://doi. org/10.7120/09627286.28.4.397. 101. Jubb T (2013) How to use a penetrating captive bolt gun. Aust Cattle Vet 26–30. https://www.ava.com.au/libraryresources/library/ava-scientific-journals/acv/2013/howto-use-a-penetrating-captive-bolt-gun/Issue%2067%20 Jubb.pdf. 102. LiveCorp and Meat and Livestock Australia. Confirming death. In: Veterinary handbook. http://www.

veterinaryhandbook.com.au/ContentSection.aspx?id=39. Accessed 11 March 2023. 103. Finnie JW, Manavis J, Blumbergs PC et al. (2002) Brain damage in sheep from penetrating captive bolt stunning. Aust Vet J 80 67–69. https://doi. org/10.1111/j.1751-0813.2002.tb12053.x. 104. HAS (2023) The humane slaughter association. https://www. hsa.org.uk/. Accessed 13 March 2023. 105. Grandin T. Livestock behaviour, design of facilities and humane slaughter. https://www.grandin.com/. Accessed 13 March 2023. 106. Cowled BD, Bannister-Tyrrell M, Doyle M et al (2022) The Australian 2019/2020 Black Summer bushfires: Analysis of the pathology, treatment strategies and decision making about burnt livestock. Front Vet Sci 9. https://doi. org/10.3389/fvets.2022.790556. 107. Department of Primary Industries, New South Wales Government (2018) Assessing bush fire burns in livestock. PrimeFact 399. 4th ed. https://www.dpi.nsw.gov.au/__data/ assets/pdf_file/0007/96811/Assessing-bushfire-burns-inlivestock.pdf. 108. Agriculture Victoria, Victorian Government (2021) Assessing sheep after a bushfire. https://agriculture.vic.gov. au/farm-management/emergency-management/bushfires/ what-to-do-after-a-bushfire/assessing-sheep-after-abushfire#:~:text=Sheep%20must%20be%20inspected%20 daily,return%20after%20about%20a%20week. Accessed 13 March 2023. 109. Chigerwe M, Depenbrock SM, Heller MC et al. (2020) Clinical management and outcomes for goats, sheep, and pigs hospitalized for treatment of burn injuries sustained in wildfires: 28 cases (2006, 2015, and 2018). J Am Vet Med Assoc 257 1165–70. https://doi.org/10.2460/ javma.2020.257.11.1165. 110. O’Hara KC, Ranches J, Roche LM et al. (2021) Impacts from wildfires on livestock health and production: Producer perspectives. Animals 11. https://doi.org/10.3390/ ani11113230. 111. Munoz C, Campbell A, Hemsworth P et al. (2018) Animalbased measures to assess the welfare of extensively managed ewes. Animals 8. https://doi.org/10.3390/ani8010002. 112. Munoz CA, Coleman GJ, Hemsworth PH et al. (2019) Positive attitudes, positive outcomes: The relationship between farmer attitudes, management behaviour and sheep welfare. PLOS One 14. https://doi.org/10.1371/ journal.pone.0220455.

chapter 3

ENERGY AND PROTEIN NUTRITION OF GRAZING SHEEP

39

Philip Hynd

3.1 INTRODUCTION Australia has the largest grazing land area in the world (4.4  million km2), followed by China (2.4  million km2), Brazil (1.7 million km2) and Argentina (1.4 million km2).1 Grazed pastures are the cheapest source of nutrients for ruminants. By making some assumptions about land costs, pasture establishment and maintenance costs and digestible dry matter production, the cost of pasture can be estimated at approximately $0.12/kg dry matter (DM) consumed ($120/tonne DM) or $0.011/MJ of metabolisable energy,2 in comparison to grain, for example, at $350–400/ tonne DM or $0.03–0.04/MJ. Feed represents the highest cost of production in animal enterprises, so grazing pastures and crop residues will continue to play an important role in sheep production systems, and increasingly so as competition for human-digestible feeds increases. Sheep in mixed cropping/sheep enterprises also play an important role in the utilisation of poor-quality, low-nutritivevalue crop residues; recycling of nutrients; management of weeds; diversification of income; and management of risk for producers. Despite their benefits, the quantity and quality of pastures is highly seasonal and often poorly aligned with the nutritional requirements of the sheep grazing them. In Mediterranean environments, plant growth is limited in summer by low rainfall and in winter by low temperatures, leaving a period in spring of rapid pasture growth. The quality (metabolisable energy, protein and mineral content) of the pasture plants also varies throughout the year. Together, these factors mean that sheep are faced with effectively four pasture scenarios: spring (high quality, high quantity), summer (low quality, high quantity), autumn (low quality, low quantity) and winter (high quality, low quantity). In cold-temperate climates (for example, the tablelands of NSW) similar variations occur but with a strong influence of cold temperatures on plant growth. Poor matching of the nutrients available to the demands of grazing sheep is a major contributor to poor productivity and profitability for some grazing enterprises. In this chapter the systems of measuring and defining the energy and protein nutritional needs of sheep are first described,

followed by a summary of the ways in which the nutritional requirements can be met in pasture-based systems.

3.2  ENERGY AND PROTEIN REQUIREMENTS OF GRAZING SHEEP 3.2.1  Ruminant Digestion In an evolutionary sense, ruminants have been among the most successful groups of mammals in the world, largely as a consequence of a symbiotic relationship between the host animal and its resident anaerobic microbes. The host provides an environment conducive to anaerobic fermentation (that is, an environment which is anaerobic, pH-buffered, isotonic, temperature-controlled and from which waste products are removed continuously, and with a wide diversity of microenvironments). The microbes, in turn, digest feed, producing volatile fatty acids (VFAs) as end-products that the host uses as an energy source, a supply of microbial protein of moderate quality, a supply of microbial lipids and a supply of the vitamins B and K. The VFAs are mainly acetic (C2), propionic (C3) and butyric (C4) acids with small amounts of longer-chain acids such as iso-butyric (C4), valeric (C5) and iso-valeric (C5) acids. These acids are the end-products of the fermentation of simple sugars and complex carbohydrates like cellulose, hemicellulose and starches by bacteria, fungi and ciliated protozoans. The type of microbes present (for example, cellulolytic, amylolytic, proteolytic, lactate-utilisers, methanogens) and the relative proportions of the VFAs produced are determined by the composition of the diet consumed and the prevailing physico-chemical environment. The fermentation acids are absorbed across the ruminal epithelium by two main mechanisms—direct exchange of dissociated acids with bicarbonate ions (about 50%) and passive absorption of undissociated VFA (about 40%). Both mechanisms tend to buffer the ruminal fluid from large pH drops because the undissociated acids take their hydrogen ion with them out of the fluid (increasing pH) and the dissociated ions are swapped with a bicarbonate buffering ion.3 Butyrate is converted to β-OH butyrate (beta-hydroxy butyrate, a ketone body) on passage through the ruminal epithelium, but the acetate and propionate are unchanged. All three

DOI: 10.1201/9781003344346-3

40

CHAPTER 3: Energy and Protein Nutrition of Grazing Sheep

Figure 3.1  Carbohydrates like cellulose, starches and sugars are fermented to simple volatile fatty acids, creating energy-rich ATP which drives the synthesis of microbial protein from simple nitrogen compounds like ammonia. The simpler the carbohydrates, the faster the gear spins and the more rapid the microbial protein synthesis. Source: Philip Hynd.

nitrogen accounts for the remarkable success of ruminant animals in a wide range of environments around the world. We can take advantage of this utilisation of non-protein nitrogen to form proteins by maintaining sheep on lownitrogen diets or very low-quality diets supplemented with urea or other inexpensive non-protein sources. The resulting microbial protein then joins with dietary proteins that are not degraded in the rumen. Carbohydrates differ widely in the rate at which they are fermented. Simple sugars and starches are the most rapidly fermented, followed by hemicelluloses, pectins and, finally, celluloses, which are slowly fermented. The rate of fermentation is important because it largely dictates the amount of feed the sheep can consume; voluntary intake by ruminants is directly related to the rate at which the feed material is

Figure 3.2  Partitioning of feed energy in sheep. Typical energy values in megajoules/kg of dry matter are shown to the left of the diagram. Note that the main determinant of energy available to the animal is the digestibility of the feed. Source: Philip Hynd.

acids travel to the liver through the portal vein and enter the biochemical pathways that generate energy, glucose, ketone bodies, lipids and proteins. In the process of fermenting the dietary carbohydrates, the microbes obtain ATP,a which they can then use for metabolic processes, including the synthesis of proteins essential to life. These proteins are largely synthesised from simple nitrogenous compounds like ammonia and small peptides (Figure 3.1). This unique ability of anaerobic microbes to produce protein from non-protein  ATP—adenosine triphosphate, the source of energy to power many cellular processes in animals.

a

digested in, or leaves, the rumen. High-fibre diets containing a large amount of slowly digested cellulose are slowly degraded, so the feed particles remain in the rumen for many days, contributing to rumen ‘fill’ and thereby restricting intake. High-fibre diets are also digested to a lower extent than lower-fibre diets. Dietary energy is measured in megajoules (MJ), and digestibility is the main determinant of the energy density of the diet (Figure 3.2). The digestibility of a feed therefore determines the two most important components of energy available to the sheep: its energy density and how much of it the sheep can consume. Together these determine the total intake of available energy. The digestibility of a feed depends on the

3. 2 E n e rg y a n d P ro t e i n R e qu i r e m e n t s of G r a z i ng Sh e e p

content of indigestible (lignin, silica) and poorly digestible (cellulose) components, but other factors, including its nitrogen content, mineral content, particle size and structural features, can also play a role. Any factor that limits microbial activity will reduce digestibility, intake and performance. The microbial protein produced during fermentation joins with dietary protein that is not degraded in the rumen and becomes available to the host as amino acids after digestion in the abomasum and small intestines. The diagram in Figure 3.3 summarises the digestive processes taking place in the reticulorumen and the supply of nutrients available to the sheep for metabolism and production. The major absorbed nutrients are VFAs (acetate, propionate), the ketone body β-OH butyrate, amino acids, long-chain saturated fatty acids, simple sugars, minerals and vitamins. Importantly, of these, only certain amino acids (gluconeogenic amino acids) and propionate are able to produce the glucose that is essential for brain function and foetal growth. This becomes important when pregnant ewes, and particularly those bearing multiple lambs, suffer an energy deficit in the last month of pregnancy, resulting in pregnancy toxaemia. The relative proportions of the VFAs change with the diet. Roughage diets and poor-quality, senesced pastures and crop residues initiate fermentations characterised by relatively high acetate levels. High-grain rations and lush, green

41

pastures produce relatively high levels of propionate. High-sugar diets produce relatively high levels of butyrate. Figure 3.4 shows the impact of the ratio of concentrate to roughage on relative VFA proportions and the minimum pH likely to be generated. The rumen pH is directly and inversely related to the total concentration of VFA.

3.2.2  Estimating the Energy Requirements of Grazing Sheep It is clear from Figures 3.2 and 3.3 that the most important form of energy available to the sheep for maintenance and production is called the net energy (NE), which is the energy remaining after fermentation, digestion, absorption and metabolism. Net energy, however, is difficult to measure because it requires feeding the animal and collecting all faeces, urine, gas outputs and heat production for each feed available. Given the infinite variety of forages available to a sheep throughout the year, and even throughout the day, it would be impossible to do this. Instead, we use a metabolisable energy (ME) system in which the ME content of the feed is estimated from average tabulated values for digestibility, methane output and urine energy output. The efficiency of conversion of ME to NE is then estimated using efficiency factors, called k factors, which are calculated from the feed quality and the purpose for which the energy is being used (for example, lactation, maintenance, gestation, activity, growth). The total ME required

Figure 3.3  The flows of nitrogenous compounds and energy-rich substances between the feed source, rumen, abomasum and intestinal tract and the liver of the ruminant. Source: Philip Hynd.

42

CHAPTER 3: Energy and Protein Nutrition of Grazing Sheep

Figure 3.4  Effect of the ratio of concentrate to roughage on the relative proportions of volatile fatty acids (VFAs) and minimal ruminal pH. Source: Philip Hynd.

by the sheep can then be calculated by adding up all of the ME requirements for each purpose as follows: ME requirement ( MJ / day ) = ME m + ME l + ME p + ME g + ME a + ME c

(1)

where MEm = ME for maintenance MEl = ME for milk production MEp = ME for pregnancy MEg = ME for growth MEa = ME for activity (walking, grazing, ruminating, standing) MEc = ME required to maintain core body temperature This chapter now considers these in detail, along with the consequences of not providing sufficient ME for each purpose.

3.2.3  Maintenance Energy Requirement of Penned Sheep The energy required to support the basic life-sustaining processes of a sheep (cellular metabolism, osmoregulation, respiration, circulation) can only be measured if the animal is maintained in pens (so that it cannot move other than standing/lying), at a thermoneutral temperature (so that it is not using energy to keep warm or cool down) and fasted (so that it is not using energy to digest food). The animal is also not growing, lactating or maintaining a pregnancy.

The heat produced by such an animal is called the fasting heat production (FHP) or basal metabolic rate (BMR). This FHP is the net energy consumed for maintenance and is closely related to the body weight (W) of the animal. For sheep, the equation is as follows: FHP ( MJ / day ) = 0.23W 0.75 where W is weight in kilograms. The sex of the animal has an effect, however, because males have a higher basic metabolic rate than ewes. Age also has an effect, so the final equation for FHP is as follows:

(

FHP ( MJ / day ) = S ´ 0.23W 0.75 ´ e -0.03Age

)

where S = 1.0 for females or 1.15 for males and age is measured in years. Given that FHP is effectively the NE required for maintenance and we want to use ME as the unit, we need to correct it for the efficiency of utilisation of the ME for NE (k factor). This value depends on the feed quality—highquality feeds are used more efficiently than low-quality feeds. The relationship between efficiency of use of ME for NE (k factor) is described by the following equation: K m = 0.02MD + 0.5 where MD is the metabolisable energy density of the diet in units of MJ/kg DM.

43

3. 2 E n e rg y a n d P ro t e i n R e qu i r e m e n t s of G r a z i ng Sh e e p

Typical values for a wide range of diets lie between 0.62 and 0.74. Most feeds for grazing sheep are used with an efficiency of about 70%, so the ME required for maintenance is close to FHP/0.70. While the decision support software systems available for managing grazing sheep take all the aforementioned factors into account, for practical sheep feeding purposes, the energy required for maintenance can be easily and quite accurately estimated using the following equation: ME m ( MJ / day )   =   0.13 x W + 1.2

(2)

This equation was derived by MAFF (1975)4 assuming a constant efficiency of utilisation of ME for NE, with no sex or age effects and no scale effect of body weight. Despite all these assumptions, the effects on actual MEm required are very small indeed. A comparison of the values from equation (2) with the more detailed models of NRC (2007)5 across a range of diets and body weights showed relative agreements of 0.95–1.10, with an average close to 1.0. From a practical feeding viewpoint, equation (2) can be used to quickly estimate the ME requirement for the maintenance of grazing sheep before considering their requirements for grazing activity and homeothermy. Box 3.1 The maintenance energy requirement of a non-pregnant, nonlactating sheep before considering requirements for grazing activity and homeothermy (from equation 2). Sheep of 50 kg bodyweight Sheep of 60 kg bodyweight Sheep of 70 kg bodyweight

7.7 MJ of ME

9.0 MJ of ME

10.3 MJ of ME

3.2.4 Maintenance Energy Requirement of Actively Grazing Sheep The energy costs of grazing relate to the body weight of the sheep, the distance it walks, the steepness of the topography and the energy costs of eating and ruminating. These are shown in Table 3.1.

For a 60 kg sheep grazing on hilly terrain for 8 hours/ day, ruminating for 8  hours/day, walking, say, 10  km/day and climbing 500 metres, the additional ME required above maintenance would be about 2.9 MJ/day, which is about 30% higher than the maintenance energy it would require if it was housed in a pen. Obviously, sheep grazing very sparse pastures will graze considerably longer than those on highdensity pastures, and their ME requirement will be about 40% higher than that of their penned counterparts. A sheep grazing very sparse pastures on very hilly country will require up to 80% more energy than its penned counterpart. Box 3.2 Depending on the terrain and the extensive nature of the grazing system, it can be assumed that grazing activity adds 2–4 MJ of ME to the basic daily requirements of grazing sheep.

3.2.5 Maintenance Energy Requirements of Cold-Stressed Sheep The maintenance energy requirement of sheep grazing in cold environments is increased dramatically, particularly if there is a combination of rain and wind such that the wind chill factor is increased. The temperature below which additional heat is required to achieve homeothermy is called the lower critical temperature (LCT). LCT depends on age, fleece cover, body condition (fatness), level of feeding, rainfall and wind speed. The higher the LCT, the more susceptible the sheep is to cold stress, hypothermia and death. Table 3.2 shows a small subset of LCTs for a few scenarios of age, condition and coat cover. The combinations of wind speed, rainfall, body weight and coat depth are considered in an equation to estimate the additional ME required to produce additional heat below the lower critical temperature. The matrix of wind chill factors, coat cover and body condition are available

Table 3.2 Lower Critical Temperatures (°C) of Sheep in

Dry, Still Air

Table 3.1 Energy Costs of Grazing Activities in

Kilojoules (kJ)

AGE

CONDITION

WOOL COVER

LCT (°C)

Lamb

Newborn

28

ACTIVITY

ME COST (kj/kg BODY WEIGHT)

Lamb

1 month

10

Standing

10 kJ

Adult

Maintenance

Shorn

25

Changing body position

0.26 kJ

Adult

Fasted

Shorn

31

Walking (horizontal)

2.6 kJ/km

Adult

Fully fed

Shorn

18

Walking (vertical)

28.0 kJ/km

Adult

Maintenance

50 mm

9

Eating

2.5 kJ

Adult

Maintenance

100 mm

−3

Ruminating

2.0 kJ

Source: Adapted from NRC (2007).5

44

CHAPTER 3: Energy and Protein Nutrition of Grazing Sheep

in NRC (2007)5 and are estimated in GrazFeed®.6 Under practical feeding conditions, however, the following considerations are relevant: • Sheep on higher levels of feed (for example, lactating ewes) produce more heat from ruminal fermentation and are therefore less susceptible to cold stress (lower LCT) than sheep at maintenance levels of feeding. • Neonatal lambs are particularly susceptible to hypothermia. • At the same level of energy intake, roughages produce more heat than concentrates (lower k m values). • Sheep off-shears are particularly prone to cold stress and hypothermia and should be protected from wind and rain by shedding or paddock shelters.

3.2.6  Metabolisable Energy Requirements for Gestation In the first trimester (days 0–50) little additional energy is required to sustain pregnancy, as the placental and foetal growth demands are small. In the mid-trimester (days 50–100) placental growth is rapid but foetal growth is low. In the last trimester placental growth is low but foetal demands are increasing exponentially, doing so at a higher rate in multiple-bearing than in single-bearing ewes. The additional ME required for gestation in single- and twinbearing ewes is shown in Table 3.3. These figures are derived using an efficiency of utilisation of ME for NE for gestation of a constant 0.133 (Kp). A  60 kg ewe grazing at pasture has an ME requirement for maintenance of about 11.0 MJ/day, so these represent significant increases in the ME requirement to maintain the pregnancy. With total ME required increasing over the last month of gestation from 13.6 to 16.3 MJ/day (for the single-bearing ewe) and from 14.0 to 19.0 MJ/day (for the twin-bearing ewe), the ewe will become increasingly unable to consume sufficient feed to achieve these levels of energy intake because the placenta and foetus encroach on the rumen and reduce its total capacity—and do so before ruminal stretch

receptors are stimulated. For low- to medium-quality roughage diets of, say, 7–9 MJ/kg DM, matching this level of energy consumption would require an intake of 1.7 to 2.0 kg (single) and 1.9 to 2.4 kg (twin)—levels which substantially exceed the maximum intake of pregnant ewes even if pasture availability is not limiting. The ewe will then make up the shortfall by mobilising body reserves, but too large a shortfall due to low-quality feed or low pasture biomass will result in rapid mobilisation of reserves. The consequence is a decline in body condition score which, if too severe, increases the risk of pregnancy toxaemia and has serious consequences for the probability of survival of the neonatal lamb, particularly in multiple births. Ewes well fed in the last trimester, in good body condition at lambing (condition score 3) and producing lambs of 4 to 5.5 kg have lower lamb mortality than ewes of lower condition score producing lighter-weight lambs. The relationship between ewe condition score and lamb survival is much stronger for twin lambs than for singles (Figure 3.5).7 Ewes in good condition at lambing, and receiving adequate nutrition at the same time, produce more colostrum and more post-colostral milk than ewes in poor condition or that are underfed at lambing, so the implications for the ewe and her lamb(s) of underfeeding in late pregnancy extend well beyond the perinatal period alone. (See also Chapter 7.)

Box 3.3 Ewes require additional ME intake to meet their energy requirements in late pregnancy. Four weeks before lambing, a 60 kg ewe requires an additional: 2.6 MJ of ME for a single foetus 3.9 MJ of ME for two foetuses

3.2.7  Metabolisable Energy Requirements for Lactation The efficiency of utilisation of ME for lactation depends on diet MD as follows: K l = 0.02MD + 0.4

Table 3.3  Additional ME (MJ/day) Required for Gestation in Single- and Twin-Bearing Ewes Giving Birth to Lambs Weighing 4.0 kg (Singles) and 3.0 kg (Twins) WEEKS PRE-TERM 12

8

6

4

2

0

Singles

0.4

1.1

1.7

2.6

3.8

5.3

Twins

0.6

1.7

2.6

3.9

5.7

8.0

where MD is the metabolisable energy density of the diet (MJ/kg DM). For most sheep diets, the K l value will be between 0.56 (for a medium-quality pasture hay) to 0.64 (for a highquality concentrate ration). The ME required for each litre of milk depends on its fat content, but, assuming a constant fat content of sheep milk of 80 g/kg and an average K l of 0.60 for most sheep rations, the ME required for milk production is approximately 8.1 MJ/kg milk.

3. 2 E n e rg y a n d P ro t e i n R e qu i r e m e n t s of G r a z i ng Sh e e p

45

Figure 3.5  Ewes lambing at higher body condition scores have higher lamb survival than those at lower scores. Single lambs—red line; twin lambs—blue line. The effect of condition score on lamb survival is greater for twin lambs than singles. Source: Redrawn from Ewe Management Handbook and produced with permission from Lifetime Wool.

Ewes in good condition at lambing will initiate lactation at levels approaching 2 kg of milk per day. There are breed differences—BL × Mo ewes produce more than purebred Mo ewes—and ewes with multiple lambs produce more milk than ewes with one lamb. (See Chapter 7.) These high levels of lactation are not sustained and fall markedly after two to three weeks. (Dairy breeds of sheep are an exception to this.) The amount of feed that a ewe can consume each day (the maximum feed intake) increases substantially at lambing and during early lactation. The magnitude of the increase is influenced by the number of lambs, and the timing of the increase lags behind the rise and fall in milk yield after lambing, with maximum feed intake peaking about six weeks after lambing. Consequently, under most commercial conditions, ewes expend more energy during early lactation than their diet supplies, and they mobilise tissue reserves to fund the energy deficit for milk production. The fall in condition score is much greater for ewes with multiple lambs than for those with single lambs. The ability of the ewe to meet the deficiency by fat mobilisation depends on her condition score at lambing. Once lactation levels decline to lower levels, ewes on good-quality pasture can maintain body condition. For 60 kg ewes feeding single lambs at pasture and producing 1 kg of milk per day, an additional 8 MJ of ME is required on top of their maintenance requirement of about 11 MJ/day (total = 19 MJ/day). For ewes feeding twins (and producing

1.5 kg milk/day), the additional requirement for milk production is about 12 MJ/day (total  =  23 MJ/day). Most medium- to high-quality pastures (>10 MJ/kg DM) will provide this amount of energy in the daily intake of about 2.1 kg/day for a 60 kg ewe. Most Merino ewes on good-quality pastures with pasture availability of 1300 to 1500 kg (feed on offerb) will achieve growth rates of single lambs approaching 200 g/day (Figure 3.6).7

3.2.8  Guidelines for Managing Pregnant Ewes to Ensure High Rates of Lamb Survival and Lamb Growth to Weaning The following guidelines for ewes approaching lambing are designed to minimise pregnancy toxaemia, to ensure high lamb survival rates and to achieve high growth rates of lambs to weaning: • Twin-bearing ewes should be at a condition score >2.7 and preferably 3.2 by lambing. To achieve this, feed on offer should be >1000 kg DM/ha of good-quality green pasture. If pasture is less than this or if the pasture quality is poor (10.5 MJ/kg) should be fed to achieve condition scores of about 3.

 The term feed on offer is described on page 54.

b

46

CHAPTER 3: Energy and Protein Nutrition of Grazing Sheep

Figure 3.6  The impact of feed on offer on the growth rate of Merino single lambs and twin lambs to weaning. Source: Reproduced with permission from Lifetime Wool.

• Ewes with a condition score 10 g/day) occurred only when blood selenium levels of a sample of lambs in the flock were less than 130 nmol/L. Again, reference to Table 4.4 suggests that treatment of animals in a flock with a mean in the ‘marginal’

range is unlikely to be justified unless it is anticipated that selenium levels will continue to fall.

4.3.10

Selenium Toxicity

Acute selenium toxicity occurs following the administration of selenium at excessive dose levels or when an amount of selenium which is normally considered appropriate is given to sheep with blood levels of selenium already elevated by previous supplementation. Young lambs may be particularly susceptible to selenium poisoning due to incomplete rumen development.77 In older lambs, deaths within 2–48 hours of treatment have been frequently reported following doses of sodium selenite by injection or by mouth at 1.0 mg Se/kg.78 Dosages

88

CHAPTER 4: Clinical Aspects of Trace Element and Vitamin Nutrition

Figure 4.5  A reference curve for selenium predicting the increase in liveweight gain which can be expected by supplementation of animals at varying levels of selenium nutritional status. Source: Kym A Abbott. Based on data from Grace and Knowles (2002).73

exceeding 10 times the recommended level are considered very likely to cause toxicity and, on some occasions, deaths have occurred at lower levels of overdosing. There is significant variation in the susceptibility of individual sheep to selenium. Depending on the degree of overdosage, often only a minority of a flock shows signs. It is suggested that stresses, such as forced exercise after dosing or low-protein diets, increase the likelihood of toxicity, clinical signs and deaths. On other occasions, losses in medicated sheep flocks and cattle herds can be very extensive. An accidental overdosing with parenteral sodium selenite of young cattle in New Zealand, in which they received 0.5 mg/kg instead of an intended dose of less than 0.1 mg/kg, led to the deaths of 376 animals from the treated herd of 557. Deaths commenced within a few hours of treatment and continued over five weeks. The animals had been stressed by recent weaning, frequent mustering, wet weather and concurrent vaccination.79 Signs of toxicity in sheep include restless behaviour, abdominal pain, excessive salivation and blindness. Death occurs within 1–5 days of the toxic dose. At necropsy, there is excessive pale yellow or clear fluid in the pleural cavity and pericardial sac. The lungs are oedematous, fail to collapse and ooze fluid when cut. The myocardium is pale, and some skeletal muscles may also be affected and pale.80 Administration of selenium at levels closer to the recommended level of 0.1 mg/kg, if repeated too frequently, may also cause toxicity. Administration of 5 mg Se as sodium selenite by mouth to adult sheep, repeated fortnightly, led to the deaths from selenium toxicosis within 5

to 11 months. Sheep which were on low-protein diets were found to be more susceptible to toxicosis than those on high-protein diets.81 Chronic selenium toxicity occurs under natural conditions in sheep grazing seleniferous plants (seleniumaccumulating plants). These plants occur in some parts of North America (North and South Dakota, Wyoming). In Australia, selenium-accumulator plants occur only in regions of northern Australia. Two forms of chronic toxicity are reported—blind staggers and alkali disease. Blind staggers is caused by the consumption of seleniferous plants containing compounds from which selenium is readily extractable in inorganic form. Alkali disease occurs in animals consuming seleniferous grains or plants containing 5 to 40 ppm of selenium (5 to 40 mg/kg DM) in which the selenium is firmly bound to proteins. Clinical signs of alkali disease include lameness, hoof malformations and sloughing, loss of hair, loss of appetite and liver cirrhosis.

4.4  VITAMIN E DEFICIENCY 4.4.1 Introduction Vitamin E is an essential nutrient in the diet of ruminants and is ingested preformed as a component of plant tissue. Actively growing and photosynthesising pastures and forages are relatively rich in the vitamin, but dead pasture, stubbles, grain and hay have a low vitamin E content. During periods of high dietary intake of the vitamin, sheep are able to build up stores in body tissues, but if deprived of access to green feed for a period of several months, the reserves become exhausted and a deficiency syndrome

4.4 Vi ta m i n E D e f ic i e nc y

develops. If sufficiently severe, deficiency of vitamin E leads a nutritional myopathy, characterised by the necrosis of skeletal muscle tissue. Vitamin E deficiency-induced nutritional myopathy can develop in sheep of practically any age, but the most common expression of disease in Australia occurs in weaner sheep—aged 6 to 12 months—in late summer and early autumn in parts of the country which have long periods without rain from late spring to autumn. In the strongly Mediterranean climate of southern Western Australia the syndrome has been known as weaner nutritional myopathy (WNM). The term vitamin E refers to a group of eight tocotrienol and tocopherol compounds, each with alpha, beta, gamma and delta isomeric forms. Ruminant diets contain a mixture of these compounds, but the dominant one which is responsible for most of the biological activity of the vitamin E group is a-tocopherol. One international unit (IU) of vitamin E activity is equivalent to the activity of 1 mg a-tocopheryl acetate or 0.67 mg a-tocopherol. The role of vitamin E as an antioxidant was described in the previous section with the physiological functions of selenium (Section  4.3.2). In brief, vitamin E protects the functional integrity of cellular membranes by preventing lipid peroxidation of polyunsaturated fatty acids (PUFAs). Its role is particularly important in the tissues of skeletal and cardiac muscles, protecting against the tissue destruction which leads to myopathy. While the selenium-containing enzyme GPx1 plays a supportive role in protecting muscle cells against peroxidation, it cannot substitute for vitamin E. Less is known about a different selenium-containing enzyme—phospholipid hydroperoxide glutathione peroxidase (PHGPx)—which has an antioxidant role more closely associated with vitamin E. While it is clear that selenoenzymes cannot fully compensate for a lack of vitamin E, and that myopathy due to vitamin E deficiency can occur in animals with adequate selenium nutrition, it is likely that a very low selenium status increases the risk of severe myopathy in vitamin E deficient animals.

4.4.2  Dietary Sources and Requirements of Vitamin E In order to maintain adequate tissue levels, adult sheep require at least 10 to 15 mg of vitamin E per kg of feed DM per day under normal grazing conditions and substantially more during periods of environmental stress and high PUFA intake. Intake requirements are greater in sheep on high-concentrate diets because of an increased rate of ruminal degradation of vitamin E, probably through its involvement in the hydrogenation of dietary PUFAs within the rumen.

89

Most fresh green forages contain about 50 mg α-tocopherol per kg DM with levels in grasses usually higher than those in legumes. Losses occur during sun curing, so levels in hay are substantially lower than those in pasture. Vitamin E levels are also low in dry, senesced pastures, stubbles without green weeds, cereal grains and lupin grain, and, in the case of stored feeds, they decline over time. Cereal grains typically contain about 8 mg/kg DM. During periods when vitamin E intake is above requirements, concentrations in plasma, liver, adipose tissue, muscle and other tissues all increase to high levels. On deficient diets, the tissue concentrations fall more quickly from liver than from muscle and plasma, but bodily reserves as a whole can decline from high levels to a deficient state over a period of about 12 weeks.82 Lambs are born with levels of vitamin E in the liver and plasma lower than those of their dams. There is very little placental transfer of vitamin E to the foetal lamb, but if ewes are adequately nourished with vitamin E, colostrum is a rich source and plasma and liver levels in lambs rise soon after suckling. Post-colostral milk also provides vitamin E but at concentrations only one-third to one-half of the concentration in colostrum. Deficiencies of the vitamin occur when sheep have insufficient green feed in their diet. The climate in the winter-dominant rainfall zones of southern Australia frequently produces extended periods without pasture growth over summer and autumn. By autumn, the sheep’s tissue reserves of vitamin E are exhausted. Vitamin E deficiency myopathy is most commonly reported in weaner sheep (6 to 12 months old) grazing dry cereal stubble paddocks or dry pastures for periods exceeding two months. Weaners born in the previous autumn–winter–spring period are more likely than adults to be affected, probably as a consequence of inadequate opportunity to create reserves of vitamin E in the first few months of life before pasture senescence. Vitamin E-induced myopathy in lambs is not unique to the weaner age group. Nutritional myopathy with sudden death of suckling lambs has occurred when pregnant and lactating ewes were fed a selenium-adequate wheat and barley straw-based diet, without vitamin E supplementation, during a drought.83 A deficiency of the vitamin can also develop in sheep of any age fed for extended periods on grains and hay without green feed.84

4.4.3  Clinical and Necropsy Signs of Vitamin E Deficiency The nutritional myopathy induced by a deficiency of vitamin E has clinical and necropsy signs similar to those of the myopathy caused by selenium deficiency but occurs in sheep with an adequate selenium status.51,85 The condition

90

CHAPTER 4: Clinical Aspects of Trace Element and Vitamin Nutrition

is so similar to the myopathy of lambs grazing seleniumdeficient green pastures that this myopathy is also called white muscle disease by some workers in the field. In weaner sheep grazing stubbles or dry pastures, clinical signs and deaths may be first observed two to three days after mustering but can occur spontaneously in the paddock, becoming evident when sheep are disturbed. Clinical signs include weakness; a staggering or shuffling gait with stiff, flexed limbs; muscle trembling; inability to stand; sternal or lateral recumbency with paddling; and frothing from the mouth and nostrils. It can occur in sheep which are in good condition score. Mortality rates can approach 10% of affected mobs.85 Not all sheep which show signs of myopathy deteriorate further. Early signs of hind limb stiffness or a hunched back indicate skeletal muscle damage, but if stresses are minimised and treatment is provided at an early stage, animals can recover completely.86 The myopathy can be so mild as to be subclinical with the tissue damage only detectable with clinical pathology or by histopathology.87 Stressors other than exercise may be important in precipitating myopathy. These include concurrent lupinosis, annual ryegrass toxicity and prolonged low selenium intake. At necropsy, lesions are found consistently in skeletal muscles and frequently also in cardiac muscle.88 Hind limb lesions involve those muscles of the quadriceps groups which contain a high proportion of type II fibres—the tensor fascia lata, rectus femoris and vastus lateralis. These muscles appear to be less well protected against myopathy than those composed predominantly of type I fibres such as the vastus intermedius, which is less commonly affected.87 Muscles of the forelimb (particularly the triceps brachii) and back (psoas major) may be involved. In the heart, lesions appear as cream-white plaques on the endocardium of the ventricles, the right ventricle being more frequently affected than the left.85 The skeletal muscle lesions appear as pale areas which may involve the whole muscle or be restricted to small patches in the muscle. Lesions may also be seen in muscles of the tongue and diaphragm. On gross examination the lesions in skeletal muscles are less striking than those of white muscle disease caused by selenium deficiency and often require histological examination to confirm their presence.89 In some cases lesions are only detected histologically. Myoglobinuria is generally not present85 but does occur in some cases.

enzymes in plasma) is very common, and unrecognised cases may contribute to weaner mortalities following prolonged periods of dry weather over summer and autumn.51 Unless clinical disease develops—indicated by reluctance to move and graze normally—there appears to be no measurable effect of subclinical disease on liveweight or wool productivity of affected sheep.90

4.4.5  Clinical Pathology and Confirmation of Deficiency Both plasma and liver α-tocopherol concentrations provide a good indication of vitamin E nutritional status. When vitamin E tissue levels are declining, the concentration in the liver declines faster than that in the plasma, suggesting that the liver has a role in moderating the decline in other tissues.82 Plasma levels of muscle enzymes are useful in the diagnosis of nutritional myopathies. An elevated plasma creatine kinase (CK) is specifically indicative of muscle damage because the enzyme is normally distributed only in skeletal and cardiac muscle. A low value for plasma CK, however, does not rule out myopathy because plasma levels fluctuate widely in sheep with subclinical WNM and the enzyme has a half-life of only a few hours. Because of the variability in plasma CK through the course of an episode of myopathy, it is advisable to take blood from a sample of five or more animals in the affected group and note the proportion which has high plasma CK levels. Measurement of plasma alanine amino transferase (ALT) is also recommended, alone or in conjunction with that of CK. Aspartate amino transferase (AST) and lactate dehydrogenase (LDH) are sensitive indicators of muscle damage but are not specific—they are also raised when liver damage occurs.86,91 During periods of adequate nutrition, vitamin E concentrations normally lie in the range of 1 to 4 mg/L for plasma and above 1.8 mg/kg wet weight for liver. Levels of 0.6 mg/L and 1.2 mg/kg wet weight for plasma and liver are considered thresholds below which myopathy is likely to develop. CK levels between 400 and 1200 U/L are indicative of mild to moderate muscle damage and are usually associated with plasma vitamin E levels of 0.6 mg/L or lower. Levels of vitamin E, CK and AST which are expected in sheep with severe myopathy are shown in Table 4.2.

4.4.4  Subclinical Deficiency of Vitamin E

4.4.6  Treatment and Prevention of Deficiency

In the southern sheep-raising areas of Western Australia, subclinical weaner nutritional myopathy due to vitamin E deficiency (detected by elevated concentrations of muscle

Affected sheep should be treated with oral or parenteral vitamin E and moved as quietly and slowly as possible. The oral route is preferable to parenteral routes of

4.5 D i f f e r e n t i a l D i ag nosi s of Myopat h y

Table 4.2 Expected Plasma Levels of Vitamin E and Muscle Enzymes (in Units per Litre (U/L)) in Weaner Sheep Suffering from Subclinical and Clinical Nutritional Myopathy Caused by a Deficiency of Vitamin E51,85 LIVER PLASMA CONCENTRATIONS CONCENTRATIONS HEALTH VITAMIN E VITAMIN CREATINE ALANINE ASPARTATE CONDITION (𝝻g/g E (mg/L) KINASE AMINO AMINO OF SHEEP WET (CK) (U/L) TRANSTRANSTISSUE) FERASE FERASE (ALT) (U/L) (AST) (U/L) Normal 3–40 (access to green feed)

1–4

70–300

Mild 1.0–1.8 subclinical myopathy

0.5–0.7 400–1200 25–80

150–270

Severe 1200

1–20

>80

50–150

administration when treating clinically affected animals because it more quickly raises plasma and liver vitamin E levels. A  drench of a-tocopherol acetate (120 mg per kg liveweight, in aqueous suspension) will raise plasma levels within 1 day and liver levels within 7 days. To avoid mustering and yarding sheep which are at risk of clinical WNM, vitamin E as a water-miscible powder can be sprayed onto grain used as supplementary feed.51 Repeated oral treatments at 6- to 8-week intervals are necessary until the sheep have access to green feed.92,93 For housed sheep, vitamin E can also be administered in the feed at the rate of 100 mg/kg of feed DM per day. Intramuscular injection of vitamin E in an oily base has been reported to give longer periods of elevated plasma a-tocopherol in most field situations than oral administration does, suggesting that IM injections are preferable to oral routes for prophylaxis.94 Intramuscular injections, however, may cause a local myopathy, and the vitamin may become sequestered in regional lymph nodes for extended periods.95 Because of uncertainty about absorption rates and the possibility of tissue damage from injectable products, oral administration is recommended for prophylaxis as well as therapy. In the absence of any productive benefits of administering vitamin E to weaners with mild subclinical nutritional myopathy, routine supplementation of weaners over summer and autumn is not usually considered cost effective unless more severe or clinical WNM is likely to occur.92

91

The decision to provide prophylactic treatment to weaner sheep grazing pastures or stubbles in summer should be made on the basis of the previous two to three months’ rainfall and, if practicable, monitoring of plasma vitamin E and CK levels in a sample of the flock. Similar decisions should be considered for pregnant ewes being fed grain and hay during drought conditions to ensure that the ewes have adequate vitamin E and are able to transfer sufficient vitamin E to their lambs in colostrum and milk. Supplementation of ewes with vitamin E during gestation has a very limited effect on the vitamin E levels in the presuckling neonate but does increase the concentration of the vitamin in colostrum.96 Supplementation is less effective at boosting mammary gland secretion of vitamin E if it is discontinued before parturition, even if liver reserves of the vitamin in ewes are within a normal range.97 If lactating ewes and their lambs do not have access to feed with adequate vitamin E levels, supplementation of the ewes should continue, either from parenteral depots or continuing oral medication.

4.5 DIFFERENTIAL DIAGNOSIS OF MYOPATHY The disturbances in gait of affected sheep may, at first glance, resemble those of arthritis, laminitis and infections of the foot, but these can be ruled out by clinical examination. In the live animal, swelling and hardness of the muscles of the thigh may be detected by palpation. In differentiating causes of myopathy, a history of access to green feed effectively rules out vitamin E deficiency, but clinical pathology, including estimations of plasma selenium, GPx and vitamin E, is useful. At necropsy, a combination of histopathology and clinical pathology will confirm a diagnosis. Lupinosis, although primarily a hepatotoxicity, has also been associated with a myopathy in sheep in Western Australia (lupinosis-associated myopathy, LAM).98 LAM is not preventable with selenium or vitamin E, although it has been proposed that the pathophysiology of the muscle damage is similar to that of WMD and WNM and is a consequence of the high PUFA and low vitamin E and selenium levels in lupin crop residues and lupin grain to sheep which are predisposed by the hepatotoxic effects of phomopsin.99 Sheep with LAM have a history of recent exposure to lupin stubbles, and jaundice is usually present in at least some of the flock which have had similar exposure to phomopsin. At necropsy, varying degrees of liver damage are detectable either grossly or histologically. Sudden death, while a feature of outbreaks of WMD/WNM, is not so common with LAM.98

92

CHAPTER 4: Clinical Aspects of Trace Element and Vitamin Nutrition

The estimation of muscle and liver enzymes and blood biochemistry can also assist the differentiation between syndromes of myopathy with liver damage and those without. In lupinosis, liver damage leads to elevation of plasma gamma-glutamyl transpeptidase (GGT) and bilirubin, both conjugated and unconjugated. In myopathies without liver damage, GGT and bilirubin are normal, while CK and ALT are elevated. Plasma AST is raised with both muscle and liver damage.100 Sheep with congenital progressive ovine muscular dystrophy also develop a stiff hind limb gait. Affected sheep fail to thrive and their locomotor deficit worsens, so that they are culled or die of other causes before they are 2  years of age.101 The condition is a true dystrophy rather than a degeneration as in WMD, WNM and LAM, and a distinctive feature observed post-mortem is the involvement of the vastus intermedius muscle, which is not significantly involved in the myopathy of vitamin E deficiency. The disease is rare. Exertional rhabdomyolysis has also been reported in sheep, following prolonged chasing102 or poorly controlled mustering with dogs or motorbikes. A  deep red urine from myoglobinuria is characteristic of exertional rhabdomyolysis. Eating the seeds of mature stands of Ixiolaena brevicompta (common names plains plover daisy, billy button) in the flood plains of Queensland and western New South Wales has been associated with clinical signs of hindlimb weakness, staggering and collapse and extensive mortalities. Affected sheep have a severe degenerative myopathy with high plasma levels of CK and AST. Degenerative changes also occur in the kidney, liver and central nervous system.103 Chapman (1990)104 also includes monensin toxicity, poisoning with the plant Cassia occidentalis (common name coffee senna) in Queensland, ischaemic myopathy, trauma, snake bite, clostridial myositis and cereal grain-associated myopathy in the diagnostic considerations for myopathies of sheep.

4.6  IODINE DEFICIENCY (INCLUDING GOITRE AND HYPOTHYROIDISM) 4.6.1 Introduction Iodine is essential for thyroid hormone production. A persistent dietary deficiency of iodine leads to iodine deficiency disorder (IDD), the clinical manifestations of which are the result of hypothyroidism—an inadequate secretion of thyroid hormones from the thyroid gland. Apart from some subclinical impacts of IDD on reproductive parameters in adult ewes which are discussed further herein, the major effects of IDD in sheep are on the health and viability of newborn lambs.

The thyroid hormones are tetra-iodothyronine (also known as thyroxine or T4) and its more active derivative triiodothyronine (T3). They have very wide-ranging effects on metabolism in many body tissues and are essential for the normal development of the foetal brain, integument, skeleton, heart and lungs. They are critically important in the adaptation of the newborn animal to life outside the uterus. A brief revision of the normal physiological activity of the thyroid gland will be helpful in understanding the circumstances which lead to IDD and the ways that it may be diagnosed, prevented and treated.

4.6.1.1  Physiology of the Thyroid Gland The thyroid gland is composed of millions of follicles, each of which is formed within a layer of epithelial cells—the follicular cells. The iodine-free glycoprotein thyroglobulin is produced in the follicular cells and accumulates within the lumen of the follicles. The thyroglobulin molecule consists of a protein chain, along which are attached multiple copies of the amino acid tyrosine. Iodine enters the epithelial cells of the thyroid follicles in the form of iodide ions, moving from the blood by an active transport mechanism against a strong concentration gradient. Iodide concentrations in the blood are generally very low, but the thyroid follicular cells are very efficient at extracting iodide from the blood, provided there are no other, similar-sized single-charged anions competing for the transport mechanism. Once in the follicular cells, iodide ions are moved into the follicular lumen where, in the presence of the enzyme iodide peroxidase, inorganic iodide is oxidised to an active form of iodine which binds readily with the tyrosine residue of thyroglobulin molecules. The iodination of tyrosine and formation of an iodine-containing organic compound is referred to as the organification of iodine. The process of iodination leads first to the formation of 3-monoiodotyrosdine (MIT), and then, with the addition of a second iodine atom, the formation of 3,5-diiodotyrosine (DIT). Coupling of two iodo-tyrosine molecules then leads to the formation of either the tri-iodinated molecule triiodothyronine (T3) or the tetra-iodinated thyroxine (T4). Still linked to the parent protein chains, these hormones remain in the thyroglobulin colloid of the thyroid gland as a store of the hormones, with some moving into the follicular cells prior to secretion into the bloodstream. Within the follicular cells, T3 and T4 are detached from the protein molecule and move into the blood, where most of the hormone circulates in association with a protein carrier and lesser amounts circulate as free T3 and T4. If blood levels of T3 and T4 fall to low levels, there is an increased secretion from the pituitary gland of

4. 6 Iodi n e D e f ic i e nc y ( I nc lu di ng G oi t r e a n d Hy p o t h y roi di sm)

thyroid-stimulating hormone (TSH). TSH stimulates the activity of follicular cells, leading to increased uptake of iodide from the blood, if available, and increased production of T3 and T4. When T3 and T4 levels return to normal, TSH secretion is suppressed in a self-regulating feedback system. If, however, follicular cell stimulation is unable to adequately increase thyroid hormone secretion, the animal becomes hypothyroid, TSH levels remain high, and stimulation of the follicular cells continues. The result is hypertrophy and hyperplasia of the thyroid follicular cells and an increase in the size of the thyroid gland, sometimes to 10 times or more its normal size. An enlarged thyroid gland is called a goitre. Hypothyroidism and goitre can occur as a result of an uncomplicated dietary deficiency of iodine but can also occur as a result of the presence of substances which interfere with the uptake of iodide from the blood by the thyroid follicular cells or with biochemical processes which result in the incorporation of iodine into the organic molecules, leading to the production of T3 and T4. Because these substances lead to hypothyroidism and, if persistent, to the development of goitre, they are referred to as goitrogenic substances.

4.6.2 Goitrogens The most important goitrogens affecting sheep are derived from glucosinolates in plants of the Brassica genus, which includes forage rape, dual-purpose canola, kale (also known as choumoellier), turnips and swedes, cabbage, cauliflower and broccoli (Box 4.2). Similar compounds also

93

occur in species of other plant genera, some of which occur as weeds in Australian pastures. Glucosinolates function in plants as components of a defence mechanism against pests based on the production of isothiocyanates (mustard oils) and other agents when plant tissue is damaged. There is a very wide range of metabolites formed as breakdown products of the glucosinolates, but the principal compounds of animal health significance are isothiocyanates, thiocyanates, thioamides, oxazolidine-2-thiones and nitriles. The principal products of glucosinolate breakdown are described in Table 4.3, and the pathways of glucosinolates degradation are illustrated in Figure 4.6. Some of the compounds participating in the glucosinolate–myrosinase system with implications for the health of grazing ruminants are summarised in Box 4.1. Glucosinolates are chemically stable in the plants, but when the plants are eaten and the plant cells are disrupted, the plant enzyme myrosinase is freed from its containment within specialised plant cells and causes rapid breakdown of the glucosinolates. The process starts immediately after the plants are eaten and chewed and continues with the on-going tissue breakdown in the rumen and during rumination. It is possible that myrosinase is also produced by bacteria in the ruminant digestive tract, adding to the ingested sources of myrosinase. The amounts and classes of compounds that are produced depend on the types and amounts of glucosinolates in the ingested plants and, to some extent, the nature of the rumen environment. The two classes of compounds which are most important as goitrogens are thiocyanates

Figure 4.6  Glucosinolates are common chemicals found in Brassica spp plants. Under the action of the enzyme myrosinase, glucosinolates give rise to a range of substances, several of which—the thiocyanates and oxazolidine-2-thione— are goitrogens.

94

CHAPTER 4: CliniCAl ASPECTS oF TRACE ElEmEnT And ViTAmin nuTRiTion −

and oxazolidine-2-thiones. Thiocyanate, an anion (SCN ) of similar charge and molecular size to iodide, inhibits iodide uptake by the thyroid follicular cells. In addition to blocking iodide uptake, thiocyanates cause the thyroid gland to release any iodine which is not bound with thyroglobulin. While their effect can be readily overcome by the provision of high dietary levels of iodine or iodine supplementation, if iodine intake is low, the iodine levels in the thyroid gland will decline and thyroid hormone synthesis will be compromised. The oxazolidine-2-thiones (OZT), however, have a much stronger antithyroid activity. They do not compete with iodide for uptake by the gland but interfere with steps involved in the organification of iodide—they inhibit the activity of thyroid peroxidase and restrict the production of iodotyrosines and the coupling reactions which lead to the formation of the iodothyronines T3 and T4. They may also inhibit the deiodination of T4 to T3 peripherally. Because their mode of action is similar to that of the antithyroid drugs thiouracil and thiourea, this class of goitrogens is often referred to as ‘thiouracil-like’ or ‘thiourea-like’. This form of antithyroid activity cannot be overcome by the increased availability of iodine but, fortunately, modern forage brassicas are sufficiently low in offending glucosinolates that blocking of iodine organification is usually only partial. Unless iodine intake is also very low, the thyroid gland is then able to produce sufficient thyroid hormones. Each species of Brassica plants contains a wide range—perhaps 20 or more—of different glucosinolates distributed through leaves, stem, flowers and seeds.

Concentrations tend to increase when the plant is subject to attack by pests or other disease agents. The types of glucosinolates and their absolute and relative proportions also vary between plant species and, within the same species, between varieties. The best known of the OZT type of goitrogen is goitrin, derived from the glucosinolate progoitrin, which is often at relatively high concentrations in forage rape. New varieties of forage rape have relatively low levels of both glucosinolates and erucic acid production and are called ‘double-low’ varieties. The low-glucosinolate varieties are more palatable and present lower risks for goitrogenic activity than older varieties. Progoitrin may be present in rapeseed meal. Thiouraciltype goitrogens, including goitrin, also occur in forage kale, swedes and turnips. Thiocyanates can be derived from plants other than those of the Brassica genus. White clover (Trifolium repens), for example, may contain high levels of cyanogenic glycosides. In the rumen, these glycosides release hydrogen cyanide which, in the presence of ruminal sulphur, is rapidly converted to thiocyanate. The goitrogenic potential of white clover pastures is recognised in New Zealand and has been implicated in cases of congenital goitre in the Northern Tablelands of NSW in Australia. There are also other anions which can, like thiocyanate, displace iodide in the battle for uptake from blood. The most likely one to occur naturally in grazing sheep is nitrate, but cases of nitrate leading to clinical goitre in sheep appear to be rare. Nitrate is a very much weaker goitrogen than thiocyanate.

Box 4.1 THE COMPOUNDS PARTICIPATING IN THE GLUCOSINOLATE– MYROSINASE SYSTEM CAN HAVE IMPLICATIONS FOR THE HEALTH OF GRAZING RUMINANTS. CHARACTERISTICS OF SOME ARE SUMMARISED HERE: CHEMICAL

DESCRIPTION

NOTES

Glucosinolates

A group of over 120 different organic anions based on a sulphur-containing glucose moiety (β-D-thioglucose) with a variable side chain derived from an amino acid. While they occur in a number of plant genera, they are a particular characteristic of the Brassica genus. They are stable, non-toxic, relatively inert substances which occur in most tissues of the plant—leaves, stems, roots and seeds.

Progoitrin, gluconapin, glucobrassicanapin, gluconasturtiin, glucobrassican, neoglucobrassican and sinigrin are all examples found in forage brassicas.

Myrosinase

Enzymes of the β-thioglucosidase group, these endogenous plant enzymes cause rapid hydrolysis of glucosinolates and the release of a range of bioactive breakdown products. They are also widespread through the tissues of Brassica spp plants but are maintained in isolation from the glucosinolates until the plant cell structure is disrupted—typically by chewing. The glucosinolate–myrosinase enzyme system forms a potent defence mechanism against herbivores and pests by virtue of the release of isothiocyanates and nitriles.

4. 6 Iodi n e D e f ic i e nc y ( I nc lu di ng G oi t r e a n d Hy p o t h y roi di sm)

CHEMICAL

DESCRIPTION

95

NOTES

Degradation products formed by the hydrolysis of glucosinolates Isothiocyanates

A chemical group of the general structure R-N=C=S, the isothiocyanates are commonly known as mustard oils. The breakdown products of some types of glucosinolates are predominantly isothiocyanates, although they vary in chemical stability and, therefore, persistence. They have a strong, pungent flavour which may deter herbivorous insects from consuming the plants and are natural pesticides. When leached into the soil they act as natural pesticides and fungicides, improving the soil environment for subsequent crops or sown pastures.

An example of a stable isothiocyanate is one known to human diets—allyl thiocyanate— the mustard oil of wasabi. It occurs in horseradish as a breakdown product of sinigrin.

Thiocyanates

A chemical group of the general structure R-S=C=N, these are linkage isomers of isothiocyanate. The thiocyanate ion is a single negative charge anion with similar chemical reactivity to the halides, such as iodide. The breakdown products of some types of glucosinolates are predominantly thiocyanates.

Glucobrassican is an example of a glucosinolate that produces thiocyanate on hydrolysis.

Thiouracil

Examples include 2-thiouracil. The use of thiouracil (as a growth promoter in cattle) is banned in Australia and other countries.

This is a chemical of the thionamides—a group of compounds with a chemical structure which includes a -NC=S sequence. Some thiouracils exist as thyreostatic drugs, but they can also be detected naturally in animals on glucosinalate-rich diets. Oxazolidine-2thione (OZT)

Goitrin, the OZT derivative of the glucosinalate progoitrin, is an example.

OZTs are compounds with the general structure shown. The unstable daughter isothiocyanates of some glucosinolates rapidly develop the cyclic structure of an OZT. Nitriles and epithionitriles

Nitriles are organic compounds with a R-C≡N structure. The inorganic equivalents are cyanides such as HCN, hydrogen cyanide. Nitriles and epithionitriles (nitriles in which the R is a thiirane episulphide moiety) are formed from some glucosinolates under particular conditions influenced by rumen pH, the presence of ferrous ions and the presence of unique specifier proteins.

4.6.3  Hypothyroidism Due to Inadequate Dietary Iodine Sheep ingest iodine in plant material and by soil ingestion while grazing. Generally, the grazing of pastures provides sufficient iodine to meet the requirements of sheep, but the adequacy of iodine nutrition can be affected by geographic region, soil type, seasonal weather patterns, pasture species and the presence of goitrogens. Studies conducted in Australia, New Zealand and other countries examining a wide range of pasture plants have

There is some evidence that daughter nitriles and epithionitriles from progoitrin and sinigrin may be hepatotoxic.

found pasture iodine levels to frequently fall in the range of 0.1 to 1.0 mg iodine per kg of dietary DM. Levels vary markedly between plant species and, within the same species, between sites. Levels in plants also vary through the year, tending to be higher in autumn and winter than in spring. The lower levels in spring may be a consequence of greater pasture growth and a dilution of plant iodine concentrations in the rapidly growing plant. A similar decline in I level occurs in pastures which receive nitrogen fertilisation to boost growth rate.

96

CHAPTER 4: Clinical Aspects of Trace Element and Vitamin Nutrition

Daily requirements of adult sheep on pastures free of goitrogens are estimated to be in the range of 0.2 to 0.4 mg iodine per kg of dietary DM, and if substantial levels of goitrogens are suspected, dietary iodine levels of 2 mg I/kg DM are recommended. It is noteworthy that the expected range of pasture iodine levels is similar to the range of recommended dietary levels, suggesting that periods of inadequate iodine nutrition may be a frequent occurrence for grazing sheep in many places. The ability of adult sheep to develop stores of iodine in the thyroid gland as iodothyronines allows them to maintain adequate thyroid hormone levels during periods of the year when iodine intake is inadequate to meet their requirements, provided the period of dietary deficiency is not too long. While plants may be able to absorb, through foliar translocation, some gaseous iodine from the atmosphere or from iodine in solution in rain, the principal source of iodine for plants is soil. Two factors seem to be critical in determining the amount of iodine in soil. The first of these is the geological origin of the soil—soils of glacial origin having the lowest levels—and the second is a combination of the proximity to the sea and rainfall because volatilised iodine from the sea is dissolved in rain and delivered to the soil through rainfall. Rainfall, however, has a two-edged effect. Iodine is readily leached from soils, particularly from lighter-textured soils, and therefore soil iodine levels tend to be lowest on alluvial and sandy soils105 and in inland mountain areas with relatively high rainfall. Pasture plants are not the only natural source of iodine for grazing sheep. Soil ingested with grazed pasture plays an important role in iodine nutrition. Sheep ingest variable amounts of soil depending on the nature of the soil (they ingest more if the soil is of weak structure) and on the availability of pasture. The amount of soil ingested by sheep at pasture is relatively low in summer and rises after autumn rains (in southern Australia), peaking in late winter and early spring. The stocking density, in terms of the number of sheep per unit of available pasture, also influences the amount of soil ingestion. At high stocking rates, relative to pasture availability, soil intake is higher than at low rates.106 Within the range of normal grazing strategies in Australia, soil intake of sheep could be expected to lie between 50 g and 300 g per day, depending on the factors described earlier. Milk iodine concentrations are a reliable and rapidly responsive measure of daily intake in sheep. By measuring the levels of milk iodine concentrations in ewes grazing pastures in Victoria, Azuolas and Caple (1984)107 were able to demonstrate a seasonal variability in iodine intake over a two year period (1981–1983). In the first year, intakes of iodine (as predicted by milk concentrations) were relatively

low in winter and relatively high in summer. In the second year—a drought year—there was two small peaks of intake—one in May and June (early winter) and one in October–November (spring). While these results are not readily explainable by knowledge of likely levels of soil ingestion or plant iodine levels, they do match the pattern of outbreaks of congenital goitre, which are seen usually in lambs born in the late winter and spring. In Australia, iodine deficiency is most commonly reported from the hills and ranges of Victoria108 and from Tasmania, particularly in the Derwent Valley, Northern and Southern Midlands and parts of New South Wales.109 A survey of thyroxine levels from ewes across four states of Australia found that levels were generally higher in Western Australia and Queensland than in NSW and Tasmania. In NSW, some districts’ levels were well within the normal range, while the lowest levels were associated with the light basaltic soils around Armidale. Dietary iodine deficiency has not been reported from South Australia. In Victoria, outbreaks of goitre and associated lamb mortalities are generally restricted to the high-rainfall districts and to lambs born between August and October,17 but congenital goitre has been reported in a June– July lambing sheep flock in the hill country of northeast Victoria following an unusually wet summer and autumn producing abundant pasture growth through autumn and winter.

4.6.4  Inherited Hypothyroidism and Congenital Goitre An inherited condition causing congenital goitre with high neonatal mortality rates has been described in Merino sheep following a study in 1959–1960 in a number of South Australian flocks. The condition appears to be inherited as an autosomal recessive gene.110 Heterozygous rams are phenotypically normal and therefore the possibility exists that the gene is more widespread than is currently recognised. In homozygous sheep there is a defect in the synthesis of thyroglobulin. Iodine uptake by the thyroid gland is not disrupted. Only homozygous lambs are clinically affected. Most affected lambs have pronounced thyroid hyperplasia (glands in the range of 5 to 200 g) and high circulating levels of protein-bound iodine.111

4.6.5  Hypothyroidism Due to the Ingestion of Goitrogens The use of forage brassicas for feeding ewes during winter is particularly common in New Zealand and becoming more common in Australia. When pregnant ewes graze fodder crops of Brassica spp, the goitrogens they ingest

4. 6 Iodi n e D e f ic i e nc y ( I nc lu di ng G oi t r e a n d Hy p o t h y roi di sm)

act on both the maternal and foetal thyroid glands. The goitrogen most commonly involved is thiocyanate, which interferes with the uptake of iodide by the thyroid gland. If the ewe’s dietary intake (or supplementary supply) of iodine is low and thiocyanate intake is high, there may be a complete cessation of iodide capture by the thyroid glands of both ewe and foetus. In the ewe, if stores of thyroglobulins are adequate, serum levels of T3 and T4 can be maintained within normal ranges for a few months. The foetus, however, is completely dependent on its own thyroid gland for its supply of thyroid hormones and for most of the foetal life has no stores of thyroglobulin in the thyroid gland. A high-goitrogen, low-iodine diet which may have little if any effect on the health of the pregnant ewe in the short term may prevent iodide uptake by the foetal thyroid at a critical stage of foetal development and lead to subsequent clinical hypothyroidism and congenital goitre of the lamb. When exposed to goitrogens of the thiouracil type (such as goitrin), the foetal thyroid is able to accumulate iodine but has an impaired ability to bind iodine to thyroglobulin. With both types of goitrogen, the clinical syndrome is the same—only the levels of iodine in the foetal thyroid are different. In summary, grazing on goitrogenic crops or pastures for one to two months, particularly if over the period when ewes are in the fourth month of pregnancy, creates a significant risk for congenital hypothyroidism in the lambs.

4.6.6  Development of Hypothyroidism Adult sheep maintain stores of iodine in the form of thyroglobulins in the thyroid gland during periods of adequate iodine nutrition. Should iodine intake fall below the levels required to match losses of iodine in urine, then circulating iodine levels will fall to low levels, thyroglobulin synthesis will decline and the thyroid stores will be gradually depleted. Depending on the level of iodine storage and the severity of the dietary iodine inadequacy, it may take up to 5 months before hypothyroidism and thyroid hyperplasia develop in adult sheep.112 In the ovine foetus the levels of circulating thyroid hormones are dependent on the activity of the foetal thyroid gland—under the control of the foetal TSH—and are not related to the levels of maternal circulating thyroid hormone. Circulating maternal iodide crosses the placenta to the foetus through an active transport mechanism, and the output of thyroid hormone from the foetal thyroid gland is dependent on the availability of iodide in the foetal circulation. Maternal T3 and T4 do not cross the ovine placental barrier to any significant degree.113 When maternal dietary iodine fails to meet the ewe’s requirements, both maternal and foetal blood iodide levels fall and the production

97

of foetal thyroid hormone declines. Foetal TSH secretion stimulates foetal thyroid activity, and if thyroid hormone levels remain low, the foetus will develop goitre. The sheep foetal thyroid is normally increasingly active from mid-gestation and, from about day 100 of gestation, will accumulate iodide in the thyroid at rate four or five times greater than that of the ewe. Deficiencies in iodide availability, due to inadequate dietary intake or the presence of goitrogens, becomes critical in the last two months of pregnancy.114 Lambs born to well-nourished ewes are expected to have blood thyroid hormone levels more than twice than those in the ewe.115 Levels in lambs gradually decline after birth over a period of eight weeks, to levels similar to those of the ewes. Lambs born with goitre due to inadequate iodine nutrition of the ewes during pregnancy have levels of thyroxine lower than those of their dams. The ewes giving birth to goitrous lambs may still be euthyroid due to their ability to maintain blood thyroxine levels from thyroid stores over a period of weeks of dietary deprivation.

4.6.7  Effects of Foetal Hypothyroidism Failure of the normal development of the foetal thyroid due to inadequate maternal supplies of iodine is evident by 56 days of gestational age. By day 70, foetuses of iodinedeficient ewes are smaller than those of normal ewes and delays in brain development are evident. The normal development of the foetus through the second half of gestation and the preparation of for extra-uterine life are very strongly dependent on the activity of foetal thyroid hormones. In general, without adequate thyroid hormones, normal protein synthesis and energy production by oxidative phosphorylation is impaired at the cellular level of many body tissues. Foetuses deprived of thyroid hormones have low oxygen consumption, reflecting an inability to generate energy (ATP) at normal levels, despite adequate levels of glucose. The foetal mass increases more slowly; heart, lung and skeletal muscle tissues contain less protein; and bone deposition in the skeleton is reduced. In addition to effects on tissue metabolism, thyroid hormones directly or indirectly contribute to the development, differentiation and maturation of bone, skin including the wool follicles, heart, lung and liver, in the last 70 days of gestational life. A number of the maturational changes in the lung which occur closer to term, in preparation for lung function after birth, are impaired in the hypothyroid lamb. Similar failures in the maturation of tissues and endocrine systems have negative impacts on the cardio-vascular system, hepatic glycogen stores, gluconeogenic pathways and

98

CHAPTER 4: Clinical Aspects of Trace Element and Vitamin Nutrition

brown fat thermogenic capacity, leaving the hypothyroid lamb poorly prepared for life after birth.116

4.6.8  Clinical Signs of Iodine Deficiency A prolonged dietary deficiency of iodine or prolonged grazing on goitrogenic plants without adequate iodine supplementation can lead to an increase in thyroid size and a depression in wool and milk production in adult sheep. If the period of depressed thyroid function occurs to ewes during pregnancy, then the lambs born subsequently may have hypothyroidism and varying degrees of thyroid hypertrophy. The birth of hypothyroid lambs, associated with an unexpectedly high rate of neonatal deaths, is the most common clinical expression of iodine deficiency disorder in sheep flocks. In many cases the hypothyroid lambs have congenital goitre with grossly enlarged thyroid glands, readily palpable in the region of the cranial trachea and visible as a marked swelling in the ventral part of the neck. The length of gestation of hypothyroid lambs is sometimes extended by one to three days, and birthweights tend to be less than those of unaffected lambs. Compared to euthyroid lambs, hypothyroid lambs have an increased susceptibility to death from starvation and hypothermia. Severely affected hypothyroid lambs usually have thin or very limited wool covering. They are weak and are often slow to stand and suck or may completely fail to do so. Walking may be difficult due to abnormalities of the bones of the limbs. Their ability to maintain body temperature is compromised, and they have an increased risk of mortality, particularly if the climatic conditions are unfavourable. Some affected lambs are born dead and many die in the first 24 hours of life. Goitre is usually evident but variable in degree. In some cases, the enlargement of the thyroid gland is extreme, causing a very large swelling in the region of the cranio-ventral throat. The swelling may partly occlude the trachea and cause dyspnoea. Palpably goitrous lambs of an otherwise normal birth weight are typically two to three times more likely to die in the immediate perinatal period than non-goitrous lambs in the same flock.117,118 It has also been observed that lambs with large goitres are more likely to die than those with small goitres (or none).109 The presence of goitre is not, however, an accurate indicator of the state of the thyroid gland or the contemporaneous degree of hypothyroidism when a lamb is born. Nor is the size of the goitre a good indication of the severity of gestational iodine undernutrition in individual cases— an observation reinforced by the fact that twin lambs can have significantly different goitre scores from each other. In some cases, lambs may be born with hypothyroidism and a high risk of neonatal death, but thyroid enlargement

is not obvious and careful palpation is necessary to detect the goitre.119 In some hypothyroid lambs, enlargement of the thyroid may be clinically undetectable and histopathology necessary to detect the hypertrophic changes in the gland structure. The clinician should not rule out hypothyroidism as a contributor to neonatal deaths based on the absence of goitre.105 Histologically severe hypothyroidism and an associated increased risk of neonatal mortality can occur in affected flocks even when most lambs have relatively minor degrees of clinically detectable thyroid enlargement.117 Conversely, congenital goitre may occur in flocks of newborn lambs without an associated increased risk of mortality.120 This may be particularly evident if climatic conditions favour the survival of neonatal lambs. It is probable that the severity of the developmental abnormalities affecting the newborn lamb is related to the timing and the duration, as well as the degree, of iodine undernutrition during gestation. These aspects of the deficiency syndrome play out in unpredictable ways, making it difficult to relate the pattern of goitre development to the likelihood of a lamb’s survival and future health. Whatever the history of the development of the syndrome in individual flocks, it is clear that goitrous lambs which survive for the first few days of life can recover and develop normally if they receive adequate iodine subsequently, either in ewes’ milk or by therapy. The goitres gradually decline in size over a period of a few weeks. There have been several field surveys of sheep flocks conducted to investigate the range in quality of iodine nutrition across regions and across seasons in Australia. In many cases, it has been observed that levels of thyroid hormone in ewes are often low, although goitres in newborn lambs are infrequently reported. Those observations, in addition to observations of hypothyroid deaths with minor or unobservable goitres in other studies, suggest that hypothyroidism may be an under-reported contributor to neonatal lamb deaths in Australian flocks. Clinical hypothyroidism in adult sheep appears to be rare, but subclinical IDD may reduce reproductive performance and wool production. In ewes, iodine deficiency can lead to reduced wool production. Some other effects which could be considered effects on the reproductive performance of ewes—such as a reduction in fertility and fecundity, increased gestation length and reduced lamb birth weights—may in fact be a result of iodine deprivation of the foetus rather than effects on the ewe directly. Iodine supplementation of ewes grazing white clover pasture has led to an improvement in the numbers of lambs born and a small improvement in lamb survival in a Romney flock in New Zealand. Supplemented ewes produced

4. 6 Iodi n e D e f ic i e nc y ( I nc lu di ng G oi t r e a n d Hy p o t h y roi di sm)

1.71 lambs per ewe, while unsupplemented ewes produced 1.57. The effect of supplementation on foetal numbers occurred in the first third of pregnancy, suggesting that iodine supplementation may have enhanced embryo or early foetal survival.121 Supplementation of ewes in an iodine-deficient area of northern Tasmania resulted in a 6% increase in fleece weight of the ewes.122 The response occurred in the absence of any effect on perinatal lamb survival or subsequent lamb growth.

4.6.9  Diagnosis of Iodine Deficiency Congenital hypothyroidism due to IDD can be confidently diagnosed when a high neonatal mortality rate is accompanied by palpable goitres in a significant proportion of the lambs. At necropsy, the presence of enlarged thyroid glands in newborn lambs is a strong indicator of present or recent-past iodine insufficiency, but in cases where the gross enlargement is unconvincing, the gland should be dissected and weighed. In normal newborn lambs weighing 4 to 5 kg, the two thyroid glands together are usually less than 2.0 g (0.8 g/kg BW provides strong evidence that a lamb experienced iodine deprivation in foetal life, and ratios between 0.4 and 0.8 are considered marginally goitrous.123 Thyroid glands can, in some instances, be extremely large (for example, >50 g) and be so large and engorged as to partly occlude the trachea. Histopathology of affected thyroid glands will provide further information about the nature of the thyroid enlargement and the activity of the thyroid gland. Based on the histological appearance, goitres are classified as either of the colloid type or parenchymatous (or hyperplastic) type. Parenchymatous goitre is seen when a lamb is born in a hypothyroid state and the gland is under sustained TSH stimulation. The thyroid follicular cells are enlarged and columnar in shape rather than flattened or cuboidal. There is little colloid within the follicular lumen. These histological changes also occur in hypothyroid lambs in the absence of clinically detectable thyroid enlargement. Consequently, histopathology is important in the diagnosis of subclinical hypothyroidism.124 If the goitre is of the colloid type, the follicular lumen contains much colloid and the follicular cells are in an atrophic phase. Colloid goitre is usually interpreted as an indication of a previous period of hypothyroidism which has

99

resolved, with some of the structural changes still present despite the decline or absence of on-going TSH stimulation. Colloid goitre indicates that there was, in the past, a period of iodine deficiency or other form of interference in thyroid hormone production which was resolved by the time of examination. Serum biochemistry can confirm the presence of hypothyroidism. In normal adult sheep, serum T4 levels usually exceed 45 nmol/L. In hypothyroid lambs, serum I, T4 and T3 levels are very low. Normal newborn lambs born to ewes which have received adequate iodine nutrition will have T4 and T3 concentrations in blood higher than their dams—T4 concentrations >200 nmol/L could be considered normal. Serum T4 levels below 50 nmol/L in neonatal lambs indicate hypothyroidism.

4.6.10  Treatment and Prevention of Deficiency Affected animals can be treated with oral solutions of potassium iodide (KI) (20 mg per lamb) or with parenteral iodised poppy seed oil containing 40% w/v iodine (Lipiodol®). Oral solutions of KI provide shorter protection from deficiency but give a more rapid response. This is the better approach for treatment of neonatal lambs with congenital goitre. In flocks where there is a significant risk of iodine deficiency affecting the viability of newborn lambs, pregnant ewes can be given preventive treatment in mid- and late pregnancy with two oral doses of KI (280 mg) or potassium iodate (KIO3) (360 mg) approximately 1 month apart. Potassium iodide can be dissolved in water (28 g per litre for a 10 mL dose) for oral administration. Solutions should be prepared immediately before use because iodine volatilises readily at ambient temperatures. Treatment should be timed such that most ewes are treated at the beginning of the fourth and fifth month of pregnancy. If the ewes are grazing goitrogenic feeds, treatment at that level may not completely prevent the occurrence of hypothyroidism in lambs but is expected to prevent neonatal mortalities associated with iodine deficiency.120 Alternatively, salt licks containing KIO3 (15 to 25 g per 100 kg of salt) can be provided, but intake of salt licks within a flock is variable and not all ewes will ingest sufficient iodine if other dietary sources are inadequate. KIO3 is the preferred source of iodine in licks because it is more stable than KI, which gradually loses its iodine content over time. A premating injection of ewes with 1 mL of iodised oil will prevent congenital goitre in their lambs for at least one, and possibly two years.122 The nature of the oily injection makes the administration of the product relatively

100

CHAPTER 4: Clinical Aspects of Trace Element and Vitamin Nutrition

slow and difficult, and its use would normally only be considered when the risk of congenital hypothyroidism in lambs is known to be high and the use of oral solutions during pregnancy not feasible. Selenium-containing enzymes (5’-deiodinases) are involved in the conversion of T4 to T3, and a deficiency of

selenium in ewes and their foetal lambs can result in the birth of lambs which have low levels of circulating T3.125,126 The clinical significance of this is not yet clear. The need for preventive treatment is difficult to predict, and a number of trials have failed to detect any response to iodine supplementation, even when there were strong

Box 4.2  A SUMMARY OF THE BRASSICA SPP PLANTS IMPORTANT IN GRAZING ANIMAL NUTRITION, WITH THEIR POTENTIALLY TOXIC METABOLITES FORAGE BRASSICAS AND DUAL-PURPOSE CANOLA

A number of forage brassicas are available in Australia as special-purpose fodder crops for sheep and cattle, either for providing feed in winter when growth of grass–legume pastures is low or for achieving high growth rates in weaned lambs in summer. Available species used for sheep include: Forage rape (Brassica napus) Kale (Brassica oleracea) Swede (Brassica napobrassica) Turnips (Brassica rapa)

Leafy turnip (a hybrid between two Brassica spp) Forage radish (Raphanus spp) Forage radish–Kale cross (Raphano-brassicas) (Radish is not in the Brassica genus but is a member of the Brassicaceae family)

The forage brassicas are relatively inexpensive to establish and grow rapidly after sowing, producing abundant feed within 6 to 16 weeks, depending on the type sown. They provide feed which is highly digestible, high in metabolisable energy (11 to 14 MJ ME per kg DM) and with adequate or moderately high levels of crude protein. In the case of turnips and swedes, grazing animals eat the bulbs in addition to the leaves and stems. A high proportion of the carbohydrates in brassicas is readily fermentable, facilitating rapid and extensive degradation in the rumen with reduced methane emissions compared to those on grass-based pastures. Fibre content of the forage brassicas, however, is generally low. Canola refers to a group of varieties of Brassica napus bred for low erucic acid oilseed. Some canola varieties are suitable for grazing before seeds are harvested for oilseed. These dual-purpose varieties are typically sown in autumn (or earlier) and grazed in early winter before being locked up for flowering and seed production. Brassicas produce several chemical compounds which can lead to animal health problems. These include: PLANT METABOLITE

AGENT RESPONSIBLE FOR DISEASE

DISEASE SYNDROMES

Glucosinolates

Breakdown to isothiocyanates, thiocyanates, thionamides, OZTs, nitriles and other potentially toxic compounds.

Goitre, hypothyroidism Rape blindness Brassica-associated liver disease (BALD)

Primary photosensitising agents

Unknown compounds in forage rape, kale and radish–kale hybrids.

Photosensitisation—‘rape scald’—without liver damage See Chapter 15

S-methyl-cysteine sulfoxide (SMCO)

SMCO produces dimethyl sulphide in the rumen. Levels increase as crop ages.

Small quantities reduce growth rate. Higher doses lead to haemolytic anaemia. See Chapter 20

High levels of free sulphates and sulphur-containing compounds.

High ruminal levels of sulphur and sulphate Reduce the bioavailability of copper and selenium Increase risk of polioencephalomalacia Rape blindness Nitrate converted to nitrite in the rumen Methaemoglobin production, cyanosis and death if severe

Propensity to accumulate high levels of nitrates on high-nitrogen soils Unknown substance

Unknown

Acute pulmonary oedema and emphysema Rape poisoning127

In addition to the specific chemical compounds which may lead to any of the described disease conditions, there are other characteristics of the plants which may lead to disease occurrence. The high levels of rapidly fermented carbohydrates and low levels of fibre may predispose sheep to ruminal acidosis, enterotoxaemia and red gut, particularly if the sheep have previous exposure to the forage (and there is therefore no adjustment to the novelty of the feed) or if their access to the forage is not moderated while the digestive tract adapts to the diet.

4.9 M a ng a n e s e Nu t r i t ion

101

Box 4.3  MANAGEMENT OF GRAZING ON BRASSICA SPP PLANTS TO AVOID THE RISKS OF ANIMAL HEALTH DISORDERS Some steps which can be taken to avoid problems are summarised herein. • Provide supplementary iodine, particularly if pregnant ewes are grazing forage brassicas for more than a few weeks. • Vaccinate against enterotoxaemia. • Do not graze forage rape, kale or radish–kale hybrids before plant maturity, after which time the risk of photosensitisation is reduced. In the case of forage rape, plant maturity is indicated by a purple colour developing in the leaf. • Introduce the forage slowly—provide initial access for 1 to 2 hours per day only, for 1 week, then slowly increase. • Do not allow hungry stock access to the forage. Ensure sheep have had access to sufficient feed in the hours before introduction. This step is particularly important if the sheep have prior experience of the fodder and are likely to commence grazing quickly when introduced.

grounds for suspecting that a deficiency syndrome may occur. Consequently, a decision to provide supplementation to ewes should be based on a thorough analysis of the risk of production losses or lamb mortality in the flock in question and the cost of providing additional iodine. The challenge is made more difficult by the lack of a reliable measure of the iodine nutritional status of sheep. Thyroid hormone concentrations in blood are a poor indicator of the likelihood of responses to supplementation. In regions where iodine deficiency has occurred previously, the provision of Brassica forage crops to pregnant ewes as winter feed should be routinely accompanied by iodine supplementation. A number of precautionary steps should be taken when grazing Brassica spp forages, and these are summarised in Box 4.3.

4.7  IRON NUTRITION Dietary iron deficiency does not occur in grazing ruminants. Grazing animals ingest sufficient iron in natural diets from both plants and soil. Milk is a poor source of iron for lambs, but they obtain iron from accidental ingestion of soil from the dam’s udder. An iron-deficiency anaemia has been reported in lambs raised indoors, in which 2% of the lambs died with anaemia amongst other pathological changes.128 Compared to lambs raised outdoors, the indoor-raised lambs on three farms had, on average, lower haemoglobin concentrations (8.4 to 9.4 cf. 11.7 g/dL) and lower haematocrit levels (28 to 32 cf. 38%).

• Provide additional roughage (fibre). In addition to the provision of hay there are several grazing management strategies which encourage the inclusion of higher fibre plant material (seek expert advice). • Monitor sheep grazing forage brassicas carefully and remove stock promptly if signs of photosensitisation, anaemia or nitrite intoxication occur. The first signs may be reduced grazing activity. • Take particular care if conditions favouring the prior accumulation of soil nitrogen exist. These include the use of nitrogenous fertilisers, previous drought conditions and autumn-sown fodders. Overcast conditions also favour the accumulation of nitrates in brassica plants. • Remove animals from forage brassicas 1 week before sale for slaughter to avoid meat taint.

In contrast to deficiencies of the trace element, excess dietary iron can interfere with copper absorption.

4.8  MOLYBDENUM NUTRITION Molybdenum (Mo) is required for several metalloenzymes in animals but a deficiency syndrome in animals has not been reported. The importance of Mo to the sheep industry in Australia is the widespread problem of low soil levels of Mo affecting pasture growth and the interference with copper metabolism of sheep caused by high dietary levels of Mo. In many cases, molybdenum-induced copper deficiency occurs as a result of Mo being applied to pastures to improve the growth of plants, particularly leguminous plants like clovers (Trifolium spp).

4.9  MANGANESE NUTRITION Manganese is an essential trace element for carbohydrate and lipid metabolism in animals, but there are no reports of deficiency syndromes in naturally grazed sheep. There is one report of bone and joint disorders in lambs fed diets artificially low in manganese.129 In plants, however, both deficiency syndromes and toxicity caused by excess manganese are reported. Manganese toxicity in grazing animals has been reported in Australia, associated with the grazing of lupins (Lupinus albus) which accumulate manganese to high levels.17

102

4.10

CHAPTER 4: CliniCAl ASPECTS oF TRACE ElEmEnT And ViTAmin nuTRiTion

ZINC NUTRITION

Lambs fed artificially zinc-deficient diets have a reduced feed intake as a result of a loss of appetite. Sustained and severe deficiency leads to the development of parakeratotic skin lesions around the eyes, nose, feet and scrotum.130 Wool growth is profoundly affected, and in lambs, wool may be shed.131 The fleece becomes loose and, in one report, is heavily stained with a red–brown pigment.130 In rams, zinc deficiency suppresses sperm production, and testicular weight declines. In pubescent rams, deficiency completely blocks testicular growth—partly through its effect of appetite suppression and partly due to a specific effect which disrupts testicular secretion.132 There is one report of an increase in fertility in Dorset Horn ewes following zinc and manganese supplementation.133 In that instance, the sheep grazed pastures on light sandy loams with calcareous profiles and topsoil pH values of 6.8 to 8.3. There are several sets of environmental conditions which are known to be associated with zinc deficiency in plants, including calcareous soils of high pH.134 There is no other evidence that zinc deficiency causes clinical or subclinical disease in sheep grazing natural pastures in Australia, but there are reports from other countries. Allen et al. (1986)135 identified three therapeutic uses of zinc which could lead to intoxication of sheep with this element. These are the use of zinc against facial eczema, against lupinosis and in the treatment of footrot. They reported the death of 19 of 100 treated weaners, 14 within 24 hours of oral treatment with 3 g of zinc. At necropsy, there was marked necrosis and a lime-green discolouration of the mucosa of the abomasum and duodenum.

4.11 INVESTIGATION OF MICRONUTRIENT DEFICIENCIES Trace element nutrition, particularly dietary deficiencies, can be investigated by the collection of a varying range of tissue and soil samples. The choice of the most appropriate samples depends on the circumstances prompting the investigation and the time of the year it is performed.

4.11.1

Clinical Pathology

Clinical pathology can be used: • When specific clinical signs are evident, such as an outbreak of long bone fractures or myopathy • When ill-thrift is suspected or when sheep (particularly young sheep) fail to grow and produce wool as well as expected

• When carrying out routine monitoring to determine trace element nutritional status of a flock of sheep (this can detect deficiencies which are completely subclinical or which only occur in occasional years)

4.11.1.1 Plant and Soil Testing Testing of plants to predict the availability of trace elements to grazing animals ignores the importance of soil ingestion as a source of nutrients. Ingestion of soil is an important source of cobalt, iodine and, to a lesser extent, selenium.136 More soil is ingested when pastures are short (autumn and winter, and at high stocking densities) than when pastures are longer, such as in spring. Soil is not necessarily a useful source of copper, and some soils may reduce the availability of copper ingested in plant material because of the levels of Fe, S or Mo.137

4.11.1.2 Seasonal Variations in Trace Element Availability As pasture dries off in late spring, a number of nutritional changes occur, and these are summarised in Table 4.3. In general, winter to early spring is a good time for routine monitoring or investigations to determine the probability of occurrence of a significant deficiency of the four trace elements in the left column of Table  4.3. Additional factors, as discussed under the heading for each element, should be borne in mind when planning an investigation.

4.11.1.3 Interpretation of Results ‘Normal’ levels for trace element concentration in animal and plant tissues are published in a number of sources, and it is the usual practice of most laboratories to provide ranges which are considered to reflect adequate levels and those for which responses to supplementation may occur (the marginal range) or are very likely to occur (the deficient range). With all trace element nutrients, the lower the level in the marginal and deficient ranges, the greater the likelihood of a response to supplementation occurring. A set of Table 4.3 Changes in Dietary Nutrients from Spring to Summer NUTRITIONAL ELEMENTS WHICH INCREASE IN AVAILABILITY AFTER SPRING

NUTRITIONAL ELEMENTS WHICH DECLINE IN AVAILABILITY AFTER SPRING

Copper Selenium Cobalt Iodine

Vitamin E Crude protein Digestible energy Phosphorus Sulphur

4.11 I n v e s t ig at ion of M ic ron u t r i e n t D e f ic i e nc i e s

Table 4.4 Normal and Deficient Ranges for Blood Clinical Biochemistry in Sheep NUTRITIONAL ELEMENT

DEFICIENT

MARGINAL ADEQUATE

8

Plasma ceruloplasmin (U/L) 40

Erythrocyte CuSOD (U/g Hb) 12 MJ ME/kg DM), and the energy is derived from fermentable non-starch polysaccharide, in contrast to the high starch content of cereal grains and other legume grains such as peas and faba beans.27 The carbohydrates of lupins are fermented relatively slowly, greatly reducing the risk of lactic acidosis, even if the grain is introduced to the diet at high levels without an introductory period. The fermentation pattern of carbohydrates in lupins is less likely to disturb fibre digestion in the rumen than that of cereal grains. Consequently, supplementation of a low-quality, high-fibre diet with lupins can be very effective because the intake of the base diet is relatively unaffected by the addition of lupins. Lupin grain is also a rich source of protein, and earlier experiments with lupin supplementation led to the suspicion that their high protein content was responsible for the ovulatory response. It is now recognised that the response in ovulation rate to lupin supplementation is a result of the ability of lupins to markedly increase the availability of glucose for intracellular metabolism, even when suddenly introduced to the diet in high quantities.28,29 Experimentally, the infusion of glucose directly into the bloodstream will stimulate an increase in ovulation rate similar to that produced by lupin supplementation29, and the effect of lupins on the number of follicles recruited in the luteal phase of the oestrous cycle is a consequence of increased blood glucose levels and, possibly, the accompanying increase in insulin concentrations.30 In areas where the grain is grown, flushing Merino ewes with lupins has become popular. The ewes typically receive lupin grains at the rate of 500 g per day. Increases in OR occur within seven days of commencing feeding. It is usually recommended that ewe flocks be fed the grain for one week prior to and during the first three weeks of joining. In flocks which respond well, the OR increases by 0.3–0.4 and the percentage of ewes lambing by 10–15 percentage points. Methods for feeding out lupins and the possible occurrence of lupinosis are discussed in Chapters 3 and 18.

118

CHAPTER 5: REPRoduCTion 1: FACToRS AFFECTing FERTiliTy And FECundiTy

Table 5.3 Effect of Flushing on Lambing in Merinos

* **

TIME OF JOINING

TREATMENT

NO. OF EWES LAMBING

INCREASE IN BODY WEIGHT (kg) **

EWES WITH TWINS %

Spring

Flushed* Nil

295 297

3.5 3.0

5 7

Autumn

Flushed* Nil

324 324

3.0 1.0

15 6

Three weeks prior to joining and first three weeks of joining Increase during period of flushing

Despite its frequent use, responses to lupin supplementation are not consistent and may be more likely to occur in situations where ewes are receiving diets which are inadequate in nutrition during joining. Lupin supplementation has been found on one occasion to increase OR but also to increase embryonic loss.31 Table 5.3 shows some effects of flushing on body weight and twinning rate in spring- and autumn-joined Merinos. Note that flushing had a large impact on OR in autumnjoined ewes. As already noted, OR is higher in autumn and more responsive to nutritional manipulation in autumn. Many producers with Merino flocks do not want large increases in the twinning rate and the higher rate of lamb mortality that accompanies multiple births in Merinos. Instead, they seek to utilise some degree of flushing to increase the proportion of ewes which lamb (fertility). Giving additional feed over several weeks to ewes which are in body condition score 3 or less can be expected to raise both body weight and OR.

5.2.4 Effect of Ewe Age on Fertility and Ovulation Rate There are several reasons that ewes over 2  years of age have a higher reproductive performance than young ewes. • OR increases with age, peaking at 5 to 7 years, an effect which increases both fertility and fecundity. • Mature ewes out-compete maiden ewes for the attention of rams at joining. Compared to mature (2½ years or more) ewes, maiden ewes have a shorter oestrus and less overt oestrous behaviour, are less attractive to rams and are mated on fewer occasions during each oestrus. • The maternal ability of ewes increases with age. Compared to older ewes, maiden ewes perform less well at and immediately after lambing—their maternal inexperience, rather than their age, contributes to a generally poorer maternal ability and a lower survival rate of their lambs compared to multiparous ewes.32

5.2.5

Ovulation without Oestrus

Some ovulations in the ewe are not accompanied by oestrus and, therefore, mating will not occur even if a ram is present. Ovulation without oestrus behaviour is called a silent heat. Such ovulations occur at the onset of puberty, at the start and possibly the end of each breeding season and, in the case of Merinos, quite commonly during spring and summer. Silent heats occur when ovulation is not immediately preceded by a period of progesterone priming in the brain. Within the breeding season this priming is reliably supplied by the corpus luteum of the previous oestrous cycle. This luteal progesterone has other important roles, permitting normal functioning of the new corpus luteum and uterine endometrium after the next ovulation. Whereas ovulation without oestrus is quite common, oestrus without ovulation appears to be very unusual.

5.2.6 Failure of Fertilisation Due to Maternal Factors Fertilisation may fail due to faults in the maternal reproductive tract environment. Pasture oestrogens, for example, interfere with sperm transport through the cervix, as discussed further herein. Various controlled breeding techniques (for example, synchronisation of oestrus with progestagen sponges and superovulation of donor ewes for MOETb) also alter cervical function and impair sperm transport. Physical abnormalities of the female genital tract may also influence the likelihood of fertilisation— Quinlivan et al. (1966)33 found some abnormality in 6% of parous 2½-year-old ewes and in 15% of non-parous ewes of the same age group. In naturally cyclic ewes which ovulate more than one ovum, fertilisation is nearly always ‘all or none’. Hence, if a ewe ovulates two ova and is mated, the outcome is usually two zygotes or no zygotes.2 Little is known about possible causes of defective oocytes in ewes under natural conditions, and their occurrence is probably rare.

5.2.7

Management of Ewes at Joining

Within flocks, ewes are sometimes joined in mobs of a single age group or, more commonly, multiparous ewes are joined in mixed-age mobs and the maiden ewes are joined as a separate mob. Maidens tend to be poor competitors with older, more experienced ewes that exhibit a longer and stronger oestrus, and maiden ewes are less active at seeking rams when in oestrus than older ewes. Experience of this in the field varies, and some producers obtain satisfactory or good fertility in the maidens when all ewes b  Multiple ovulation and embryo transfer. MOET programmes are described in Chapter 9.

5.3 A bnor m a l i t i e s a n d D i s e a s e s A f f e c t i ng Ew e Fe r t i l i t y

are joined as a single mob. The risk of reduced fertility of maiden ewes, joined as a single-age group or in a mixedage flock, can be avoided to some extent with higher ramjoining percentages.34 To ensure reasonable fertility, maiden Merinos should have reached a body weight of approximately 80% of their adult weight by the time they are first joined. For mediumwool types of Merino ewes, this represents a body weight of 40–45 kg. Some husbandry procedures can adversely affect reproduction. Ewes may be crutched just prior to joining without any negative effect. Shearing of ewes reduces their attractiveness to rams,35 although the effect gradually declines over the 10-week post-shearing period. The lesser sexual stimulation of rams from shorn ewes may reduce the number of times an oestrous ewe is mated—with consequent negative effects on fertility. It is preferable to organise the farm management calendar so that few, if any, procedures need to be carried out on the ewes or rams during the joining period. Repeated mustering, yarding and handling interfere with ram–ewe contact and may reduce flock mating activity and fertility. Some chemicals employed to control parasites and other diseases, if applied just before or during joining, may interfere with fertilisation or embryo development.

5.3  ABNORMALITIES AND DISEASES AFFECTING EWE FERTILITY 5.3.1  Phyto-Oestrogenic Infertility Phyto-oestrogenic infertility in ewes occurs as a result of the oestrogenic activity of isoflavone metabolites which are found mainly in the laminae of green legumes, particularly some cultivars of subterranean clover (sub-clover) (Trifolium subterraneum) and red clover (T. pratense). The sub-clover cultivars with the highest isoflavone levels are Yarloop, Dwalganup and Dinninup. Medium levels are found in Geraldton and Tallarook. There are two different clinical manifestations of phyto-oestrogenic infertility in ewes. Temporary infertility occurs when ewes graze green oestrogenic clover for a short time, including during the period of mating. Fertility recovers to normal levels within a few weeks of removal from the pasture. Permanent infertility (‘clover disease’) occurs when the ewes graze such pastures for extended periods, leading to irreversible changes in the reproductive tract. The abnormalities induced by the chronic ingestion of phyto-oestrogens are different from those of temporary infertility and are not an extension of the responses occurring during episodes of temporary infertility.36

119

Over the past few decades, the incidence of the most severe forms of this disease has declined markedly, but subclinical permanent infertility probably remains very common. Chronic exposure to phyto-oestrogens also leads to urinary tract problems in wethers, but rams do not appear to be affected.

5.3.1.1  Pathophysiology of Permanent Infertility Two of the ingested isoflavones, formononetin and daidzein, are converted in the rumen to equol. Equol is absorbed, and most of it is conjugated with glucuronic acid in the plasma. The small proportion of unconjugated equol is strongly oestrogenic and is the major active oestrogen responsible for clover infertility.37 The principal lesions causing lower reproductive rates occur in the cervix. These lesions, which present no clinical signs, are the most important abnormalities occurring in subclinical permanent infertility. The superficial epithelium of the cervix of ewes exposed chronically to oestrogenic clovers contains a lower proportion of stratified squamous and mucus cells and a greater proportion of single-layered columnar cells. The changes in the cervix are, in effect, a trans-differentiation of the endocervix so that it resembles endometrium.38 As a consequence of both structural changes and a loss of ability to respond to endogenous oestrogen, the cervical mucus in affected ewes is very watery; it has a decreased spinnbarkheit (visco-elasticity). Without this normal mucus structure, sperm transport through the cervix is greatly impaired39 and the number of sperm reaching the oviducts is greatly reduced. In addition to the cervical changes, chronically affected ewes develop endometrial cysts as a result of cystic hyperplasia of the endometrium. This may be complicated by bacterial endometritis. The endometrial pathology appears to have a lesser effect on conception rates than does the interference with sperm transport.

5.3.1.2 Dystocia Clover-affected ewes often suffer from dystocia. In cloveraffected flocks the incidence can be high and can result in the deaths of 30% to 40% of lambs and 15% to 20% of ewes unless very frequent observations are made and assistance is rendered quickly to ewes with difficulties. The dystocia is apparently due to a failure of the vulva to dilate. The lamb is presented into the vagina, but the ewe is unable to expel the lamb through the vulva. Strong traction, with or without episiotomy, is required to deliver the lamb.40 Septic metritis is a common sequel to dystocia. Without assistance, the lamb is not expelled, and secondary uterine inertia develops.

120

CHAPTER 5: Reproduction 1: Factors Affecting Fertility and Fecundity

5.3.1.3  Lactation in Maiden Ewes and Wethers Maiden ewes and wethers may lactate as a result of prolonged exposure to oestrogenic pasture. The mammary secretion varies from a yellow viscous fluid to apparently normal milk. The degree of teat elongation in wethers has been used as an index of pasture oestrogenicity but may be too sensitive to distinguish differing levels of oestrogenic intake.41

5.3.1.4  Other Effects on Wethers Uroliths containing crystals of equol metabolites can obstruct the urethra, particularly at the urethral process. The squamous metaplasia of the prostate and bulbourethral glands which also occurs in wethers grazing oestrogenic pastures may contribute to the formation of crystals and may encourage obstruction in the pelvic urethra.c

5.3.1.5  Effects on Fertility While the lesions of ‘permanent infertility’ are indeed permanent, the infertility is not complete. Affected ewes can still produce lambs. The effect of the phyto-oestrogens is to reduce the probability of each ewe conceiving under normal mating conditions and hence to reduce the flock’s reproductive capacity. Although the classical ‘clover disease’ is now rarely seen, on properties where it does occur ewe survival rates are reduced by conditions such as hydrops uteri, dystocia and uterine prolapse. With both the severe form and the subclinical form, phyto-oestrogens have a predominant effect on the number of ewes lambing. As the effects accumulate, ewe conception rates progressively decline with age.

of a significant content of oestrogenic cultivars of T. subterraneum in the pastures.

5.3.1.7 Control The long-term solution is pasture renovation in order to replace the oestrogenic cultivars. This is neither easy nor cheap; the cost of the problem must be weighed up against the potential loss of often very productive pastures.42 Short-term control includes the assessment of the risk associated with each pasture on the farm. The young ewes (weaners and hoggets) are grazed on the least oestrogenic pastures during the times of the year when the pastures are green. Dry ewes (never to be mated), wethers and old ewes (with short breeding futures) are grazed on the high-risk pastures. Extension of the joining season by leaving the rams in with the ewes for long periods may increase the lambing percentage and is practised on some affected properties to allow the production of sufficient ewe lambs for future breeding ewe replacements.

5.3.1.8  Temporary Infertility Ewes grazed on green oestrogenic pastures during joining may show reduced conception rates due to temporary clover infertility. The effects of the phyto-oestrogens include a reduction in the incidence of oestrus, interference with ovum transport and a reduction in sperm transport.43 Some experiments have also shown a negative effect on ovulation rate.44 Some of the effects of grazing plant oestrogens may persist for three weeks after removal from the pasture but appear not to persist for longer than four weeks.

5.3.1.6 Diagnosis

5.3.1.9  Coumestans in Medicago spp

Phyto-oestrogenic infertility must be differentiated from other common causes of low marking percentages, particularly low body weight of ewes at joining; infertility of rams, particularly that caused by ovine brucellosis; and high perinatal lamb mortalities from a variety of causes. Pregnancy diagnosis of ewes and examination of the rams will assist the diagnosis. Classical clover disease should be suspected when there are clinical signs in ewes and wethers, a high incidence of dystocia and a history of severely depressed marking rates. Subclinical permanent infertility is more difficult to diagnose because clinical signs are absent and the history is often unremarkable—marking rates may be lowered by only 10% to 20%. Definitive diagnosis will be made on the cervical histopathology of a sample (minimum of 12) of older ewes from the flock and the agronomic identification

Coumestans in lucerne (Medicago sativa) and some other medic species are also oestrogenic, but their effects are always temporary. They reduce ovulation rate during the period that ewes are grazing them, but the effects disappear upon removal. Lucerne often develops high coumestan levels late in its growing season45—typically March onwards.

 See Chapter 19 for a more detailed discussion of this disease in wethers.

c

5.3.2  Embryo Mortality In the absence of phyto-oestrogens or other substances interfering with sperm transport, the vast majority (85% to 95%) of ovulated ova are fertilised when a ewe is mated by a fertile ram.46 Losses of embryos in the subsequent 30 days, however, are relatively high, and embryo mortality is the major cause of loss of lambs between fertilisation and birth. Infectious abortion can cause high losses, but outbreaks are sporadic and infrequent under the extensive grazing conditions common in Australia. By contrast,

121

5.3 A bnor m a l i t i e s a n d D i s e a s e s A f f e c t i ng Ew e Fe r t i l i t y

embryo mortality occurs to a significant level in most or all flocks in most or all years. Estimates of embryo mortality commonly range between 20% and 30%.47 The majority of these losses occur before day 18 post-fertilisation, when implantation is expected to occur33,46, and most of these losses occur between day 4 and day 14.48 The embryo normally passes through the fallopian tube to the uterus on day 4 or day 5 following fertilisation. The embryo’s persistence and survival require the continuing production of progesterone by the corpus luteum. In a ewe with no embryos, PGF2α synthesis in the uterus leads to luteolysis, with the subsequent resumption of follicular development and a return to oestrus. In a ewe with one or more healthy embryos, interferon tau is secreted by the embryonic trophoblast before day 13 and acts as a signalling mechanism preventing the synthesis of PGF2α. This process is the basis of the maternal recognition of pregnancy.49,50 Ewes in which all embryos die before day 13 return to oestrus between days 16–18 (during the normal breeding season) and are therefore not distinguishable in the field from ewes in which fertilisation failed. Ewes which lose all embryos after day 13 have a delayed return to oestrus.51 Ewes that lose one or more embryos but retain one or more embryos can be expected to have a normal pregnancy. The significance of embryo mortality, from the viewpoint of flock productivity, is that the survival of each embryo within a multiple-ovulating ewe is independent of survival of the other embryo(s), so that most embryonic mortalities in multiple-ovulating ewes do not lead to the ewe losing all conceptuses and returning to oestrus. Considering that most multiple conceptions in commercial sheep production are twins, embryonic mortality leads to a reduction in the number of twin-bearing ewes and an increase in the number of single-bearing ewes. By contrast, when there is a failure of fertilisation, this usually means that no ova are fertilised and the ewe will return to oestrus and, provided the rams are still present, have another chance to conceive. In the case of ewes with a single ovulation, there is no difference in the outcome between fertilisation failure and embryonic loss before day 13. In both cases she will return to oestrus. The greatest impact of embryonic mortality is on reducing the number of lambs born to multiple-ovulating ewes. The next most significant effect is increasing the number of ewes which lamb late in the lambing period. The chance of an embryo dying is higher following multiple ovulations than in single ovulations. Estimates vary (summarised and analysed by Geisler et  al. (1977)52), but survival rates of 95% for embryos from a single ovulation, 85% for twin ovulations and 70% for triplet ovulations

Table 5.4  The Reproductive Performance of 2.5-Year-Old Romney Ewes Conceiving to Service at One Oestrus PAROUS EWES

NONPAROUS EWES

NUMBER PERCENTAGE NUMBER PERCENTAGE Ova produced per 100 ewes

136

132

Fertilisation rate 129

94%

116

85%

Survival to 18 days postfertilisation

104

76%

97

71%

Survival to 30 days

97

71%

92

68%

Survival to 140 days

95

70%

86

64%

Source: Adapted from Quinlivan et al. 1966.33 Note: Roughly half of the ewes were parous in the previous year and half were nonparous, indicating that embryonic mortalities account for around 20% of fertilised ova.

have been proposed. These estimates seem high, given the data of Quinlivan et al. (1966)33 (Table 5.4), and lower survival rates (75% to 90% for twin ovulations) have been found in an Australian study with Merino sheep.53 Three factors—the relatively high rate of embryonic mortality, its randomness (usually affecting only one of twins) and its higher frequency in multiple pregnancies than in single pregnancies—combine to make embryonic mortality a significant obstacle to greater reproductive efficiency in sheep. Embryo loss in some flocks or flocks in some geographical regions may be associated with delayed returns to oestrus (or apparent failure to return to oestrus, depending on the length of the joining period). This is seen most clearly in the few cases of selenium deficiency which have been associated with ewe infertility in Australia (see Chapter 4).

5.3.2.1 Aetiology The reasons for most embryo losses in commercial flocks are unknown. Some losses are attributable to intrinsic faults within the embryo, and hence their loss is desirable (rather than the subsequent abortion or birth of abnormal foetuses). While some embryo loss results from the fertilisation of ova by heat-damaged spermatozoa, in vitro culture and in vivo embryo transfer studies suggest that most losses are due to failures in the uterine environment. Faulty nutrition, abnormal temperatures, endocrine imbalances and asynchronous development of the embryo and endometrium have all been suggested as causes. Deficiencies of zinc, iodine and selenium have occasionally been implicated (see Chapter 4).

122

CHAPTER 5: Reproduction 1: Factors Affecting Fertility and Fecundity

Undernutrition during the period immediately following mating has been occasionally associated with increased embryonic mortality, but the level of undernutrition must be severe and the duration prolonged (at least three weeks) before the effect is significant. The severity of the undernutrition required to cause embryonic mortality is much greater than that which would occur with normal standards of sheep husbandry.47 The effect may be greater in young ewes than in mature ewes and in ewes with multiple embryos rather than singles.46 Sustained high environmental temperatures, particularly around the time of mating, may increase the incidence of both fertilisation failure and embryonic mortality. In a Western Australian study with Merino ewes, a negative association was found between the number of lambs born, the number of days over 32.5 °C during the mating period and the mean daily maximum in the three weeks after mating, an effect considered to occur due to increased embryonic mortality.54 Experimentally, the effect of increased temperatures has been inconsistent, but one factor which appears to reduce the impact of high daytime temperatures is diurnal variation in temperature—mimicking the effect of cool nights between hot days.46,47

5.3.2.2  The Relative Importance of Embryo Mortality In individual flocks experiencing an infertility problem, the relative importance of failure to mate, failure of fertilisation and embryo mortality varies. Normally, with return rates of 20–30%, fewer than a third of returns are due to failure of fertilisation. The presence of pasture oestrogens or some controlled breeding procedures will increase the risk of fertilisation failure, but, provided mating with fertile rams occurs, embryo loss is usually more important than failure of fertilisation. Failure to mate is the least common of these three causes of failures to conceive and generally only happens with out-of-season joinings (when ewes fail to cycle) or the joining of ewes to a single, incapacitated ram.

5.4  FACTORS AFFECTING THE FERTILITY OF RAMS USED FOR NATURAL JOINING 5.4.1  Photoperiodicity in the Ram Rams of all breeds show a seasonal variation in testicular size that is influenced by photoperiod and mediated through seasonal changes in gonadotrophin secretion, but the magnitude of the variation within a year varies markedly between breeds. Breeds developed in high latitudes (more northerly breeds in the northern hemisphere) have a short and sharply defined breeding season in ewes and

a marked variation in testicular size, testosterone levels, libido and sexual activity in rams. These breeds, such as the Herdwick, Wiltshire and Scottish Blackface, behave similarly to wild sheep (the Mouflon) and feral sheep (the Soay), with a peak in testicular size in September–October in the northern hemisphere. Breeds developed in more southerly latitudes of the northern hemisphere, such as the Merino, have a smaller variation in testicular size and peak about one month earlier than the northern breeds.55 Portland sheep (now a rare breed), Dorset Horn sheep (derived from the Portland breed) and the Poll Dorset56 (derived from the Dorset Horn) show characteristics similar to those of the Merino in this regard. The trait was first recorded in Portland sheep in the 18th century,57 possibly reflecting the introduction of sheep of Mediterranean origin in their very early development in southern Britain, although the evidence for that is not strong. In Australia, the strong seasonal effect on testicular size has been observed in Border Leicester, Suffolk and Romney rams. When the effects of seasonal variation in nutrition are removed, Suffolk rams show an increase in scrotal circumference starting in late spring (November), peaking in early autumn (March) and then declining through late autumn, winter and early spring. The magnitude of the variation in adult rams is of the order of 31 cm (minimum) to 37 cm (maximum). By contrast, scrotal circumference in Merino rams peaks about one month earlier than in Suffolk rams, starts to increase two to three months earlier and shows a smaller seasonal variation—from 34  cm to 37 cm.58 Romney rams show a variation similar to that of Suffolk sheep, with testicular volume doubling between a low value in November and a seasonal maximum in May.59 While testicular volume, libido, sexual interest in ewes and sperm concentration in semen all decline to some extent in all breeds during winter and early spring, rams do remain fertile and able to mate at any time of the year. The manner in which photoperiod controls or influences the seasonal variation is unclear. The key difference between breeds developed in regions of the world differing in latitude may in fact be the degree to which photoperiod effects are overridden by other stimuli, such as changes in nutrition or, possibly, an endogenous sexual cycle which is influenced, but not controlled, by changes in day length. Even in breeds like the Soay—which has existed in northern Britain for centuries and is genetically close to its wild sheep ancestors—the increase in gonadotrophin secretion commences before the summer solstice, while day length is still increasing. It appears that the hypothalamic response to increasing day length during late winter and spring is to cause a delay in the onset of the breeding season, rather than to prevent it altogether, and eventually the pineal

5.4 Fac t or s A f f e c t i ng t h e Fe r t i l i t y of R a m s Us e d f or Nat u r a l Joi n i ng

gland becomes refractory to the increasing day length and responds instead to the improved nutritional conditions of spring. Rams of breeds with less circumscribed breeding seasons respond differently, in that the delaying effect of the increasing day length is weaker and more easily overridden by other stimuli, such as nutrition. The difference between breeds is likely to be related to the way the hypothalamus interprets and responds to the melatonin signal produced by the changing day length.55,60 Nutrition also influences testicular mass, so the two factors (season and nutrition) combine to affect testicular size. In breeds like the Suffolk, where the seasonal variation in testicular size is large, nutritional effects are weak and testis mass will increase in summer even if the liveweight of the ram is declining due to poor nutrition. In the Merino, by contrast, the influence of nutrition on testis mass is stronger and will override the effect of photoperiod and season.61 The negative consequence of this under Australian conditions is that, without supplementation, the testes of Merino rams grazing dry summer–autumn pastures will decline significantly in size—despite the effect of decreasing day length—at exactly the time when joining occurs and large testes and active spermatogenesis are required.62 The positive consequence is that the testes of Merino rams will increase markedly in size if the rams are grazed on, or supplemented with, a high-energy, high-protein diet over summer in the period leading up to joining. Both the nutritional response63 and the photoperiod response in testicular growth are mediated by the frequency of luteinising hormone pulses.

123

in the previous spring, the ram lambs undergo puberty in their first summer, aged about 5 months, and continue sexual development through the autumn and early winter. Reflecting the breed susceptibility to photoperiod effects, further sexual development is suppressed by increasing day length after the winter solstice and the associated negative effect on melatonin secretion. For some young BL rams, but not all, that sexual immaturity persists into October and, if joined to ewes in spring, they either fail to mate any ewes or only start to mate some weeks after they were introduced. The reasons for the variability between rams are not well understood but may be a consequence of neuro-endocrine or social effects in their earlier development. Nutrition is not considered an important factor.65 5.4.1.1.1  Treatment of Young BL Rams with Melatonin The administration of melatonin implants (Regulin®) to young BL rams in spring before mating stimulates the development of sexual maturity and testicular size, increases testosterone levels and improves semen quality. Experimentally, doses of melatonin of 36 mg or 54 mg (two or three Regulin® implants) early in spring increase plasma testosterone concentrations and scrotal size and may mitigate the risk of poor conception rates when joining groups of maiden BL rams to Merino ewes in spring.66 The work remains experimental only and further studies are necessary to demonstrate the value of melatonin in rams under commercial field conditions.

5.4.1.1  Using Border Leicester Rams for Spring Matings

5.4.2  Body Weight, Nutrition and Fertility in the Ram 5.4.2.1  Testicular Mass and Daily Sperm Production

Border Leicester rams are commonly used in Australia to mate to Merino ewes to produce Border Leicester × Merino (BL-Mo) crossbred progeny, the females of which are referred to as first-cross ewes. These ewes are hardy and moderately prolific and are usually mated to terminal sires to produce second-cross prime lambs. The Border Leicester rams are often mated to Merino ewes in spring (October–November) in order to produce the crossbred progeny in autumn, giving them a good opportunity to be well grown and readily marketable to prime lamb producers in the spring. The libido and testicular size of Border Leicester (BL) rams is low in spring, but mature rams generally mate satisfactorily. The results from using maiden BL rams in spring, however, is highly variable, and sometimes they fail to produce significant numbers of progeny.64 The occasional poor result from using young rams is a consequence of their age and lack of sexual maturity. Having been born

For mature rams in good health, the larger the testes, the greater the number of sperm produced per day (Figure 5.2). A ram with 400 g of testes produces about 6000 × 106 sperm per day, and every additional 100 g of testicular tissue adds around 2000 × 106 sperm to the daily production.67 Notwithstanding the photoperiod effects and breed differences described earlier, it is in general true that testicular mass responds to changes in nutrition. Increases in body condition score through an increased level of feeding result in increases in the size of the testes. The response in sperm production is not, however, immediately measurable in the ejaculates. There is a relatively invariable 49-day period between the initiation of spermatogenesis in the testicular tubules and the appearance of the resultant mature spermatozoa in the distal epididymis. During a six-week joining period, therefore, the spermatozoa that are produced in ejaculates result from spermatogenesis that commenced in the period from seven weeks pre-joining to one week

124

CHAPTER 5: Reproduction 1: Factors Affecting Fertility and Fecundity

Figure 5.2  The relationship between testicular mass (g) and the daily sperm output from the urogenital tract (× 106) is linear over the range 350 g to 700 g, with a slope of 20 and a correlation coefficient of 0.83. Source: Kym A Abbott. Based on data from Lino (1972)67 and Foster et al. (1989)68.

Figure 5.3  There is a strong relationship between scrotal circumference and the mass of the two testes. Source: Kym A Abbott. Blue line—based on data from a study of 110 Merino rams by Foster et al. (1989)68; red line—based on data from a study of 10 fine-wool Merino rams by Lino (1972).67

pre-joining. The condition score and the testicular mass in the two-month period before joining commences are critical in determining the daily sperm output of a ram during joining once epididymal reserves are expended—usually in the first few days, depending on mating load. A condition score of 3–4 for rams at the commencement of joining is recommended. At that condition score, Merino rams are expected to have at least 400 g or 400 mL of testes and, for mature rams in that condition score, it should be significantly more. (It is assumed that 1 mL of testicular tissue has a mass of 1 g.) Excessive feeding resulting in obesity may reduce libido, whereas inadequate nutrition reduces testis size, libido and semen volume.

5.4.2.2  Estimates of Testicular Volume The testicular volume of rams can be estimated by physical examination of the scrotum and scrotal contents. There is a strong relationship between the circumference of the paired testes, as measured within the scrotum, and testicular mass. Foster et al. (1989)68 compared the testicular mass and scrotal circumference (SC) of 110 normal Merino rams and found a linear relationship (total testicular mass (g) = 31.4 × SC (cm) − 564). The measurement of scrotal circumference was highly predictive of testicular mass (r = 0.92). The results of that study, and one by Lino (1972)67 with 10 Merino rams, are summarised in Figure 5.3. From the two studies, one can predict that Merino

5.4 Fac t or s A f f e c t i ng t h e Fe r t i l i t y of R a m s Us e d f or Nat u r a l Joi n i ng

rams with a scrotal circumference of 32 cm will have testes of around 400 to 440 g and that every additional cm adds 23 to 31 g to the testes mass. Purpose-made scrotal measuring tapes are recommended for measuring the scrotal circumference. Selftensioning tapes, such as the Reliabull tape, ensure that a consistent tension is applied to the scrotal circumference of every ram. The circumference is measured by holding the two testes in the bottom of the scrotum with one hand around the neck of the scrotum. The tape is placed around the scrotum at its widest point and the circumference in centimetres is recorded. The ram can be examined while standing

125

with the operator squatting behind, or with the ram sitting and restrained by a second person, and the operator squatting between his hind limbs (Figure 5.4).

5.4.2.3  Sperm Production during Natural Joining In rams that are not joined and are not ejaculating frequently—as they would do if joined to oestrous ewes— spermatozoa accumulate in the tail of the epididymis, vas deferens and ampulla, effectively creating a reservoir of sperm. This reservoir allows rams to include very large numbers of sperm in ejaculates for the first few days of joining. Rams under natural mating conditions may encounter four to six oestrous ewes per day for the first 17 days of joining and are capable of 10 to 20 ejaculates per day. The ejaculates produced on the first day of joining may each contain 2000 to 4000 × 106 spermatozoa. After two to three days of frequent ejaculations, sperm numbers per ejaculate fall dramatically (typically by 90%) and the daily sperm output in ejaculates remains at the lower level—effectively matching daily sperm production—until later in the joining period when the number of ewes in oestrus each day declines (Figure 5.5).69,70,71

5.4.2.4  Spermatozoa Numbers Required to Ensure High Conception Rates from Natural Service

Figure 5.4  The scrotal circumference is measured with a scrotal measuring tape placed around the scrotum over the two testes, while the testes are held in the scrotum with one hand. Source: Kym A Abbott.

The numbers of spermatozoa required for satisfactory conception rates are best known for artificial insemination. Salamon (1962)72 concluded that 120 to 125 × 106 were necessary for AI with extended fresh semen. For good fertility with natural service, the number of sperm can only be estimated, and it is widely considered that 120 × 106 sperm are adequate.

Figure 5.5  The number of sperm per ejaculate declines markedly after the first 16 to 24 ejaculates in the first two or three days of joining and then recovers later in the joining period when fewer ewes are in oestrus each day. Source: Kym A Abbott. Based on data from Raadsma and Edey (1985).70

126

CHAPTER 5: Reproduction 1: Factors Affecting Fertility and Fecundity

Figure 5.6  Under natural mating conditions, the proportion of ewes becoming pregnant and the proportion of pregnant ewes with multiple embryos are higher if the ewes are served two or three times, compared to once. Source: Kym A Abbott. Based on data from Mattner and Braden (1967).69

5.4.2.5  Mating Behaviour and Flock Fertility Ewes are more likely to conceive if served more than once while in oestrus69 (Figure  5.6), and generally ewes are served two, three or more times by one or more rams when joined to multiple-sire groups. Under single-sire mating conditions (where a ram has no competition for access to ewes), rams can be expected to serve three, four or five ewes per day and possibly more.71,73 They do, however, show preference for some ewes over others, so some ewes may be served repeatedly while some, apparently less attractive, ewes are served less often or not at all.74 Under conditions of multiple-sire joining, rams demonstrate less preferential behaviour and, compared to single-sire mating at equivalent ewe:ram ratios, a higher proportion of the ewes are served in multiple-sire joining groups, although interaction between rams leads to a reduction in the average number of services per ewe.73,74,75 There is considerable variation between rams in the maximum number of times each day that they will mount and successfully serve ewes. The number is sufficiently high for most rams (10–20, for example69,69,71) to ensure that, if four or five oestrous ewes are presented in one day, each ewe can be served at least once and, usually, multiple times. From a mathematical point of view, a healthy, fit, libidinous ram which was producing 6000 × 106 sperm per day in the weeks immediately leading up to joining will be able to sustain 12 to 18 ejaculates per day for the first three weeks of joining, each ejaculate containing over 120 × 106 sperm, and thereby inseminate six ewes, each on two or three occasions, during the hours they are in oestrus. If there is no significant synchronisation of oestrus occurring, it can

be expected that, in a flock of 100 ewes, five or six will be in oestrus each day for the first 17 days of joining. In the field, this conclusion is largely found to be reliable, even given the fact that there is wide variation between rams in terms of their libido, behaviour and fitness and, in group-mating systems, in the interactions and dominance behaviour between rams. This means that, unless other factors (as discussed later) are in effect, it is possible to join rams at the rate of one per 100 ewes and expect good rates of conception.76

5.4.3  Puberty and Age Effects in Rams Merino ram lambs reach puberty and become capable of mounting and impregnating a ewe when aged between 125 and 200 days. Ram lambs which are well nourished and grow quickly reach puberty at ages in the lower part of the age range. Puberty in rams is associated with the appearance of spermatozoa in semen and the loss of adhesions between the penis and prepuce, permitting intromission. Sexual maturity therefore is indicated by a freely moveable penis within the prepuce and growth and firmness of the testes.77 The development of libido—demonstrated by mounting behaviour, masturbation and the secretion of androgens—precedes the appearance of spermatozoa.78 Rams of other breeds tend to reach puberty at younger ages than Merinos, an effect which may be related to the natural prolificacy of the breed, as indicated by the relatively high ovulation rate of females.79 To avoid unplanned pregnancies, ram lambs should be weaned and removed from access to their dams and other ewes before 5 months of age in the case of Merinos80 and, to be safe, by 4 months of age in other breeds.

127

5.4 Fac t or s A f f e c t i ng t h e Fe r t i l i t y of R a m s Us e d f or Nat u r a l Joi n i ng

By 12 months of age young rams can produce ejaculates containing a high concentration of highly motile spermatozoa. Rams are usually used for the first time for natural flock matings at 1½ years of age but can be successfully joined to small flocks of ewes at younger ages, such as 7 months of age, if well grown.

5.4.4 The Age Structure of the Ram Flock Rams can remain in the breeding flock to extended ages provided they remain active without lameness, are capable of maintaining good body condition and, therefore, good testicular volumes, and are otherwise sound for breeding. Generally, however, their physical health deteriorates by the time they are 4 or 5 years of age, having been used for three or four breeding seasons. Producers therefore often anticipate replacement of one-quarter to one-third of the ram flock annually. Commercial flock owners usually buy rams from specialist ram-breeding flocks or studs, which are expected to be improving genetically each year. Consequently, a 1½-year-old flock ram purchased from a ram-breeding flock is expected to be genetically superior to a flock ram purchased from the same flock four years previously. There is evidence that the value of the annual genetic improvement may be of the order of $0.50 to $1 per ewe progeny per year.81 The difference in genetic merit between the progeny of young rams and the progeny of older rams will rarely justify the decision to purchase replacement rams at younger ages on genetic grounds alone. An illustration follows in Table 5.5. Table 5.5 shows that the maintenance of a ram team of 100 rams of four age groups requires the annual purchase of 29 rams, but if only three age groups are maintained, it is necessary to purchase 37 rams annually. The younger ram team can be expected to produce progeny of a higher productive value (higher fleece value, for example, in the case of Merino sheep), but if the improvement in value each year is only $0.75 per ewe progeny, the difference in the total annual productivity of the ewes sired by the threeage-group and four-age-group ram teams is only $1281. That difference in value will rarely justify the purchase of an additional eight flock rams, although, for commercial flocks which breed their own ram replacements, the additional return may contribute to the financial justification of the self-replacement strategy. Calculations like this can be performed under a range of conditions, including the depreciation rate of rams (the difference between their purchase price and sale value at end of breeding life), the number of progeny likely to be born from each ram each year and the extent to which their

Table 5.5 The Approximate Age Structure of a Ram Team of 100 Rams in a Commercial Flock Varies with the Age at Which All Rams Are Culled NUMBER OF AGE GROUPS OF RAMS 2

3

4

Number of 1½-year-old rams

53

37

29

Number of 2½-year-old rams

47

33

26

30

24

Number of 3½-year-old rams Number of 4½-year-old rams Difference in total annual productive value of progeny

21 $2638

$1281

0

Note: The example shown is for flocks in which rams are sold after two, three or four years in the breeding flock, where each year’s purchase of rams is genetically superior to those of the previous year. Using the four-agegroup model as a base, the extra productive value of the ewe progeny in flocks with earlier ram-culling practices can be compared to the cost of the extra rams purchased to maintain a younger ram team. Note the following assumptions: Ram team of 100; 10% of rams die or are culled annually. The value of the productivity of the ewe progeny improves by $0.75 each year. Each ram produces 40 ewe progeny per year.

productive value might remain in the flock (the number of progeny retained as breeders or for repeated shearing, and to what age). It is likely that, under most circumstances, the genetic difference between a cast-for-age ram and a young ram is likely to be only a minor contributing factor to a decision to sell old rams after three or four years of breeding.

5.4.5 Husbandry Procedures and Ram Fertility To ensure rams are in good condition with high sperm output when joining starts, extra attention should be given to their management, health and nutrition, beginning 10–12 weeks earlier. Keeping rams in good general health and free of infectious disease is an important component of reproductive management and one of the easiest to accomplish. The ram team is a numerically small component of the sheep flock, so, compared with the cost of managing the whole flock, it is relatively inexpensive to provide them with excellent nutrition and health care. Major husbandry events (shearing, crutching) should be avoided in the eight weeks before joining. Some producers choose to shear Merino rams every six months, but the pre-joining shearing should be planned such that they are carrying three to four months’ of wool growth when introduced to the ewes. Heat stress decreases semen quality. This occurs commonly in rams housed in sheds where ventilation

128

CHAPTER 5: Reproduction 1: Factors Affecting Fertility and Fecundity

and temperature control are inadequate. Under paddock conditions, heat stress is uncommon in Merinos but more common in British breeds. The difference is explained in part by the more pendulous nature of the Merino’s scrotum, although Merino rams with heavy skin wrinkle have a relatively poor ability to control testicular temperature. Because of the strong relationship between condition score, testicular volume and, consequently, the number of spermatozoa produced in the seven-week period before joining commences, steps should be taken to ensure that rams are in good condition before seven weeks pre-joining and are maintained in good condition (score 3–4) until joining. Lupin supplementation can be used to increase ram condition score, testicular volume and fertilising ability leading up to joining. A supplement fed at the rate of 500 g lupin grain per day for 8–10 weeks can increase testicular volume in Merinos from around 400 mL to about 600 mL.82 Cereal grains can be used instead of lupins, but more care must then be taken to avoid grain poisoning. Supplementation of rams to increase testicular mass may enable the use of fewer rams at joining, and the saving which arises from purchasing fewer rams is usually much greater than the cost of the supplement.

5.4.6  Management of Rams at Joining 5.4.6.1  Veterinary Inspection Pre-Joining Inspection of a team of rams before mating involves an assessment of both their genital and general health. It is important to consider the general physical condition of the rams, their age, their condition score and the soundness of their feet and limbs because these factors have a bearing on the ability of the rams to remain active and sexually interested throughout the mating period. Protection by vaccination against clostridial wound infection should be encouraged; the timing of husbandry procedures which might temporarily reduce fertility should be discussed with the owner. As joining usually occurs during periods when there is a risk of flystrike, rams should be treated with protective insecticides to ensure that any wounds, such as fighting wounds, do not become flystruck. Ram examination is best carried out 10–12 weeks before joining is due to commence. This allows time to feed rams to ensure that their condition score and testes volume are optimal for joining and, if necessary, to buy in and acclimatise additional rams if it is found that there are too few fit and healthy rams in the ram team. Inspection of rams is generally confined to physical inspection of body condition and feet and palpation of the external reproductive organs. More involved techniques, like semen collection and evaluation and serving capacity tests,83,84 may have a place when single-sire mating

groups are employed (usually only in ram-breeding flocks) or when investigating specific failures of conception. The routine collection of semen is not warranted, both because of the cost of the procedure and because there is not a clear relationship between measured parameters in the ejaculate and the level of ram fertility—although infertile rams can generally be identified. Palpation of the scrotal contents should include: • Measurement of scrotal circumference, as an indirect measurement of testicular volume. • Estimation of the firmness and resilience of the epididymal tails and testes.85 • Examination of the head and body of the epididymis to detect any abnormalities. • Palpation of the spermatic cords and inguinal regions to detect hernias, abscesses or varicocoeles. • Examination of the scrotum itself, particularly noting the presence of scrotal mange. • Examination of the penis by palpation within the prepuce, although it may also be desirable in some cases to exteriorise the penis and examine the penis and everted prepuce for evidence of injury or infection. Serving capacity tests conducted in pens, under observation, have been used in an attempt to predict the capacity of rams to serve frequently in the field. While rams do vary in their breeding capacity, the ability of pen tests to accurately predict their field performance is only moderate. Some rams which perform poorly in pen tests—possibly as a result of inhibition by the pen environment or by the presence of other rams—do perform satisfactorily in the field.86 The tests are no longer commonly used under commercial conditions.

5.4.6.2  Allocation of Rams to Syndicates Based on Testicular Size As described earlier, larger testes allow greater production, storage and ejaculation of sperm. Large testicular size is an evolutionary adaptation to increase mating success of rams because of the promiscuity of ewes—it is usual for ewes to be mated by more than one ram in any oestrous period when multiple rams are available. In natural mating, and where there is intense competition for ewes (high joining percentage or relatively few ewes), social and physical dominance are the important determinants of mating success—the biggest, strongest, most dominant rams prevent lesser rams from mating oestrous ewes. At low joining percentages or where the ewe flock is large, dominant rams are less able to monopolise all the

5.4 Fac t or s A f f e c t i ng t h e Fe r t i l i t y of R a m s Us e d f or Nat u r a l Joi n i ng

oestrous ewes, and smaller, subordinate rams have a better chance of mating. In these circumstances, in which multiple rams are mating each ewe, larger testes and greater sperm numbers in each ejaculate provide a competitive advantage because the more numerous sperm from the larger testes will outnumber the sperm produced by a competitive ram with smaller testes.87 While natural selection has led to increased testis size to favour rams where multiple sires are mating ewes, in farming systems controlled by non-natural means, increased testis size allows flock managers to reduce competition for ewes by lowering joining percentages, while still ensuring that sufficient sperm are deposited in the reproductive tract of every oestrous ewe. Producers therefore have a choice. They may ignore testis size and join rams at a relatively high percentage (2% or more). Provided they are fertile, the biggest, most dominant rams will sire the most offspring. If the biggest, strongest rams are of low fertility, however, the conception rates may not be as high as could be achieved with highly fertile rams because the low fertility, dominant rams monopolise the mating opportunities. (One study showed that flock fertility falls if completely infertile rams are dominant to fertile rams. In addition to a higher percentage of nonpregnant ewes, more ewes will conceive later in the joining period, increasing the spread of lambing.88) Alternatively, producers may choose to select rams for joining on the basis of large testicular size, and to reduce the joining percentage accordingly. Social and physical dominance becomes less important because (a) All rams used, including the dominant ram, are known to have large testes and therefore expected to have good fertility. (b) The subordinate rams will share in the mating more equally, and they, too, will be known to have good testis size. Knowing that all rams used have large testis volume therefore obviates two problems. First, if relatively few rams are responsible for most of the matings, conception rates should still be satisfactory. Second, the lower joining percentage will reduce the effect of dominance behaviour, and all rams should therefore be represented as sires of the offspring. Lower joining percentages also reduce the number of rams which need to be purchased and maintained. Flock managers can then either spend less on ram purchases by buying fewer rams or spend a similar amount by purchasing better, more expensive rams, or they can make use of a combination of both strategies.

129

5.4.6.3  Duration of Joining In practice, management decisions about the joining ratio and duration of joining are considered together, since they are somewhat interrelated. It is not easy to determine in advance based on a particular property the minimal number of rams and minimum length of joining period which will result in good flock fertility. When joining occurs during the natural breeding season, ewes should be cycling regularly when the rams are introduced, so five weeks is usually adequate. Most ewes become pregnant in the first 17 days, and those that do not should return to oestrus in the second 17-day period. For out-of-season joinings, where most or all the ewes are in anoestrus at the commencement of joining, few ewes have overt, fertile oestrus in the first two weeks, so a joining period of seven weeks is necessary to allow two cycles after mating begins in earnest. Alternatively, teasers (testosteronetreated wethers or vasectomised rams) can be introduced for 14 days (exploiting the ram effect) before the fertile rams in order to increase the probability that all ewes are cycling. When joining extends longer than five weeks (in the breeding season) or longer than seven weeks (out of season) the few ewes that fail to conceive in the first two cycles have a third opportunity. Usually, this is a small percentage of the ewe flock (400 mL (scrotal circumference >32 cm) are able to cover ewes adequately at a ratio of 1% rams to ewes. There are several circumstances where 1% may be insufficient. Examples of such circumstances are listed here: • The rams are in poor condition with low testis volume, or they are excessively obese. • The ram syndicate contains a high proportion of 1½-year-old or very old rams. • The joining period is less than five weeks. • The ewes are maidens or lambs. A joining ratio of 2% is recommended for ewe lambs. • Joining occurs during spring and summer, especially if (highly seasonal) British-breed rams are used. • Joining takes place in rough and scrubby terrain and/ or at very low stocking densities. • Flocks are very small and the use of one or two rams only may involve excessive risk that the poor performance of one ram severely compromises the flock fertility. To manage this risk, it is commonly advised to join rams at 1% plus 1—in this way, small joining groups have a higher ram:ewe ratio than larger groups. For example, using this formula, a flock of 100 ewes would be joined to two rams while a flock of 400 ewes would be joined to five rams. • Some degree of oestrus synchronisation occurs as a result of the ram effect or the use of controlled breeding techniques. Following the successful use of the ram effect with teasers for a spring–summer joining, it is possible that a high proportion of the ewe flock is in oestrus at some time between 18 and 25 days after the introduction of teasers (see Chapter 9) or for 4 to 11 days after the fertile rams are introduced. To achieve good conception rates at that first oestrus, it may be necessary to join the ewes to as many as 4% of rams. Joining ratios should be increased above 1% when one or more of these circumstances is present. In practice, many producers simply run 2% of rams with their ewe flocks as a blanket rule. If some of the circumstances listed earlier do not apply, this policy could be quite wasteful. Active rams lose condition during joining, especially during the first three weeks (the first oestrous cycle of the ewes) as a consequence of reduced time spent grazing. Testicular volume and scrotal circumference decrease markedly during joining.70 The same rams should not be

used for successive joinings with substantial numbers of cycling ewes unless they are given a rest period of six to eight weeks with adequate nutrition between the end of one joining period and the commencement of the next.

5.4.6.6  Using Ram Harnesses to Measure Mating Activity Regular observation of the flock during joining will provide useful insight into the level of mating activity. If considered necessary, however, better estimates of both flock breeding activity and fertility can be obtained by the careful use of ram harnesses and crayons during joining. The procedure recommended is usually as follows: Harnesses are applied to the rams, and services are recorded during the first 18 days of joining. To do this, the ewes are yarded at least once, preferably twice, per week, and the number of marked ewes is recorded. The flock should be inspected daily for lost harnesses and crayons. The crayon colour is changed on day 19 for the rest of the joining period, and observations continue. If joining is in spring, it is better to change the crayon colour only after the first 28 days of joining. For autumn joinings, the proportion of ewes marked in the first 18 days measures mating activity. Flock fertility is assessed from this proportion and the proportion of marked ewes which are re-marked after the first 18 days. Note that a source of error here is that ewes marked with the first colour on day 18 may still be in oestrus on day 19 and may be marked with the second colour. The interpretation of flock crayon data is most straightforward for autumn joinings. When ewes are joined out of season, the failure of some ewes to be re-marked may denote a return to anoestrus rather than a conception. The data obtained with crayons have other uses. For example, the flock can be subsequently divided into early-lambing and late-lambing or dry groups. It should be remembered, however, that the procedure outlined is laborious and hence costly, and it may significantly interfere with joining performance. Apart from the mustering and yarding involved, harnesses can sometimes cause discomfort, wounds and lameness in the rams.

5.4.7  Failure of Fertilisation Due to an Inadequate Number of Rams When adequate numbers of rams are employed, it is expected that 95% to 100% of ova will be fertilised and, after some embryo losses, 80% to 85% of the ewes with fertilised ova will conceive. If the joining ratio is very low, conception rates will decline below this level. Table  5.6 shows the percentages of ewes in a flock expected to lamb following joinings of one, two or three cycle lengths. A conception rate of 70% (percentage of ewes lambing to one

5.5 A bnor m a l i t i e s a n d D i s e a s e s A f f e c t i ng R a m Fe r t i l i t y

Table 5.6 The Effect of Decreasing Ram Power and the Consequent Decrease in Conception Rate for Each Cycle PERCENT CONCEPTION IN EACH CYCLE

PERCENT OF EWES LAMBING 1 CYCLE

2 CYCLES

3 CYCLES

70 60 50

70 60 50

91 84 75

97 94 88

oestrus) is considered satisfactory for Merinos. As conception rate decreases with diminishing ram percentages, so too does the percentage of ewes lambing, but the effect of conception rate on the percentage lambing can be moderated by increasing the length of the joining period. Most of the reduction in conception rate is due to oestrous ewes not being mated at all, but some of the reduction may be associated with failure of fertilisation in mated ewes. The data in Table 5.6 are misleading in one respect: if the conception rate for the first cycle is only 50% to 60% due to too few rams, it should rise to around 70% for the second and third cycles (by which time the ‘functional’ joining ratio is much increased).

5.4.8 Failure of Fertilisation Due to Other Ram Factors When natural mating is well managed, nearly all ova should be fertilised. Failure of the ram to deposit into the vagina adequate, normal, motile sperm is occasionally a cause of low fertility. This could possibly result from the use of too few rams or overworked rams, but it is more often related to abnormalities of the testes or other parts of the male reproductive tract due to infectious diseases or injury. Note, however, that rams with brucellosis and some other genital infections can often still produce ejaculates with good numbers of normal, motile sperm. Defective spermatozoa commonly result from the excessive heating of rams. Some rams, however, routinely produce ejaculates of low quality for no obvious reason.

5.5 ABNORMALITIES AND DISEASES AFFECTING RAM FERTILITY 5.5.1 Epididymitis Caused by Brucella ovis Infection (Ovine Brucellosis, OB) Epididymitis caused by Brucella ovis is the most common lesion of the genitalia of Merino rams culled from Australian flocks. In one survey, epididymitis was identified in 19% of rams, and B. ovis was associated with 47% of those cases.89 There is a lower flock prevalence of infection in

131

Merinos than in British breeds. The prevalence of infection on some properties may exceed 50% of rams, but this is uncommon. Generally, fertility is not compromised until the proportion of rams with chronic, palpable lesions exceeds 10% to 20%. Economic wastage occurs from extension of the lambing period,90,91 reduction of lambing percentage and an increased size and rate of turnover of the ram team.92

5.5.1.1 Epidemiology Rams can become infected at any age over 4 months.93 Transmission of infection occurs mainly from ram to ram, via the ewe’s vagina principally, but also by homosexual activity between rams.94 Infection can occur by inoculation of mucosal surfaces including the prepuce, conjunctiva and nasal mucosa. Infection in ewes is usually short-lived. Experimental infection of ewes at mating 95 and field evidence96 indicate that infection can persist in the ewe, leading to returns to service, abortion, birth of weak lambs and perinatal mortality. The incidence of infection in ewe flocks is, however, low, and the role of persistently infected ewes in the maintenance of infection in the ram flock is insignificant. In chronically infected rams, active excretion of bacteria in semen probably persists indefinitely.

5.5.1.2 Pathogenesisd Following a bacteraemia there is localisation in the epididymis, usually unilaterally and in the tail, producing degenerative, inflammatory and proliferative changes. The resulting sperm stasis and epithelial damage may result in extravasation of sperm with subsequent spermatic granuloma formation. Histopathological and bacteriological studies suggest that the epididymal tail, ampulla, ductus deferens and seminal vesicles are the most frequently involved sites of infection; the testis and the head of the epididymis are involved less frequently.97,98 Seroconversion (as detected by the warm complement fixation test (CFT)) occurs 10 to 66 days after artificial infection, earlier with more sensitive testing procedures.99 Semen culture is generally positive 5–10 weeks postinfection,98 and lesions caused by the initial infection are usually palpable from nine weeks onwards. (Both of these events can occur sooner than this—positive semen culture and clinically palpable lesions may be detected as soon as four weeks post-infection.93) Some challenged rams never develop any evidence of infection; others develop serological evidence only. These rams recover and are said to have had ‘abortive’ infections.100 Serological reactions decline in recovered animals over a period of four to five months.  The pathogenesis of B. ovis for ewes will be discussed in the Chapter 7.

d

132

CHAPTER 5: Reproduction 1: Factors Affecting Fertility and Fecundity

In animals which remain chronically infected, serological responses remain relatively constant.92

5.5.1.3  Clinical Findings A deterioration in semen quality occurs early in the disease, and the semen contains many leucocytes. In the acute stages of the disease, there is oedema and inflammation of the epididymis and tunics, palpable as a general swelling and a loss of definition of the scrotal contents. There is a systemic reaction which is rarely detected. Regression of the acute syndrome is followed by a latent period of two to three months before chronic lesions with palpable abnormalities develop in one or both sides of the scrotum. The usual chronic lesion is an enlargement of one or both the epididymides, usually in the tail, which is hard due to fibrosis. The epididymis may be two to three times normal size or even more. There is no orchitis, and initially the testes feel normal, but degeneration and atrophy lead to a decline in the size and firmness of the testes. Less commonly, the enlargement and hardening may involve more of the epididymis, or the head only, or it may not involve the epididymis at all, being restricted to one or more of the accessory sex glands.

5.5.1.4 Diagnosis The presence in a flock of a prevalence of chronic epididymal lesions greater than 5% is suggestive of brucellosis. Lesions of chronic epididymitis must be differentiated from those caused by trauma and other bacteria, particularly Actinobacillus seminis. Lesions caused by A. seminis generally show a more acute reaction and are located in the head of the epididymis more frequently than lesions caused by B. ovis. Either semen examination and demonstration of the weakly acid-fast bacilli in smears or semen culture for B. ovis is necessary for a definitive diagnosis. Neither test is particularly sensitive, primarily because of intermittent shedding of the organism by infected rams, and culture may be the more sensitive technique when laboratory procedures are commenced soon after sample collection.101,102 The CFT has long been used in Australia and New Zealand to eradicate the disease from flocks. In 1983, an ELISAe test was developed with a specificity comparable to the warm CFT (0.5% false positives) but significantly higher sensitivity.103 (The increased sensitivity, however, means that some CFT-negative, ELISA-positive rams are detected which will never excrete B. ovis and will eventually become ELISA-negative.) If an investigation is carried out soon after B. ovis is introduced into a flock, a high proportion of rams which e

 Enzyme-linked immunosorbent assay.

will never become excretors may be detected serologically. This fact should be considered when planning eradication programmes. Testing immediately after joining or soon after sexual activity has started in flocks of young rams could lead to the identification and culling of recently infected animals, many of which will ultimately recover and become serologically negative. Rams with low CFT titres (1:8 or 1:16) are frequently found to be uninfected and are probably recovering from abortive infections. Currently, it is recommended that lowtitre-positive animals with no palpable lesions be isolated from other rams and retested after four weeks. Persistent low titres may warrant the slaughter and detailed necropsy examination of the rams in question so that the true status of the flock can be determined.104

5.5.1.5  Control and Elimination 5.5.1.5.1  Eradication by Isolation of Old Rams from Young Rams In commercial flocks, brucellosis can be readily eradicated by isolating the existing, infected ram flock, purchasing replacement rams from accredited OB-free studs and keeping them at all times separate from the old rams. Eradication from the older rams can be attempted by ‘test and slaughter’, or these rams can be used for mating and cast for age progressively over three to four years. There is a significant danger that the infected rams will gain access to the young rams and cause a breakdown, so the shorter the duration of the ‘two-flock’ system, the safer. 5.5.1.5.2  Eradication by ‘Test and Slaughter’ In ram-breeding flocks, a programme of testing (ELISA serology) and culling for slaughter of any reactors (a ‘test and slaughter’ strategy) will successfully eradicate brucellosis, provided new cases are detected before they commence excretion of B. ovis organisms, possibly as early as four weeks post-infection.93 Serial testing should be performed, therefore, every three weeks and all positive reactors slaughtered.105 Any older rams with lesions of epididymitis should be culled regardless of the serological result because some false negative results can occur with chronically infected animals.98 Infection of ewes is potentially a source of breakdown during eradication, but this is rarely a problem of any practical significance. 5.5.1.5.3  Control by Vaccination (but Not in Australia) Vaccination against OB has been used in Australia as a control measure but is no longer permitted. The usual practice was the simultaneous administration of a formalin-killed B. ovis saline-in-oil emulsion and Brucella abortus strain 19 vaccine, although the equal efficacy of some B. ovis vaccines when

5.5 A bnor m a l i t i e s a n d D i s e a s e s A f f e c t i ng R a m Fe r t i l i t y

administered twice, two weeks apart, was demonstrated.106 Brucella melitensis Rev1 vaccine, a modified live vaccine developed for the control of B. melitensis infection, is now considered a better choice for B. ovis control. Vaccination is no longer used as a way of limiting B. ovis infection in Australia but is used as a control measure in some countries.107 5.5.1.5.4  Accredited OB-Free Flock Scheme Voluntary accreditation schemes for ram breeders operate in all Australian states. In flocks to be accredited, all rams, cryptorchids and teasers over 4 months of age are subject to veterinary examination by palpation of the scrotal contents, and those over 10 months of age are serologically tested. Initial accreditation requires two consecutive negative tests at an interval of 60 to 180 days combined with a process of enquiry and inspection by the certifying veterinarian to ensure that the farm biosecurity is adequate. Subsequent testing, performed annually for three years, and then biennially, involves the palpation of all rams, cryptorchids and teasers over 10 months and blood testing of all over 2½ months of age. In large ram flocks, provisions exist for testing a sample of the sale rams, rather than the entire flock, provided the retained stud sires have been tested and found clean. Testing must be accompanied by restrictions on the introduction of further rams into the flock to ensure those animals are also free of OB. The testing procedure is performed by private practitioners, and the register of accredited flocks is maintained by State Departments of Agriculture. The flock owner pays all costs incurred by the practitioner and the laboratory.

5.5.2  Other Causes of Epididymitis After Brucella ovis, two bacterial species dominate the list of infectious causes of epididymitis in rams. These are Actinobacillus seminis and Histophilus somni. Both are gramnegative pleomorphic organisms, and the epidemiology and pathogenesis of both infectious agents in sheep are so similar that they may, for many purposes, be considered together. The two species are genetically and phenotypically similar, and it has been proposed that one may be a variant of the other.108,109

5.5.2.1  Actinobacillus seminis Epididymitis Actinobacillus seminis was first reported as a cause of epididymitis in rams in 1960 in Australia,110 and there have been numerous reports of A. seminis epididymitis from other countries since then.111 What is currently understood or hypothesised about the epidemiology of infection with A. seminis in sheep flocks has been summarised by Al-Katib and Dennis (2009)111. The organism is not persistent in the

133

environment outside sheep, but fomites may be a shortterm source of infection following contamination by infected semen or discharges from the genital tract of an infected ewe. Transmission between animals can be venereal or non-venereal, and transmission from ewes to perinatal lambs seems likely. Such transmission may be postnatal—through umbilical infection, for example—or prenatal. In young rams, organisms can often be isolated from the prepuce in the absence of any clinical signs, but the frequency of infection of the prepuce declines with age and is significantly less common in rams over 12 months of age. In some individuals, however, ascending infection from the prepuce, or possibly a bacteraemic episode, may lead to infection of the testes, epididymides or accessory sex organs.112 Infection in the epididymis and testis can be asymptomatic or can begin as an acute purulent epididymitis. Those with clinical signs of acute infection tend to have a progressive course, developing chronic epididymitis. Those with less obvious clinical signs may develop chronic lesions or may become free of infection spontaneously. Infected rams usually have low fertility, and chronic cases develop bilateral testicular atrophy. The epididymitis is clinically indistinguishable from brucellosis.113 Persistent subclinical infection can also occur, in which abnormalities are undetectable on clinical examination but organisms are present in semen. Orchitis is a more common additional finding to epididymitis with A. seminis infection than with B. ovis infection. Actinobacillus seminis has also been associated with severe posthitis of a ram and polyarthritis in lambs in Australia,114 as well as metritis, mastitis and abortion in ewes in the UK.115

5.5.2.2  Histophilus somni Epididymitis Histophilus somni is a relatively new species name which includes organisms formerly known as Histophilus ovis, Haemophilus somnus and Haemophilus agni,116 but many publications still refer to isolates from sheep as Histophilus ovis. The names are used interchangeably here, depending on the name given in the cited reference. Histophilus ovis has been reported as causing epididymitis, suppurative polyarthritis in lambs, meningoencephalitis in adult sheep and mastitis in ewes.117 The epidemiology of H. ovis in sheep flocks is uncertain, but the occurrence of polyarthritis caused by this organism in early postnatal lambs (before marking) and the isolation of H. ovis from the genital tract of ewes and prepuce of young rams suggest that the reservoir of infection in flocks is the genital tract of ewes and, possibly, rams.118 Infection of the epididymis and testis may be an occasional sequel of

134

CHAPTER 5: Reproduction 1: Factors Affecting Fertility and Fecundity

a preputial infection of young rams which does not remain localised to the prepuce or resolve spontaneously with age. Establishing an aetiological diagnosis of epididymitis is often important, although serological tests will generally be sufficient to confirm Brucella infections. Serological tests are available for H. somni and A. seminis, but many normal animals have antibodies against them, and cross reactions with each other can confuse the diagnosis. Culture of the organisms from semen is complicated by their slow growth, lack of selective media and likelihood of overgrowth by other semen microflora. Recently, PCR f tests have been developed which can quickly and reliably identify the two organisms and distinguish between them.119

5.5.2.3  Miscellaneous Infections Causing Epididymitis Trueperella pyogenes, Actinobacillus lignieresii, Corynebacterium pseudotuberculosis, Yersinia pseudotuberculosis, Escherichia coli (causing abscessation with fistula formation in the scrotum and orchitis120) and B. abortus (strain 19) have been reported in sporadic cases of epididymitis.

5.5.3  Non-Specific Abnormalities of the Epididymis 5.5.3.1  Spermatocoele and Spermatic Granuloma A spermatocoele is a cystic dilatation of the epididymal duct with the accumulation of sperm in the cyst. It follows acquired or congenital occlusion of the duct. If extravasation of sperm occurs, the stromal tissue produces a characteristic granulomatous response. Spermatic granulomas which develop secondarily to congenital occlusion are usually in the head of the epididymis. Congenital obstruction in rams and male goats is not uncommon and is usually unilateral. Obstruction of the epididymal duct in the head, body or tail leads to testicular degeneration, although the process is relatively slow—the efferent ducts are able to resorb most of the products of the seminiferous epithelium except sperm. Obstruction of the efferent ducts, in contrast, leads rapidly to testicular atrophy.121 Spermatic granulomas which develop secondarily to bacterial infection are usually found in the tail of the epididymis because the majority of bacterial infections start, and are most severe, at that site. The two most common bacterial infections of epididymides in Australian sheep flocks are those caused by Brucella ovis and by Actinobacillus seminis. The palpable lesion of the epididymis typical of B.  Polymerase chain reaction, a technique commonly used to amplify DNA segments such that the presence of small amounts can be detected by further tests.

f

ovis infection is, in fact, a spermatic granuloma. Spermatic granulomas following obstruction of the duct may also be caused by trauma.122

5.5.4  Testicular Abnormalities 5.5.4.1 Cryptorchism Cryptorchism (or cryptorchidism) can be either unilateral or bilateral—the unilateral form is sometimes referred to as monorchism or monorchidism and is more common than the bilateral form.123 When unilateral, it is usually the right testis which fails to descend. In Merino sheep the foetal testes normally pass through the inguinal canal between days 75 and 80 post-conception, and rarely, if ever, will a retained testis descend through the inguinal canal after birth.124 The retained testis or testes may be in the abdomen or inguinal canal, where the high testicular temperature prevents normal spermatogenesis. Rams with bilateral cryptorchism are sterile, but unilateral cryptorchids are likely to be fertile. While their fertilising capacity is probably reduced to some extent by the functional loss of one testis, the fully descended testis does often show some compensatory hypertrophy. In the mid-20th century the incidence of cryptorchism in Australian Merino sheep was estimated to be around 0.4%,125,126 although some flocks reported higher incidences. A later study found an incidence 10-fold higher.127 An incidence of 0.6% with substantial variation between flocks has been reported in UK sheep flocks.123 The inheritance of the trait suggests that it is inherited as a recessive gene with a low degree of penetrance or as a threshold polygenic trait.128 In ram-breeding flocks, the cryptorchid animal should be culled, but attempts to further reduce the incidence in the flock are usually only advisable or necessary if the frequency of cryptorchidism is high. In those cases, the parents and all full siblings of the affected animal should be culled. In commercial flocks, unilateral cryptorchids could feasibly be used to produce offspring for slaughter, although, if the genes contributing to cryptorchidism are already present in the ewe flock to a significant degree, there may be an increased incidence of cryptorchidism in the lambs. If the lambs are sold for slaughter entire, this may not be a problem, but if the custom is to castrate all male lambs, cryptorchids are generally considered a nuisance. Most commercial producers choose not to use unilateral cryptorchid rams as sires. According to Dolling and Brooker, as cited in other sources,129 an association between polledness and cryptorchism has been reported in some studies but is not present in the Australian Merino.

5.5 A bnor m a l i t i e s a n d D i s e a s e s A f f e c t i ng R a m Fe r t i l i t y

5.5.4.2 Hypoplasia Once testes have descended into the scrotum they should increase in size, gradually at first and more quickly at and after puberty. Bilateral small testes in young rams can occur as a result of undernutrition, in which case the size and condition of the animal also reflect the poor growth. Small testes can also be the result of a failure to develop for, presumably, genetic reasons, in which case the condition is one of hypoplasia. That hypoplasia is the reason for the underdevelopment is most obvious when the ram is young, when it is in reasonable or better nutritional condition, and if only one testis is affected. Testicular hypoplasia can be either unilateral or bilateral (Figure 5.7). Both unilateral and bilateral forms may have an inherited basis. In some cases, the occurrence of one or two abnormally small testes in a young ram may be due to late or delayed development, in which case the hypoplasia may be temporary.130 In older rams, hypoplasia must be differentiated from atrophy in which a previously normally developed testis becomes smaller and soft, usually following a local or systemic illness. Hypoplasia of the testes of rams has been associated with zinc deficiency experimentally, and the possibility exists that natural cases could occur in the field in some regions.131

5.5.4.3 Degeneration The testicular germinal epithelium is very sensitive to many adverse influences. Degeneration may be unilateral or bilateral, which may help determine whether the cause is systemic or local. The degenerated testis may remain a normal size but be soft and flabby, or it may become small and firm. Softness and flabbiness often indicate rapidly

135

progressing degeneration, while fibrosis takes several months to develop. Sperm production is reduced, and the semen becomes thin and milky or watery. Regeneration can occur but takes longer than the degeneration. The causes can be grouped under a number of headings: • Thermal: Maintaining rams at 35 °C for periods exceeding four days leads to a loss of motility and an increased proportion of abnormal sperm. If the period is extended there is a measurable decrease in the concentration of sperm and, ultimately, a cessation of spermatogenesis. • Local or systemic infection: Fever, toxaemia or local inflammation. • Nutritional deficiencies: Vitamin A, phosphorus, severe deficiencies of protein or energy which lead to very low condition score (1–1½). • Vascular lesions. • Obstructive lesions of the efferent tubules: The backpressure leads rapidly to the degeneration of seminiferous epithelium. The testes degenerate but are enlarged with fluid.

5.5.5  Other Abnormalities Detected on Scrotal Palpation 5.5.5.1  Scrotal Hernia Scrotal hernia occurs occasionally in rams. The lesion is usually detected when rams are examined for genital soundness or when the swelling in the scrotum is observed at crutching or shearing. The abnormality was detected as an incidental finding in 0.5% of 2332 Merino rams examined in flocks in Queensland in the 1960s.132 A higher incidence (8% of rams) with a possibly inherited predisposition has been reported in another Merino flock in which in-breeding was common practice.133 Rams with scrotal hernia are likely to have reduced fertility due to testicular degeneration and, because the abnormality may have a genetic component, should not be used for breeding. While it may be considered satisfactory by some breeders to use a ram with a scrotal hernia to produce terminal lambs, they should be made aware that congenital inguinal hernias in lambs that are castrated may lead to evisceration through the castration wound or entrapment of intestine in the rubber ring.

5.5.5.2  Scrotal Abscess Figure 5.7  Unilateral testicular hypoplasia. The small testis is grossly normal other than being much smaller than expected. The condition is more commonly unilateral than bilateral and, if detected in a young ram, may be a temporary condition. Source: Kym A Abbott.

Abscesses of the scrotum and inguinal lymph nodes occur occasionally in rams, and the incidence tends to increase with age. Some abscesses are the result of shearing cuts. Some scrotal abscesses are lesions of caseous lymphadenitis (CLA) caused by Corynebacterium pseudotuberculosis and occur in the scrotal fascia in the neck of the scrotum,

136

CHAPTER 5: Reproduction 1: Factors Affecting Fertility and Fecundity

palpably distinct from the spermatic cord.134 Closed lesions not involving the testes, epididymis or spermatic cords may not impair fertility. Open, draining lesions of the scrotum require treatment or culling of the ram. Surgical drainage and debridement of scrotal abscesses in valuable rams can be successful provided the lesion does not extend to the testis or epididymis.

5.5.5.3 Varicocoele A varicocoele is a saccular dilatation of the spermatic vein and is usually of little or no significance. Bilateral varicocoeles of long duration may adversely affect semen quality (possibly due to anoxia) or they may, if large enough, incapacitate rams so that they are unable to walk normally due to pain. They do, however, increase in size very slowly and occasionally reach large proportions.

5.5.5.4  Scrotal Mange Mange of the scrotum, caused by Chorioptes bovis, is associated with seminal degeneration and testicular atrophy.135 (See Chapter 15.)

5.5.6  Other Lesions of the Male Genitalia 5.5.6.1  Balanitis and Posthitis Balanoposthitis, balanitis and posthitis are described at length in Chapter 19. Balanoposthitis (pizzle rot or sheath rot) is caused by Corynebacterium renale under particular dietary conditions and is principally a problem of wethers, but it may also occur in rams. A different condition—a severe, ulcerative balanitis—occurs sporadically in rams, particularly in Border Leicester rams, but also in other British breeds. Signs of the disease are often observed first during joining and may occur concurrently with vulvovaginitis in the ewe flock.

RECOMMENDED READING Greig A (2007) Ram infertility. In: Diseases of sheep, ed ID Aitken. 4th ed. Blackwell Science: London, pp. 87–94. West DM, Bruere AN and Ridler AL (2018) Genital soundness in the ram and diseases of the genitalia. In: The sheep: Health, disease & production. 4th ed. Massey University Press: Auckland, NZ, pp. 16–38.

GENERAL REFERENCES Lindsay DR and Pearce DT, eds (1984) Reproduction in sheep. Australian Academy of Science: Canberra. Lynch JJ (1990) Physiology and behaviour of lambs in the perinatal period. In: Sheep medicine. Proceedings No. 141. University of Sydney Postgraduate Committee in Veterinary Science: Sydney, Australia, pp. 335–56.

Mellor DJ (1990) Constraints on lamb survival. In: Sheep medicine. Proceedings No. 141. University of Sydney Postgraduate Committee in Veterinary Science: Sydney, Australia, pp. 77–83. Oldham CM, Martin GB and Purvis IW, eds (1990) Reproductive physiology of Merino sheep: Concepts and consequences. The University of Western Australia: Perth.

REFERENCES 1 Afolayan RA, Fogarty NM, Gilmour AR et al. (2008) Reproductive performance and genetic parameters in first cross ewes from different maternal genotypes. J Anim Sci 86 804–14. https://doi.org/10.2527/jas.2007-0544. 2 Restall BJ, Brown GH, Blockey MB et al. (1976) Assessment of reproductive wastage in sheep. 1. Fertilization failure and early embryonic survival. Aust J Exp Agric Anim Husb 16 329–35. https://doi.org/10.1071/ EA9760329. 3 Yeates NTM (1949) The breeding season of the sheep with particular reference to its modification by artificial means using light. J Agric Sci 39 1–42. https://doi.org/10.1017/ S0021859600004299. 4 Radford HM (1960) Photoperiodism and sexual activity in Merino ewes. Aust J Agric Res 11 139–46. https://doi. org/10.1071/AR9610139. 5 Hart DS (1950) Photoperiodicity in Suffolk sheep. J Agric Sci 40 143–9. https://doi.org/10.1017/ S0021859600045597. 6 Underwood EJ, Shier FL and Davenport N (1944) Studies in sheep husbandry in WA V: The breeding season of Merino, crossbred and British breed ewes in the agricultural districts. J Agric WA II 135–43. 7 Smith ID (1967) The breeding season in British breeds of sheep in Australia. Aust Vet J 43 59–62. https://doi. org/10.1111/j.1751-0813.1967.tb15064.x. 8 Edgar DG and Bilkey DA (1963) The influence of rams on the onset of the breeding season in ewes. Proc NZ Soc Anim Prod 23 79–87. 9 Schinckel PG (1954) The effect of the ram on the incidence and occurrence of oestrus in ewes. Aust Vet J 30 189–95. https://doi.org/10.1111/j.1751-0813.1954.tb08198.x. 10 Pearce DT and Oldham CM (1984) The ram effect, its mechanism and application to the management of sheep. In: Reproduction in sheep, eds DR Lindsay and DT Pearce. Australian Academy of Science: Canberra, pp. 26–34. 11 Pearce GP and Oldham CM (1988) Importance of non-olfactory ram stimuli in mediating ram-induced ovulation in the ewe. J Reprod Fertil 84 333–9. https://doi. org/10.1530/jrf.0.0840333. 12 Jorre de St Jorre T, Hawken PAR and Martin GB (2012) Role of male novelty and familiarity in male-induced LH secretion in female sheep. Reprod Fert Develop 24 523–30. https://doi.org/10.1071/RD11085. 13 Scaramuzzi RJ and Radford HM (1983) Factors affecting ovulation rate in the ewe. J Reprod Fert 69 353–67.

R e f e r e nc e s

14 Fletcher IC, Geytenbeek PE and Allden WG (1970) Interaction between the effects of nutrition and season of mating on reproductive performance in crossbred ewes. Aust J Exp Agric Anim Husb 10 393–6. https://doi. org/10.1071/EA9700393. 15 Dun RB, Ahmed W and Morrant AJ (1960) Annual reproductive rhythm in Merino sheep related to the choice of a mating time at Trangie central western New South Wales. Aust J Agric Res 11 805–56. https://doi. org/10.1071/AR9600805. 16 Kenyon PR, Morel PCH, Morris ST et al. (2006) The effect of length of use of teaser rams prior to mating and individual liveweight on the reproductive performance of ewe hoggets. NZ Vet J 54 91–5. https://doi.org/10.1080/00 480169.2006.36618. 17 Kenyon PR, Viñoles C and Morris ST (2012) Effect of teasing by the ram on the onset of puberty in Romney ewe lambs. New Zeal J Agr Res 55 283–91. https://doi.org/10.1 080/00288233.2012.693105. 18 Cumming IA (1977) Relationships in the sheep of ovulation rate with liveweight, breed, season and plane of nutrition. Aust J Exp Agric Anim Husb 17 234–40. https://doi. org/10.1071/EA9770234. 19 Morley FHW, White DH, Kenney PA et al. (1978) Predicting ovulation rate from liveweight in ewes. Agric Syst 3 27–45. https://doi.org/10.1016/0308521X(78)90004-5. 20 Kleeman DO and Walker SK (2005) Fertility in South Australian Merino flocks: Relationships between reproductive traits and environmental cues. Theriogenology 63 2416–33. https://doi.org/10.1016/j. theriogenology.2004.09.052. 21 Fletcher IC (1971) Effects of nutrition, liveweight and season on the incidence of twin ovulation in South Australian strong-wool Merino ewes. Aust J Agric Res 22 321–30. https://doi.org/10.1071/AR9710321. 22 Behrendt R, van Burgel AJ, Bailey A et al. (2011) On-farm paddock scale comparisons across southern Australia confirm that increasing the nutrition of Merino ewes improves their production and the lifetime performance of their progeny. Anim Prod Sci 51 805–12. https://doi. org/10.1071/AN10183. 23 Trompf JP, Gordon DJ, Behrendt R et al. (2011) Participation in Lifetime Ewe Management results in changes in stocking rate, ewe management and reproductive performance on commercial farms. Anim Prod Sci 51 866–72. https://doi.org/10.1071/AN10164. 24 Coop IE (1966) Effect of flushing on reproductive performance of ewes. J Agric Sci Camb 67 305–23. https:// doi.org/10.1017/S0021859600017317. 25 Linday DR (1976) The usefulness to the animal producer of research findings in nutrition on reproduction. Proc Aust Soc Anim Prod 11 217–24. 26 Knight TW, Oldham CM and Lindsay DR (1975) Studies in ovine infertility in agricultural regions in Western

27

28

29

30

31

32

33

34

35

36

37

38

137

Australia: The influence of a supplement of lupins (Lupinus angustifolius cv. Uniwhite) at joining on the reproductive performance of ewes. Aust J Agric Res 26 567–75. https:// doi.org/10.1071/AR9750567. Van Barneveld RJ (1999) Understanding the nutritional chemistry of lupins (Lupinus spp) seed to improve livestock production efficiency. Nutr Res Rev 12 203–30. https://doi. org/10.1079/095442299108728938. Teleni E, King WR, Rowe JB et al. (1989) Lupins and energy-yielding nutrients in ewes I: Glucose and acetate biokinetics and metabolic hormones in sheep fed a supplement of lupin grain. Aust J Agric Res 40 913–24. https://doi.org/10.1071/AR9890913. Teleni E, Rowe JB, Croker KP et al. (1989) Lupins and energy-yielding nutrients in ewes II: Responses in ovulation rate in ewes to increased availability of glucose, acetate and amino acids. Reprod Fertil Dev 1 117–25. https://doi. org/10.1071/RD9890117. Somchit A, Campbell BK, Khalid M et al. (2007) The effect of short-term nutritional supplementation of ewes with lupin grain (Lupinus luteus), during the luteal phase of the estrous cycle on the number of ovarian follicles and the concentrations of hormones and glucose in plasma and follicular fluid. Theriogenology 68 1037–46. https://doi. org/10.1016/j.theriogenology.2007.08.001. Brien FD, Cumming IA and Baxter RW (1977) Effect of feeding a lupin grain supplement on reproductive performance of maiden and mature ewes. J Agric Sci Camb 89 437–43. https://doi.org/10.1017/S0021859600028367. Alexander G, Bradley LR and Stevens D (1993) Effect of age and parity on maternal behaviour in single-bearing ewes Aust J Exp Agr 33 721–8. https://doi.org/10.1071/ EA9930721. Quinlivan TD, Martin CA, Taylor WB et al. (1966) Estimates of pre- and perinatal mortality in the New Zealand Romney Marsh ewe I: Pre- and perinatal mortality in those ewes that conceived to one service. J Reprod Fertil 11 379–90. https://doi.org/10.1530/jrf.0.0110379. Allison AJ (1977) Flock mating in sheep II: Effect of number of ewes per ram on mating behaviour and fertility of two-tooth and mixed-age Romney ewes run together. New Zeal J Agr Res 20 123–8. https://doi.org/10.1080/002 88233.1977.10427315. Tilbrook AJ and Cameron AWN (1989) Ram mating preferences for woolly rather than recently shorn ewes. Appl Anim Behav Sci 24 301–12. https://doi. org/10.1016/0168-1591(89)90058-0. Adams NR (1990) Permanent infertility in ewes exposed to plant oestrogens. Aust Vet J 67 197–201. https://doi. org/10.1111/j.1751-0813.1990.tb07758.x. Cox RI and Braden AW (1974) The metabolism and physiological effects of phyto-oestrogens in livestock. Proc Aust Soc Anim Prod 10 122–9. Adams NR (1986) Measurement of histological changes in the cervix of ewes after prolonged exposure to oestrogenic

138

39

40

41

42

43

44

45

46

47

48

49

50

51

52

CHAPTER 5: Reproduction 1: Factors Affecting Fertility and Fecundity

clover or oestradiol-17ß. Aust Vet J 63 279–82. https://doi. org/10.1111/j.1751-0813.1986.tb08066.x. Adams NR (1976) Cervical mucus changes in infertile ewes previously exposed to oestrogenic subterranean clover. Res Vet Sci 21 59–63. https://doi.org/10.1016/S00345288(18)33394-0. Maxwell JAL (1970) Field observations on four outbreaks of maternal dystocia in the Merino ewe. Aust Vet J 46 533– 6. https://doi.org/10.1111/j.1751-0813.1970.tb06640.x. Braden AWH, Southcott WH and Moule GR (1964) Assessment of oestrogenic activity of pastures by means of increase of teat length in sheep. Aust J Agric Res 15 142–52. https://doi.org/10.1071/AR9640142. Little DL and Beale PE (1988) Renovation of Yarloop subterranean clover pastures with Trikkala. Aust J Exp Agric 28 737–45. https://doi.org/10.1071/EA9880737. Lightfoot RJ and Wroth RH (1974) The mechanism of temporary infertility in ewes grazing oestrogenic subterranean clover prior to and during joining. Proc Aust Soc Anim Prod 10 130–4. Morley FHW, Axelsen A and Bennet D (1966) Recovery of normal fertility after grazing on oestrogenic red clover. Aust Vet J 42 204–6. https://doi. org/10.1111/j.1751-0813.1966.tb04690.x. Coop IE (1977) Depression of lambing percentage from mating on Lucerne. Proc NZ Soc Anim Prod 37 149–51. Nancarrow CD (1994) Embryonic mortality in the ewe and doe. In: Embryonic mortality in domestic species, eds RD Geisert and MT Zavy. CRC Press: Boca Raton, FL, pp. 79–97. Edey TN (1979) Embryo mortality. In: Sheep breeding: Studies in the agricultural and food sciences, eds GL Tomes, DE Robertson and RJ Lightfoot. 2nd ed. revised by William Haresign. Butterworths: London, pp. 315–25. O’Connell AR, Demmers KJ, Smaill B et al. (2016) Early embryo loss, morphology, and effect of previous immunization against androstenedione in the ewe. Theriogenology 86 1285–93. https://doi.org/10.1016/j. theriogenology.2016.04.069. Bazer FW, Spencer TE and Ott TL (1997) Interferon Tau: A novel pregnancy recognition signal. Am J Reprod Immunol 37 412–20. https://doi. org/10.1111/j.1600-0897.1997.tb00253.x. Shorten PR, Peterson AJ, O’Connell AR et al. (2010) A mathematical model of pregnancy recognition in mammals. J Theor Biol 266 62–9. https://doi. org/10.1016/j.jtbi.2010.06.005. Edey TN (1967) Early embryonic death and subsequent cycle length in the ewe. J Reprod Fertil 13 437–43. https:// doi.org/10.1530/jrf.0.0130437. Geisler PA, Newton JE and Mohan AE (1977) A mathematical model of fertilization failure and early embryonic mortality in sheep. J Agric Sci Camb 89 309–17. https://doi.org/10.1017/S0021859600028239.

53 Wikins JF and Croker KP (1990) Embryonic wastage in ewes. In: Reproductive physiology of Merino sheep—concepts and consequences, eds CM Oldham, GB Martin and IW Purvis. University of Western Australia: Perth, pp. 169–77. 54 Lindsay DR, Knight TW, Smith JF et al. (1975) Studies in ovine fertility in agricultural regions of Western Australia: Ovulation rate, fertility and lambing performance. Aust J Agric Res 26 189–98. https://doi.org/10.1071/AR9750189. 55 Lincoln GA, Lincoln CE and McNeilly AS (1990) Seasonal cycles in the blood plasma concentration of FSH, inhibin and testosterone, and testicular size in rams of wild, feral and domesticated breeds of sheep. J Reprod Fertil 88 623–33. https://doi.org/10.1530/jrf.0.0880623. 56 D’Occhio MJ and Brooks DE (1983) Seasonal changes in plasma testosterone concentration and mating activity in border Leicester, Poll Dorset, Romney and Suffolk rams. Aust J Exp Agric Anim Husb 23 248–53. https://doi. org/10.1071/EA9830248. 57 Ryder ML (1983) Sheep and man. MPG Books Ltd: Cornwall, UK, p. 460. 58 Martin GB, Hötzel MJ, Blache D et al. (2002) Determinants of the annual pattern of reproduction in mature male Merino and Suffolk sheep: Modification of responses to photoperiod by an annual cycle in food supply. Reprod Fertil Dev 14 165–75. https://doi.org/10.1071/ RD02010. 59 Bremner WJ, Cumming IA and Winfield C (1984) A study of the reproductive performance of mature Romney and Merino rams throughout the year. In: Reproduction in sheep, eds DR Lindsay and DT Pearce. Australian Academy of Science: Canberra, pp. 16–19. 60 Lincoln GA and Davidson W (1977) The relationship between sexual and aggressive behaviour, and pituitary and testicular activity during the seasonal sexual cycle of rams, and the influence of photoperiod. J Reprod Fertil 49 267–76. https://doi.org/10.1530/jrf.0.0490267. 61 Murray PJ, Rowe JB and Petrhick DW (1991) Effect of season and nutrition on scrotal circumference of Merino rams. Aust J Exp Agr 31 753–6. https://doi.org/10.1071/ EA9910753. 62 Masters DG and Fels HE (1984) Seasonal changes in the testicular size of grazing rams. Proc Aust Soc Anim Prod 15 444–7. 63 Sutherland SRD and Martin GB (1980) The effect of a supplement of lupin seed on the testicular size and LH profiles of Merino and Booroola rams. Proc Aust Soc Anim Prod 13 459. 64 Kleeman DO, Kelly JM, Arney LJ et al. (2014) Positive effects of melatonin treatment on the reproductive performance of young border Leicester rams mated to Merino ewes in Spring: preliminary observations. Reprod Dom Anim 49 894–8. https://doi.org/10.1111/rda.12387. 65 Kleeman DO, Kelly JM, Arney LJ et al. (2021) Sexual behaviour, semen quality and fertility of young Border Leicester rams administered melatonin during spring.

R e f e r e nc e s

66

67

68

69

70

71

72

73

74

75

76

77

78

Anim Reprod Sci 231 106804. https://doi.org/10.1016/j. anireprosci.2021.106804. Kleeman DO, Kelly JM, Arney LJ et al. (2022) Melatonin dose: Testicular and testosterone response in border Leicester rams during spring. Livest Sci 260 104298. https://doi.org/10.1016/j.livsci.2022.104928. Lino BF (1972) The output of spermatozoa in rams II: Relationship to scrotal circumference, tests weight, and the number of spermatozoa in different parts of the urogenital tract. Aust J Biol Sci 25 359–66. https://doi.org/10.1071/ BI9720359. Foster RA, Ladds PW, Hoffmann D et al. (1989) The relationship of scrotal circumference to testicular weight in rams. Aust Vet J 66 20–2. https://doi. org/10.1111/j.1751-0813.1989.tb09707.x. Mattner PE and Braden AWH (1967) Studies in flock mating of sheep 2: Fertilization and prenatal mortality. Aust J Exp Agric Anim Husb 11 110–16. https://doi. org/10.1071/EA9670110. Raadsma HW and Edey TN (1985) Mating performance of paddock-mated rams I: Changes in mating performance, ejaculate characteristics and testicular size during the joining period. Anim Reprod Sci 8 79–99. https://doi. org/10.1016/0378-4320(85)90075-2. Synott AL, Fulkerson WJ and Lindsay DR (1981) Sperm output by rams and distribution amongst ewes under conditions of continual mating. J Reprod Fertil 61 355–61. https://doi.org/10.1530/jrf.0.0610355. Salamon S (1962) Studies on the artificial insemination of Merino sheep III: The effect of frequent ejaculation on semen characteristics and fertilizing capacity. Aust J Ag Res 13 1137–50. https://doi.org/10.1071/ AR9621137. Lindsay DR and Ellsmore J (1968) The effect of breed, season and competition on mating behaviour of rams. Aust J Exp Agric Anim Husb 8 649–52. https://doi.org/10.1071/ EA9680649. Synnott AL and Fulkerson WJ (1984) Influence of social interaction between rams on their serving capacity. App Anim Ethol 11 283–9. https://doi.org/10.1016/03043762(84)90035-X. Lightfoot RJ and Smith JAC (1968) Studies on the number of ewes joined per ram for flock matings under paddock conditions. Aust J Agric Res 19 1029–42. https://doi. org/10.1071/AR9681029. Allison AJ (1975) Flock mating in sheep. I Effect of number of ewes joined per ram on mating behaviour and fertility. New Zeal J Agr Res 18 1–8. https://doi.org/10.1080/00288 233.1975.10430379. Dun RB (1955) Puberty in Merino rams. Aust Vet J 31 104–6. https://doi.org/10.1111/j.1751-0813.1955. tb05515.x. Skinner JD and Rowson LEA (1968) Puberty in Suffolk and cross-bred lambs. J Reprod Fertil 16 479–88. https://doi. org/10.1530/jrf.0.0160479.

139

79 Belibasaki S and Kouimtzis S (2000) Sexual activity and body and testis growth in prepubertal ram lambs of Friesland, Chios, Karagouniki and Serres dairy sheep in Greece. Small Rumin Res 37 109–13. https://doi. org/10.1016/S0921-4488(99)00131-5. 80 Watson RH, Sapsford CS and McCance I (1956) The development of the testis, epididymis and penis in the young Merino ram. Aust J Agric Res 7 575–90. https://doi. org/10.1071/AR9560574. 81 Swan AA, Brown DJ and Banks RG (2008) Genetic progress in the Australian sheep industry. Proc Assoc Advmt Anim Breed Genet 18 326–9. 82 Murray PJ, Rowe JB, Pethick DW et al. (1990) The effect of nutrition on testicular growth in the Merino ram. Aust J Agric Res 41 185–95. https://doi.org/10.1071/AR99 00185. 83 De Blockey MA and Wilkins JF (1984) Field application of the ram serving capacity test. In: Reproduction in sheep, eds DR Lindsay and DT Pearce. Australian Academy of Science: Canberra, p. 53. 84 Purvis IW, Edey TN, Kilgour RJ et al. (1984) The value of testing young rams for serving capacity. In: Reproduction in sheep, eds DR Lindsay and DT Pearce. Australian Academy of Science: Canberra, p. 59. 85 Galloway DB (1983) Reproduction in the ram. In: Sheep production and preventive medicine. Proceedings No. 67. University of Sydney Post-Graduate Committee in Veterinary Science: Sydney, Australia, pp. 163–95. 86 Kilgour RJ (1993) The relationship between ram breeding capacity and flock fertility. Theriogenology 40 277–85. https://doi.org/10.1016/0093-691X(93)90265-7. 87 Preston BT, Stenson IR, Pemberton JM et al. (2003) Overt and covert competition in a promiscuous mammal: The importance of weaponry and testes size to male reproductive success. Proc R Soc Lond B Biol Sci 270 633–40. https://doi.org/10.1098/rspb.2002.2268. 88 Fowler DG and Jenkins LD (1976) The effects of dominance and infertility of rams on reproductive performance. Appl Anim Ethol 2 327–37. https://doi. org/10.1016/0304-3762(76)90066-3. 89 Foster RA, Ladds, PW, Hoffman D et al. (1989) Pathology of reproductive tracts of Merino rams in North Western Queensland. Aust Vet J 66 262–4. https://doi. org/10.1111/j.1751-0813.1989.tb13587.x. 90 Hughes KL (1972) Experimental Brucella ovis infection in ewes 1: Breeding performance of infected ewes. Aust Vet J 48 12–17. https://doi.org/10.1111/j.1751-0813.1972. tb02200.x. 91 McGowan B and Schultz G (1956) Epididymitis of rams: Clinical description and field aspects. Cornell Vet 46 277–81. 92 Plant JW (1982) Ovine brucellosis. Agfact A3.9.2 AGdex 432/653. NSW Agriculture, Orange, NSW. 93 Burgess GW, McDonald JW and Norris MJ (1982) Epidemiological studies on ovine brucellosis in

140

94

95

96

97

98

99

100

101

102

103

104

105

106

CHAPTER 5: Reproduction 1: Factors Affecting Fertility and Fecundity

selected ram flocks. Aust Vet J 59 45–7. https://doi. org/10.1111/j.1751-0813.1982.tb02714.x. Plant JW, Eamens GJ and Seaman JT (1986) Serological, bacteriological and pathological changes in rams following different routes of exposure to Brucella ovis. Aust Vet J 63 409–12. https://doi.org/10.1111/j.1751-0813.1986. tb15919.x. Hughes KL (1972) Experimental Brucella ovis infection in ewes 2: Correlation of infection and complement fixation titres. Aust Vet J 48 18–22. https://doi. org/10.1111/j.1751-0813.1972.tb02201.x. Haughey KG, Hughes KL and Hartley WJ (1968) Brucella ovis infection 2: The infection status in breeding flocks as measured by examination of rams and the perinatal lamb mortality. Aust Vet J 44 531–5. https://doi. org/10.1111/j.1751-0813.1968.tb04920.x. Searson JE (1986) Distribution of Brucella ovis in the tissues of rams reacting in a complement fixation test for ovine brucellosis. Aust Vet J 63 30–1. https://doi. org/10.1111/j.1751-0813.1986.tb02872.x. Searson JE (1987) The distribution of histopathological lesions in rams reacting in a complement fixation test for Brucella ovis. Aust Vet J 64 108–9. https://doi. org/10.1111/j.1751-0813.1987.tb09640.x. Burgess GW and Norris MJ (1982) Evaluation of the cold complement fixation test for diagnosis of ovine brucellosis. Aust Vet J 59 23–5. https://doi. org/10.1111/j.1751-0813.1982.tb02706.x. Laws L, Simmons GC and Ludford CG (1972) Experimental Brucella ovis infection in rams. Aust Vet J 48 313–17. https://doi.org/10.1111/j.1751-0813.1972. tb02257.x. Hughes KL and Claxton PD (1968) Brucella ovis infection 1: An evaluation of microbiological, serological and clinical methods of diagnosis in the ram. Aust Vet J 44 41–7. https://doi.org/10.1111/j.1751-0813.1968. tb04951.x. Webb RF, Quinn CA, Cockram FA et al. (1980) Evaluation of procedures for the diagnosis of Brucella ovis infection in rams. Aust Vet J 56 172–5. https://doi. org/10.1111/j.1751-0813.1980.tb05673.x. Lee K, Cargill C and Atkinson H (1985) Evaluation of an enzyme linked-immunosorbent assay for the diagnosis of Brucella ovis infection in rams. Aust Vet J 62 91–3. https:// doi.org/10.1111/j.1751-0813.1985.tb14147.x. Rothwell JT, Searson JE, Links IJ et al. (1986) Examination of rams culled during an ovine brucellosis accredited free flock scheme. Aust Vet J 63 209–11. https://doi. org/10.1111/j.1751-0813.1986.tb02996.x. Gorrie CJR and Rushford BH (1969) Control of ovine brucellosis. Aust Vet J 45 304. https://doi. org/10.1111/j.1751-0813.1969.tb01965.x. Claxton PD (1968) Brucella ovis vaccination of rams. Aust Vet J 44 48–54. https://doi.org/10.1111/j.1751-0813.1968. tb04953.x.

107 Ridler Al and West DM (2011) Control of Brucella ovis infection in sheep. Vet Clinics N Am Food Anim Pract 27 61–6. https://doi.org/10.1016/j.cvfa.2010.10.013. 108 Rycroft AN and Garside LH (2000) Actinobacillus species and their role in animal disease. Vet J 159 18–39. https:// doi.org/10.1053/tvjl.1999.0403. 109 McGillivery DJ, Webber JJ and Dean HF (1986) Characterisation of Histophilus ovis and related organisms by restriction endonuclease analysis. Aust Vet J 63 389–93. https://doi.org/10.1111/j.1751-0813.1986.tb15914.x. 110 Baynes ID and Simmons GC (1960) Ovine epididymitis caused by Actinobacillus seminis. Aust Vet J 36 454–9. https://doi.org/10.1111/j.1751-0813.1960.tb03745.x. 111 Al-Katib WA and Dennis SM (2009) Ovine genital actinobacillosis: A review. NZ Vet J 57 352–8. https://doi. org/10.1080/00480169.2009.64722. 112 Bruère AN, West DM, MacLachlan NJ et al. (1977) Genital infection of ram hoggets associated with a Gramnegative pleomorphic organism. NZ Vet J 25 191–3. https://doi.org/10.1080/00480169.1977.34401. 113 Baynes ID and Simmons GC (1968) Clinical and pathological studies of Border Leicester rams naturally infected with Actinobacillus seminis. Aust Vet J 44 339–43. https://doi.org/10.1111/j.1751-0813.1968.tb14399.x. 114 Watt DA, Bamford V and Nairn ME (1970) Actinobacillus seminis as a cause of polyarthritis and posthitis in sheep. Aust Vet J 46 515. https://doi. org/10.1111/j.1751-0813.1970.tb09190.x. 115 Foster G, Collins MD, Lawson PA et al. (1999) Actinobacillus seminis as a cause of abortion in a UK sheep flock. Vet Rec 144 479–80. https://doi.org/10.1136/ vr.144.17.479. 116 Angen Ø, Ahrens P, Kuhnert P et al. (2003) Proposal of Histophilus somni gen. Nov. sp. Nov. for the three species incertae sedis ‘Haemophilus somnus’, ‘Haemophilus agni’ and ‘Histophilus ovis’. Int J Syst Evol Microbiol 53 1449–59. https://doi.org/10.1099/ijs.0.02637-0. 117 Philbey AW, Glastonbury JR, Rothwell JT et al. (1991) Meningoencephalitis and other conditions associated with Histophilus ovis infection in sheep. Aust Vet J 68 387–90. https://doi.org/10.1111/j.1751-0813.1991.tb03104.x. 118 Walker RL and LeaMaster BR (1986) Prevalence of Histophilus ovis and Actinobacillus seminis in the genital tract of sheep. Am J Vet Res 47 1928–30. 119 Saunders VF, Reddacliff LA, Berg T et al. (2007) Multiplex PCR for the detection of Brucella ovis, Actinobacilus seminis and Histophilus somni in ram semen. Aust Vet J 85 72–7. https://doi.org/10.1111/j.1751-0813.2006.00098.x. 120 Constable PD and Webber JJ (1987) Escherichia coli epididymitis in rams. Aust Vet J 64 123. https://doi. org/10.1111/j.1751-0813.1987.tb09651.x. 121 Ladds PW (1993) The male genital system. In: Pathology of domestic animals, eds KVF Jubb, PC Kennedy and N Palmer. 4th ed. Vol. 3. Academic Press: New York and London, p. 471.

R e f e r e nc e s

122 Pulsford MF, Eastick BC, Clapp KH et al. (1967) Traumatic epididymitis of Dorset Horn and Poll Dorset rams. Aust Vet J 43 99–101. https://doi. org/10.1111/j.1751-0813.1967.tb08893.x. 123 Smith KC, Brown PJ, Barr FJ et al. (2012) Cryptorchidism in sheep: A clinical and abattoir survey in the United Kingdom. Open J Vet Med 2 281–4. https://doi. org/10.4236/ojvm.2012.24044. 124 Dolling CHS and Brooker MG (1964) Cryptorchism in Australian Merino sheep. Nature 203 49–50. https://doi. org/10.1038/203049a0. 125 Miller SJ and Moule GR (1954) Clinical observations on the reproductive organs of Merino rams in pastoral Queensland. Aust Vet J 30 353–63. https://doi. org/10.1111/j.1751-0813.1954.tb05398.x. 126 Gunn RMC, Sanders RN and Granger W (1942) Studies in fertility in sheep. Bull Coun Sci Industr Res Aust 148 111–15. 127 Watt DA (1978) Testicular pathology of Merino rams. Aust Vet J 54 473–8. https://doi.org/10.1111/j.1751-0813.1978. tb00291.x. 128 Dolling CHS (1970) Breeding Merinos. Rigby Australia: Adelaide. 129 Singh LB, Dolling CHS and Singh ON (1969) Inheritance of horns and occurrence of cryptorchism in indigenous,

130

131

132

133

134

135

141

Rambouillet and crossbred sheep in India. Aust J Exp Agric Anim Husb 9 262–6. https://doi.org/10.1071/EA9690262. Bruere AN (1970) Some clinical aspects of hypo-orchidism (small testes) in the ram. NZ Vet J 18 189–98. https://doi. org/10.1080/00480169.1970.33897. Underwood EJ and Somers M (1969) Studies of zinc nutrition in sheep I: The relation of zinc nutrition to growth, testicular development and spermatogenesis in young rams. Aust J Agric Res 20 889–97. https://doi. org/10.1071/AR9690889. Murray RM (1969) Scrotal abnormalities in rams in tropical Queensland with particular reference to ovine brucellosis and its control. Aust Vet J 45 63–7. https://doi. org/110.1111/j.1751-0813.1969.tb13691.x. Carr PM (1972) An apparently inherited inguinal hernia in the Merino ram. Aust Vet J 48 126–7. https://doi. org/10.1111/j.1751-0813.1972.tb02245.x. Williamson P and Nairn ME (1980) Lesions caused by Corynebacterium pseudotuberculosis in the scrotum of rams. Aust Vet J 56 496–8. https://doi. org/10.1111/j.1751-0813.1980.tb02565.x. Rhodes AP (1975) Seminal degeneration associated with chorioptic mange of the scrotum of rams. Aust Vet J 51 428. https://doi.org/10.1111/j.1751-0813.1975. tb15792.x.

chapter 6

REPRODUCTION 2 Ultrasound Scanning for Pregnancy

143

Tristan Jubb

6.1  THE APPLICATION OF ULTRASOUND PREGNANCY SCANNING ON SHEEP FARMS 6.1.1  Reasons for Scanning Ultrasound waves can be used in sheep to detect pregnancy and to count and age foetuses. This enables sheep owners to allocate ewes to mobs based on foetal number and provide differential management to increase productivity and profit. The potential benefits of ultrasound scanning for pregnancy are numerous and include: 1. Non-pregnant ewes can be identified, allowing early action to be taken to sell, re-join or run these ewes for wool production alone. 2. Non-pregnant versus single-bearing versus multiplebearing ewes can be identified for feeding according to need and to decide allocation to lambing paddocks. Each group has different nutritional requirements which, if not met, may result in poor productivity and compromised survival of both lambs and ewes. Pregnant ewes in poor body condition can be identified in time for targeted feeding to reduce the risks to productivity associated with undernutrition during pregnancy and lactation. 3. Multiple-bearing ewes can be identified to receive priority attention during pre-lambing husbandry events (such as vaccination, crutching, anthelmintic treatment and foot paring). These ewes in particular should not be yarded too close to lambing, kept off feed for extended periods or exposed to muddy yard conditions. 4. Multiple-bearing ewes can be allocated to suitably sheltered areas of the farm for lambing and at stocking densities that facilitate uninterrupted ewe–lamb bonding. This may be particularly important for litter sizes greater than two. 5. The extent and timing of reproduction losses can be revealed. Comparing scanning, lambing and lamb-marking data can help determine the separate contributions of ram fertility, ewe fertility, abortions and lamb survival to reproductive underperformance.

6. The factors influencing reproductive performance under different management conditions on a farm can be identified by comparing single-to-multiple ratios, non-pregnancy rates and distribution of conceptions between mobs and years. 7. Early- versus late-lambing ewes can be identified to graze and supervise separately. This enables farmers, busy during lambing, to focus supervision on one set of paddocks for a short period rather than numerous paddocks over an extended period. Nutritional demands are different between ewes that are early and late pregnant; therefore, if feed is short, the later-lambing ewes can be put under more nutritional pressure for a period. 8. The best lambing paddocks on the farm can be identified by knowing wastage between scanning and lamb marking occurring over time for different paddocks. 9. The lambs from single-, twin- or triplet-bearing ewes can be identified, from which to preferentially select replacement ewes. 10. In ram-breeding flocks, pregnancy scanning data may provide useful information for the calculation of reproduction-related ASBVs (Australian sheep breeding values).1 11. Pathological conditions affecting the flock such as dead or dying foetuses, pyometra, hydrometra, clover disease, ectopic pregnancies and uterine torsions can be identified. These can be diagnosed, treated and culled, and measures can be introduced to prevent recurrence. 12. Drying-off dates for milking sheep in dairy flocks can be identified. Economic analyses of profitability of scanning have used different assumptions, different benefits and different enterprises, and have drawn different conclusions. Returns as high as 400% have been calculated.2 Suffice to say that pregnancy scanning is a relatively low-cost procedure; there are numerous tangible and intangible benefits, and it will be profitable for most sheep producers when scanning for multiples. The returns to the producer from educational value alone are considerable.

DOI: 10.1201/9781003344346-6

144

CHAPTER 6: Reproduction 2: Ultrasound Scanning for Pregnancy

6.1.2  The Scanning Procedure Ultrasound waves are high-frequency inaudible sound waves. A  transducer, also known as a probe, transmits bursts of sound waves which pass through and are reflected differentially by tissues of different density at different distances. Between bursts, the probe captures returned sound waves which are converted into electrical impulses to generate a real-time, two-dimensional image in which fluid is black, bone is white and soft tissues are shades of grey. Lower-frequency waves penetrate more deeply into the body but provide poor image resolution; higher frequency waves do not penetrate as deeply but provide higher resolution. Ultrasound waves will not pass through air; therefore, the probe must have an airless contact with the body surface. A good contact is achieved by pumping a coupling liquid such as warm water or methylcellulose gel onto the face of the probe then lightly pressing the probe on to clean, hairless, wool-less skin. Wool, dirt, grease and faeces between the probe and skin, and overcrowding of the abdominal cavity with food, foetuses or fat causes scattering and dilution of ultrasound waves and degrades the image. Most commercial pregnancy scanning of sheep around the world is conducted transabdominally by nonveterinarians, and at the time of writing, most of them use the portable Ovi-Scan™ ultrasound scanner specifically designed for use in sheep. It has a wide 170° sector image and up to 32 cm depth of penetration and provides its most interpretable images at the 3.5 and 5.0 MHz settings. The Ovi-Scan™ can be integrated with a tally counter, electronic tag readers, drafting gate controllers and pumps for coupling liquids. Typically, the scanner sits on the left side of a standing sheep restrained in a narrow, walk-through crate (Figure 6.1). The handheld probe is passed behind and between the back legs and pressed onto the inguinal pocket, which is the bare abdominal skin of the right inguinal region above the udder. Placing the probe on the skin of the right inguinal pocket is preferred because the rumen, which is on the left side, pushes the gravid uterus to the right side adjacent to the pocket. Some scanners who use human medical scanning machines with narrow-angle probes prefer the sheep to be restrained in dorsal recumbency, enabling easier access to both inguinal pockets. To count and age foetuses accurately the probe is rotated in an arc so that the entire uterus is scanned from one end to the other. The wide sector angle causes the resolution to be less than that offered by the diagnostic ultrasound systems used in humans (and veterinary clinics); however, it allows the entire cross section of the uterus to be imaged with one placement of the probe. This reduces the chance

of counting foetuses twice and improves accuracy and speed. The probe must not move anteriorly off the bare skin on to the adjacent wooled or haired area or the image will be lost. Anchoring the probe by pinching a fold of loose inguinal skin to the side of the probe prevents this movement. It is a technique that scanners must learn to do well and requires considerable thumb and forefinger strength for scanning large numbers of sheep in one day. Directing the ultrasound waves caudally into the pelvic cavity is important to detect very early pregnancies. Directing the waves as far anteriorly as possible, which requires anchoring the probe, is important to detect advanced pregnancies. Confirmation of pregnancy is based on seeing uterine fluid, foetal structures and placentomes. At 26–30 days gestation there is slight fluid in the uterus surrounded by an irregular edge, but the embryo is not visible. At 35 days there is an identifiable small black pocket of amniotic fluid with a more pronounced irregular edge, which are the placentomes beginning to fold (evaginate), and a tiny, grey, jellybean-shaped embryo with limb buds becoming visible. By 40 days, foetuses are readily identifiable, the skull and ribs are white but not yet bright white, and the placentomes

Figure 6.1  Typically, a scanner sits on the left side of a walk-through crate passing the probe behind and between the ewe’s back legs to access the right inguinal pocket. Source: Lesley Abbott.

6 .1 Th e A ppl ic at ion of Ult r a sou n d P r e g n a nc y S c a n n i ng on Sh e e p Fa r m s

Figure 6.2  An ultrasound image of a cross section of a pregnant uterus showing black uterine fluid, a foetal skull and a hollow-centred, doughnut-like placentome. Source: Lesley Abbott.

are small grey C- and O-shaped structures. By 45 days the skull is bright white, specific foetal structures are identifiable, especially the ribs, and mature, hollow-centred, doughnut-like placentomes are clearly visible (Figure 6.2). As the pregnancy progresses through its early stages and the foetuses enlarge, other parts of the skeleton become brighter white, organ masses within the trunk become more discernible and movements of head and limbs are more easily noticed. As the foetuses enlarge and pass 80 days of gestation, there is a tipping point where the scattering and dilution of reflected ultrasound waves cause a rapid deterioration in image quality, especially for high litter sizes. This does not affect the accuracy of detection of pregnancy but does affect the accuracy of counting and ageing of foetuses.

6.1.3  Scanning Windows The term ‘scanning window’ refers to the preferred time after joining commences for scanning. For detecting pregnant versus non-pregnant ewes, a process referred to as wet/drying, the time-point preferred by experienced sheep scanners is to scan 42 days or more after the rams are removed through to a time 130 days after joining commenced. At less than 42 days, scanners must contend with small, difficult-to-access intrapelvic pregnancies, and if scanning conditions are less than ideal (fat, full or fidgety ewes or ewes with dirty inguinal pockets), it is easy to miss small pregnancies. Also, by 42 days, the highrisk period for early embryonic loss has passed. From 42 days to near term, pregnancies are usually instantly recognisable.

145

Experienced scanners try to avoid scanning within 3 weeks of lambing (>130 days gestation). Near-term pregnancies can be missed if located too far cranially and ventrally for the ultrasound waves to reach. This is particularly the situation in some deep-bellied ewes that have not been kept off feed (usually in an attempt to avoid metabolic diseasea) and consequently have tight abdominal skin, making it difficult to anchor the probe. Misdiagnosing these heavily pregnant ewes as dry can be disastrous, as they may subsequently be culled, deprived of food and water for transport to saleyards or abattoirs and, during the journey, succumb to pregnancy toxaemia. A non-gravid uterus normally does not contain enough fluid inside or around it to be made visible by ultrasound. Therefore, identifying non-pregnant ewes relies on uterine fluid, foetuses and placentomes not being found in the normal locational range of the uterus, including in the pelvic cavity. If exposure to a ram has occurred in the past 5 weeks, then an undetectable early-stage pregnancy may be present but missed. When the client wants single- and multiple-bearing ewes to be differentiated, a process referred to as twinning, the situation preferred by experienced sheep scanners is for the flock to be joined for 5–7 weeks, with scanning occurring 6 weeks after the rams are removedb. At this stage the pregnancies are in the 42–91 days twinning window; the entire uterus can still be scanned, and the quality of the images is sufficiently high to distinguish single from multiple pregnancies relatively quickly and easily. After 95 days the foetus grows rapidly and moves forward in the abdomen, making it increasingly difficult to scan through the entire uterus—an essential step for counting foetuses when there is more than one foetus in one uterine horn. For extended joining periods (≥8 weeks) and when the client requests twinning, most scanners prefer to scan at 84 days (after joining start) and rescan the undetectably pregnant ewes 6 weeks later. When the client wants triplet and greater litter sizes to be differentiated, a process known as tripletting, the situation preferred by experienced sheep scanners is for the ewes to be in the 42–75 days pregnancy range (the tripletting window). This requires scanning at 75 days after joining start but is problematic because it imposes the requirement of rescanning the undetectably pregnant ewes 2–3 weeks later if joining extends beyond 5 weeks. However, to avoid the  Hypoglycaemia, hypocalcaemia and pregnancy toxaemia.  To ‘twin’ the ewes means categorising all ewes bearing multiple foetuses as twin-bearing and not differentiating between those with two and those with three or more foetuses. To ‘triplet’ means to separately identify ewes with twins, ewes with triplets, ewes with quadruplets and so on. a

b

146

CHAPTER 6: Reproduction 2: Ultrasound Scanning for Pregnancy

cost of a return visit to rescan a smaller number of sheep, tripletting is often attempted when ewes are in the less than ideal 42–84 days or 42–91 days gestation range. The consequence is a reduction in accuracy for detecting triplets. Some very capable scanners (and their clients) claim their accuracy is high for twinning and tripletting in the 35–100 days pregnancy range, but this is the exception. Such scanners are vastly experienced and are very competent individuals who typically scan hundreds of thousands of ewes annually and have the ability to interpret incomplete or poorer-quality images rapidly and accurately.

6.1.4  Counting Foetuses There are many ‘tricks’ that sheep scanners use to help count foetuses when image quality is poor and only parts of a foetus are recognisable. Here are some examples: • A relatively large number and density of placentomes is always a good clue that more than one foetus is present. • Independent foetal movements can be stimulated by irritating the foetus with ultrasound waves aimed at it for several seconds or by sharply balloting the abdomen with the probe hand. • The opening of the C of the C–shaped placentomes faces toward the foetus it is supplying, so that if placentomes are back-to-back facing in opposite directions, it is likely there are at least two foetuses. • The orientation of the foetal skull, which resembles a bird’s head with a beak, shows the direction it is facing and therefore where its trunk and legs should be. If a trunk or legs are seen somewhere else, then another foetus is likely to be present. The orientation of a set of ribs or spine can be used similarly. • The image of the ribs in cross section resembles a squadron of planes flying in V-formation toward the foetus’s head, so that if a bright white head is located toward the rear of the formation, it must belong to another foetus. • Gauging the age of the foetus from head or trunk diameter then matching the arc of rotation of the probe to the expected length of the foetuses (which can range from 2 cm at 40 days to 20 cm at 100 days) can help decide if one or two foetuses are present. This is an important skill when multiple foetuses occupy one horn.

6.1.5  Foetal Ageing Requests for foetal ageing are usually made for the purposes of identifying conceptions to set-time artificial insemination (AI) versus back-up rams and for determining

lambing dates for close supervision of ewes at lambing. For the latter, the most common request by the producer is foetal ageing in order to segregate ewes that were joined for 5 or 6 weeks into two groups that each lamb in a 2or 3-week period. Experienced sheep scanners are often confident in being nearly 100% accurate with the 3-week batches but less so with 2-week batches because, after 70 days, genetic differences in growth rate between individual foetuses affect size-for-age. Requests for accurate ageing >90 days post joining start should be resisted because of poor image quality and the overlapping size ranges of foetuses of the same age. On the Ovi-Scan™ device there are trunk diameter reference circles at the top corners and short lines at the bottom of the screen for the 56–91 days pregnancy range to assist with foetal ageing. Prior to foetal ageing of a mob, experienced scanners will calibrate themselves on 50 or more ewes from the mob by comparing trunk and skull diameters with the circles. In AI programmes, back-up rams are usually introduced 14 days post AI to cover non-pregnant ewes which return to oestrus at around 17 days (and again around 35 d) post AI. Experienced scanners typically try to scan in the range 65–84 days post AI because this is the period that gives the clearest differentiation between conceptions to AI and back-up rams. The choice of when in this range to scan is decided by a compromise between the need to triplet the AI pregnancies, the need to detect and count pregnancies to a second oestrus cycle (35 days post AI) with back-up rams and the urgency with which the client wants to know the results of his or her expensive AI programme. For example, scanning at 80–84 days post AI prevents accurate tripletting of AI conceptions but allows accurate detection and counting of conceptions to secondcycle back-up rams, whereas scanning at 65–75 days allows accurate tripletting of the AI conceptions but reduces the accuracy of detection and counting of conceptions for the second-cycle back-up rams.

6.1.6  The Rate of Scanning The number of ewes able to be scanned per hour varies greatly. In walk-through scanning systems, with an experienced scanner operating under optimal scanning conditions, normally it takes just a second or two for the sheep to be encouraged into the scanning crate, then a few seconds while the sheep is detained for the scanner to position the probe, pump water onto the face of the probe, make a good air-free contact, anchor the probe, scan through the uterus from one end to the other, interpret the image and press the tally counter button. Then normally it takes just a second or two for the sheep to exit the crate.

6 . 2 Th e R e l i a bi l i t y a n d A c c u r ac y of Ult r a sou n d S c a n n i ng f or P r e g n a nc y

Counting and ageing foetuses at rates of 250–350 sheep/ hr and wet/drying rates exceeding 400 sheep/hr are routinely achieved by experienced scanners under the most commonly encountered commercial conditions. Some highly experienced scanners can achieve rates double these. They typically have enhanced walk-through, pneumatic handling systems including squeeze restraints and are insistent on operating only under optimal scanning conditions. However, even the most experienced scanners using the most sophisticated systems can be slowed to rates of 50 sheep/hr if image quality is poor, which can occur if the ewes are fat, fidgety or full; were recently fed hay or silage; have dirty inguinal pockets; or if scanning is occurring outside the optimal scanning window.

6.1.7  Pathological Diagnoses There are several pathological diagnoses that can be made by the scanner. He or she may observe ‘bunches of grapes’, which are the endometrial cysts of chronic phyto-oestrogen toxicity (ie clover disease). A  pregnancy rate which is lower in older age groups than in younger ewes is also a characteristic of clover disease. A hydrometra image appears as multiple well-defined, round, black holes which at necropsy are coiled fluid-filled, thin-walled uterine horns where the remnants of placentomes can be seen. Hydrometra can follow the death of an embryo or early foetus, and some workers have observed an association between a high incidence of hydrometra and joining on actively growing lucerne and an association with heat waves during early pregnancy. A foetus that has died but not become mummified is still readily detectable by ultrasound, but it is usually only very experienced scanners who recognise that the foetus is dead during routine (high-throughput) pregnancy scanning. The foetus and placentomes are less defined than normal, foetal movements cannot be stimulated and a heartbeat cannot be detected. These are also features of a poor-quality image of a live foetus and are therefore often mis-diagnosed as a live foetus. Dead foetuses can be visualised as long as there is still fluid surrounding the foetus in the uterus. Mummified foetuses are difficult to detect because they are not surrounded by fluid. The large and partially mummified dead lambs of ectopic pregnancies and long-standing uterine torsions are not normally recognised by ultrasound because the uterine fluid has been resorbed. They are usually detected by the bony lumps balloted through the abdominal wall when placing the probe. Chronic mastitis and abdominal hernias can be detected by the scanner as the probe is placed. The characteristic smells of footrot, necrotic skin cancers and flystrike alert the scanner to the presence of these

147

diseases and are relevant to the reproductive investigation underway—these are amongst the conditions which can contribute to a reduction in fertility.

6.2  THE RELIABILITY AND ACCURACY OF ULTRASOUND SCANNING FOR PREGNANCY 6.2.1  Experienced Scanners and Good Conditions of Scanning Amongst those working in the field of ultrasound scanning of ewes it is generally agreed that an experienced scanner is a person who: • has passed a 4- or 5-day intensive hands-on training course with lots of practical time and one-on-one instruction from an experienced instructor, learning to manipulate the probe and to interpret a real-time twodimensional image, and • has gained further experience performing at least 100,000 scans over the subsequent 2–3 years, counting and ageing foetuses in a wide range of commercial settings, and • maintains his or her skills by scanning >10,000 ewes annually. It is these three conditions that provide the definition of an experienced scanner which will be used in the later discussion on scanning accuracy. It is only when these three conditions are met that a scanner can deliver near 100% accuracy under good scanning conditions. Most experienced scanners will recall learning to scan as one of the most difficult and stressful periods of their lives, littered with embarrassingly slow, error-ridden jobs and dissatisfied customers.

6.2.1.1  Good Conditions of Scanning Scanners, whether novice or experienced, know when conditions allow them to deliver high accuracy and when they are making informed but uncertain decisions about the pregnancy status of ewes. The generally agreed good conditions of scanning, which allow an experienced scanner to deliver very high accuracy for detecting, counting and ageing foetuses, are as follows: 1. When the ewes are between 42 and 135 days for wet/ drying, 42–91 days for twinning and ageing, 42–75 days for tripletting and quadrupletting and 65–84 days for AI conceptions when back-up rams are introduced 14 days later. 2. The ewes are not overly fat, fidgety or full. Ewes that are overly fat often provide poor image quality because

148

CHAPTER 6: REPRoduCTion 2: ulTRASound SCAnning FoR PREgnAnCy

the ultrasound waves must pass through the omentum, which, in fat ewes, extends into the caudal abdomen of the right side where the probe is placed. Ewes that are fidgety and move excessively make it difficult to anchor the probe to scan through the uterus and study the image adequately. Ewes that are overly full are those not kept off feed for 12 hr and not kept off hay and silage for 3 days before scanning. Scattering of echoing waves by food in the gastro-intestinal tract and distortion and displacement of the uterus by a full rumen contribute to poor image quality, and tightness of the abdominal skin prevents anchoring of the probe. 3. There are sufficient people to make the sheep flow steadily through the scanning crate and to steady any struggling or fidgety ewes and stand any ewes which kneel or lie in the crate. Struggling or fidgety ewes and ewes that kneel or lie down in the scanning crate affect scanning accuracy by preventing proper placement of the probe, shorten the time to study the image and contribute significantly to operator fatigue. 4. The scanner can take regular rest breaks so as not to become overly fatigued. The scanner and the scanning equipment are protected from dust and extremes of weather. Fatigue and distractions lead to rushing and poor probe placement, in turn leading to poor image quality and insufficient time allocated to scanning from one end of the uterus to the other and properly studying the poorer-quality image.

6.2.2 Understanding the Discrepancy between Scanning and Lambing Results There is commonly a discrepancy between the number of foetuses counted at scanning and the number of lambs (live and dead) counted at lambing and lamb marking. The discrepancy is a result of several factors and not simply diagnostic errors made by the scanner. The other factors are often overlooked by sheep producers and some authors in the published literature1,3,4,5,6,7 Understanding the reasons for any discrepancy will help veterinarians who are conducting reproductive investigations avoid misappropriation of blame and help them give correct advice to producers on the conditions required to minimise discrepancies.

6.2.2.1 Expected Level of Accuracy When the ewes are presented for scanning correctly and in good conditions, with pregnancies in the optimum scanning window, the accuracies achieved by a competent scanner are expected to be very high, particularly for wet/drying and identification of multiples versus singles (Table 6.1).

6.2.2.2 Sources of Error The factors—or sources of error—that contribute to discrepancies between scanning numbers and the number of live lambs at birth or at marking can be categorised under four headings: 6.2.2.2.1 Errors in Recognising Foetal Number When working under good conditions and in the optimum scanning window, errors by the scanner when scanning multiples are predominantly due to misallocating single- and twin-bearing ewes. Errors in tripletting are predominantly errors in allocation between twin- and triplet-bearing ewes. When the scanning conditions are not good or the ewes are scanned outside the most appropriate scanning window, errors in detection of foetuses or in identifying the correct number of foetuses are more likely to occur and accuracies will fall below those shown in Table 6.1. 6.2.2.2.2 Errors in Identification After scanning, ewes must be correctly identified on the basis of their pregnancy status and, if drafted into separate groups for lambing, maintained separately. Errors of identification can be due to mis-drafting, loss of ear tags, faded spray marks, straying of individual or small numbers of ewes through fences into other mobs, accidental boxing of mobs when gates are left open, unrecorded deaths and other unforeseen events that occur in the subsequent 4 months before lambing is completed. Incomplete musters (when the ewes are not presented for scanning but they and their lambs are counted at lambing) also fall into this category. 6.2.2.2.3 Foetal Losses after Scanning A significant proportion of foetuses are lost between scanning and lambing. The cause of foetal loss may be

Table 6.1 The Expected Accuracy of Scanning for Pregnancy and Foetal Number When Performed by a Competent Scanner Working in Good Scanning Conditions OBJECTIVE OF SCANNING WET/ DRYING

TWINNING TRIPLETTING AGEING INTO TWO GROUPS

Preferred joining duration

Any

35–49 days

Optimum scanning window

42–130 42–91 42–75 days days days gestation gestation gestation

42–91 days gestation

Accuracy

~99–100% ~98%

~90%

35 days (or re-scanning if longer)

~95%

35–49 days

6 . 2 Th e R e l i a bi l i t y a n d A c c u r ac y of Ult r a sou n d S c a n n i ng f or P r e g n a nc y

deficiencies of maternal serum progesterone,8 placental insufficiency 9 or abortions due to infectious agents or other abortifacients such as onion grass. In the absence of pathogenic agents, foetal losses of 20% are not unexpected8,10 In the case of progesterone deficiency or placental insufficiency, foetal losses can be partial or complete losses, ewes with multiples usually losing one but not all foetuses. Such losses can occur at any stage of gestation.8 The number of foetuses lost per 100 ewes increases with increasing ovulation rate—so foetal loss error is greater in flocks of ewes of high fecundity compared to low-fecundity flocks. In the case of the pathogenic agents, it is also most likely that the loss of the pregnancy will involve all foetuses. In Australia, ewes are normally run under extensive conditions, and most aborted foetuses are never detected by the flock manager; if some are observed, accurate counts are very unlikely. 6.2.2.2.4 Counting Errors after Birth (Providing a Benchmark for Calculations) These errors are a consequence of imperfect methods of counting the number of lambs born. For example, if newborn lambs are counted in the paddock, some may have been removed by predators before counting.4,6 Crossfostering can go unnoticed, particularly overnight, confusing attempts to reconcile multiple lambs to a particular ewe. Even with twice-daily paddock inspections, if paddocks are inspected a 9 am and 4 pm each day, 7–17 hours can pass between inspections. There may also be differences in the diligence between researchers and farmers with respect to the skill and thoroughness of inspections and recording findings. With birth-counting systems indoors, sometimes producers may only record the number of live lambs.6 Attempts to reconcile foetal numbers detected at scanning with lamb-marking numbers (when lambs are 2–8 weeks old) are even more hazardous. Under normal circumstances, most lamb mortalities before marking occur in the perinatal period, but the level of mortality is rarely known with any accuracy under extensive grazing conditions. Rates of loss of single-born lambs often exceed 10% and of multiple-born lambs 20%, even under good management systems, but rates can be very much higher at times. Even in experimental work, when scanned-pregnant ewes are slaughtered and foetuses counted, errors are still possible. While it would be expected that such an approach would be the gold standard for estimating foetal number, in busy, high-throughput abattoir environments the potential for recording errors remains high. Errors can occur in the identification of ewes, retrieval of uteri and finding and counting sometimes small, multiple foetuses.

6.2.3

149

Measures of Accuracy

There are three measures of accuracy used to describe scanning error. The first is accuracy of prediction, equivalent to the predictive valuec of a test and a measure of the scanner’s ability to predict pregnancy status (when wet/ drying) or litter size (when twinning or tripletting). The second is accuracy of detection, which is equivalent to the sensitivity and specificity of a test.d This is a measure of the scanner’s ability to detect all the ewes with a specific pregnancy status or litter size. The third is overall accuracy, which is a combination of the first two. These measures can be explained by a two-by-two contingency table (Table 6.2). A worked example for a flock of 1000 ewes that were wet/dried at scanning is shown in Table 6.3. In the example in Table 6.3, the accuracy of prediction for ewes scanned pregnant and ewes scanned empty is 99% and 90% respectively; the accuracy of detection of pregnant ewes and empty ewes is 99% and 95% respectively, and the overall accuracy is 98.5%. Measures of the accuracy of scanning can also be applied to the identification of ewes with a specified litter size. In practice, usually only positive predictive values and sensitivities are required to describe accuracy. As an example, Table  6.4 contains data from a flock in which the lambs were counted at birth. The discrepancies between scanning and lambing numbers are due to the full combination of error categories—ie, scanning errors, identification,

Table 6.2 A Contingency Table Showing the Derivation of the Terms Used to Describe the Accuracy of Ultrasound Scanning for Pregnancy ACTUAL STATUS TEST RESULT

POSITIVE

NEGATIVE

Positive

A True positive

B False positive

Negative

C False negative

D Negative predictive True negative value (NPV) = D/(C+D)

Sensitivity (Se) Specificity (Sp) = A/(A+C) = D/(B+D)

Positive predictive value (PPV) = A/(A+B)

Overall accuracy (OAA) = A+D/(A+B+C+D)

  The ratio of patients truly diagnosed as positive to all those who had positive test results. d The proportion of patients with the condition that test positive. c

150

CHAPTER 6: REPRoduCTion 2: ulTRASound SCAnning FoR PREgnAnCy

foetal loss and lamb-counting errors. This example illustrates the results that might be expected under normal commercial-farming conditions with experienced and competent scanners and sheep flock managers.

Table 6.3 A Contingency Table Displaying an Example of the Calculation of Accuracy of Prediction, Accuracy of Detection and Overall Accuracy for a Flock of 1000 Ewes Scanned for Wet/Dry Status ACTUAL PREGNANCY STATUS SCANNING DIAGNOSIS Pregnant Empty

6.2.4

PREGNANT

EMPTY

895

5

PPV = 99%

10

90

NPV = 90%

Sensitivity =  99%

Specificity =  95%

OAA = 98.5%

Studies of Scanning Accuracy

The accuracies of scanning from 10 studies reported in six publications are summarised in Table  6.5.1,3–7 Predictive accuracy (PPV) and, in some cases, detection accuracy (Se) for litter size were presented or could be calculated in these reports. Studies identified as numbers 1, 3, 4 and 7–10 in Table 6.5 were conducted in Australia, and studies 2, 5 and 6 were conducted in Europe.

Table 6.4 A Contingency Table Displaying an Example of the Calculation of Accuracy of Prediction (Predictive Values), Accuracy of Detection (Sensitivities) and Overall Accuracy for A Flock of 1000 Ewes Scanned for Litter Size Status LITTER SIZE AT LAMBING SCANNING DIAGNOSES

0

1

2

≥3

TOTAL

Positive predictive values

0

268

3

4

0

275

97.5%

1

0

902

18

1

921

97.9%

2

3

134

1423

7

1567

90.8%

≥3

0

4

6

186

196

94.9%

271

1043

1451

194

2959

Overall accuracy 93.9%

98.9%

86.5%

98.1%

95.9%

Total Sensitivities

As described earlier, the PPV and Se values must be interpreted with caution because the relative contributions of scanner diagnostic error versus other sources of error are, in almost all cases, not known. The contribution of scanner diagnostic error to misclassification may only be minor. In only two studies4,6 was the presence of errors other than scanner error acknowledged. Despite the limitations, the values in Table 6.5 provide an indication of the range of misclassification which can occur. Misclassification is important because the nutritional management of ewes after classification is normally made appropriate for their status—non-pregnant ewes receiving lower levels of nutrition than pregnant ewes and multiple-bearing ewes receiving the best pastures and, if necessary, supplements. In each case in Table  6.5, the PPV indicates the proportion of ewes in a mob, be it a dry, single, twin or triplet mob, that will be managed appropriately for their nutritional needs. The Se values indicate the proportion of ewes

of a certain litter size that will be managed correctly (or incorrectly). It can be deduced from the authorships, year and methodologies in the reports that the scanning in studies numbered 1–4 in Table 6.5 was probably performed with human medical ultrasound machines operated by scientists under research conditions, while in studies 5–10 it was probably performed by experienced scanners using wide-angle OviScan™ machines operating under commercial conditions. In at least five studies (studies 1, 5–7, 10) gestational ranges were such that a significant proportion of pregnancies would have been outside the optimal detection, twinning or tripletting windows. In other words, good conditions of scanning were not present, making a proportion of foetuses undetectable or uncountable. In studies 4 and 5, accuracies were not calculated for ewes scanned as non-pregnant because most were culled soon after scanning. Failure to follow-up ewes scanned as non-pregnant affects estimates of accuracy because these ewes may in fact

6 . 2 Th e R e l i a bi l i t y a n d A c c u r ac y of Ult r a sou n d S c a n n i ng f or P r e g n a nc y

151

Table 6.5 Accuracy of Prediction (PPV) and Detection (Se) in Studies Measuring Scanning Error (nd = no data) SCANNED NUMBER STUDY (RESTRAINT, DURATION OF PROCEDURE, BENCHMARK)

3

≥3

4

≥4

NO. SCANS

0

1

1. Fowler & Wilkins (1984) (dorsal in cradle, 1 minute, foetuses counted at slaughter)

PPV (%)

93.9

97.7 97.1 82.1 –

0.0 –

Se (%)

99.8

98.6 93.8 52.3 –

0.0 –

2. Taverne et al (1985) (standing in crate, 2–3 minutes, lambs counted by farmers and researchers)

PPV (%)

nd

84.1 76.4 –

91.9 –

–

Se (%)

nd

89.8 86.6 –

59.6 –

–

3. Smith et al (1988) Flocks 1–2 (unknown, unknown, foetuses counted at slaughter)

PPV (%)

99.2

98.6 92.0 –

73.1 –

4. Smith et al (1988) Flocks 3–5 (unknown, unknown, lambs counted by researchers)

PPV (%)

100.0 93.0 84.2 –

68.8 –

5. Fridlund et al (2013) (standing in crate, 10–15 seconds, lambs counted by farmer)

PPV (%)

nd

93.7 91.9 82.4 –

–

70.8 1–131

6. Schmid et al (2016) (standing in crate, 30 seconds, lambs counted by farmer)

PPV (%)

82.8

89.9 93.8 95.6 –

–

–

26–110

853

7. Bunter et al (2016) Flock 1 (standing in crate, 10–30 seconds, lambs counted by farmer)

PPV (%)

97.5

97.9 90.8 –

94.9 –

–

69–93

2959

Se (%)

98.9

86.5 98.1 –

95.9 –

–

8. Bunter et al (2016) Flock 2 (standing in crate, 10–30 seconds, lambs counted by research team)

PPV (%)

93.7

94.3 89.0 –

6.3

–

–

unknown

9512

Se (%)

92.8

94.6 90.0 –

3.4

–

–

9. Bunter et al (2016) Flock 3 (standing in crate, 10–30 seconds, lambs counted by research team)

PPV (%)

98.6

96.1 86.4 –

14.3 –

–

unknown

12,708

Se (%)

91.0

98.1 85.6 –

12.5 –

–

10. Bunter et al (2016) Flock 4 (standing in crate, 10–30 seconds, lambs counted by farmer)

PPV (%)

96.5

82.3 82.0 –

80.6 –

–

2–109

10,776

SSe (%)

77.4

86.0 93.0 –

77.5 –

–

have been early pregnant (135 d) and therefore not detected to be pregnant at scanning. Ewes of induced high fecundity (study 2) or natural high fecundity (studies 1, 3, 5, 6, 7, 10) (and therefore predisposed to greater foetal loss) were used in 8 of the 10 studies. In studies 1 and 3, the foetal number used as a benchmark was provided by examination of uterine contents at slaughter immediately after scanning. The details of tracking and retrieving uteri, and then counting foetuses, were not described. The benchmark in the other studies was based on counts of lambs at lambing by the flock manager (studies 2, 5–7, 10) or a researcher (studies 2, 4, 8–9). It should be noted that, despite the suboptimal times of scanning, potential for foetal losses and imperfect benchmarks, there were still examples of very high accuracy.

2

STAGE OF GESTATION (DAYS) 40–47, 56–68, 83–96, 40–106

5530

45–77

210

–

50

269

–

80

842

39,664

6.2.5 Accuracy of Scanning for Ageing Foetuses The definitive study on accuracy of ageing of foetuses is by Schmid et al (2016)7 in Switzerland where an OviScan™ operated by an experienced Welsh scanner was used. In 781 ewes with a range of gestations at scanning of 26–110 days, the date of lambing was used to calculate the stage of gestation at scanning, which was then compared to the age of the foetus at scanning estimated by the scanner. It is presumed that the trunk diameter reference circles and lines on the Ovi-Scan™ screen were used to assist foetal ageing. The mean differences between the effective (calculated retrospectively after birth) and the estimated day of gestation are shown in Table 6.6.

152

CHAPTER 6: REPRoduCTion 2: ulTRASound SCAnning FoR PREgnAnCy

Table 6.6 The Mean Differences between the Effective and the Estimated Day of Gestation of 781 Ewes Scanned for Pregnancy with Foetal Age Estimated by the Scanner STAGE OF GESTATION (DAYS)

MEAN DIFFERENCE ± SD (DAYS)

26–110

5.6 ± 5.0

26–44

4.0 ± 4.9

45–90

5.2 ± 4.4

91–110

8.9 ± 6.4

Source: Schmid et al (2016)7

In that study, in the case of 134 ewes, foetal age was overestimated. In 40, the estimated and effective foetal age were equal, and in 607 ewes, foetal age was underestimated. • Amongst the 134 ewes where foetal age was overestimated, in 89%, 6% and 5% the difference was 1–10 days, 11–20 days and 21–30 days, respectively. • Amongst the 607 ewes where foetal age was underestimated, there were 89%, 9%, 0.7% and 0.7% in which the difference was 1–10 days, 11–20 days, 21–30 days and >30 days, respectively. The correlation between estimated and calculated foetal age was high (r = 0.936, P