Gastrointestinal Nematodes of Sheep and Cattle: Biology and Control

Foreword ix

Preface xi

Acknowledgements xiii

1 Nematode parasites 1

The nematodes 1

The important nematode genera and species parasitizing ruminant livestock 2

Abomasal genera 3

Small intestinal genera 4

Large intestinal genera 6

Nematode evolution 6

The transition to parasitism 8

Nematode biology 9

Nematode genetics 14

Nematode physiology 15

The dauer larva 17

Anhydrobiosis 17

The nematode life cycle 18

Niches occupied by parasitic nematodes within the vertebrate host 23

The lifespan of parasitic nematodes 26

2 Pathophysiology of nematode infections 33

Are parasites always harmful? 33

Defi ning ‘harm’ 34

The abomasum 36

The small intestine 42

The large intestine 43

The impact of parasites on overall gut function 43

Effects beyond the gut 47

3 Epidemiology of gastrointestinal nematodes in grazing ruminants 61

Ecology of GINs – pasture 61

Egg to L3 development 62

Effect of host 63

Survival of L3 63

Translation of infective larvae 64

Grazing behaviour and the avoidance of parasites 65

Patterns of infection 66

Overdispersion of parasites 67

Epidemiology of ‘parasitism’ 67

An increase in the infective mass 68

Alteration in the susceptibility of stock 69

Arrested development and hypobiosis 70

Introduction of susceptible stock onto an infected area 70

Insuffi cient age-related immunity 71

The introduction of infected stock to a clean environment 71

Epidemiology of cattle parasites 72

Population biology in the parasitic phase 72

Sheep parasites 73

Cattle parasites 75

4 The principles of gastrointestinal nematode control 83

Control of parasites with anthelmintic drenches 83

Drench programmes 84

Strategic drenching programmes 85

Principles of worm control in cattle 88

Control of GIN by grazing management 88

Alternate/mixed grazing with different host species or stock classes 89

Resistance to treatment 91

5 Anthelmintics 95

What are anthelmintics? 96

How effective does an anthelmintic have to be? 96

Which species does an anthelmintic against GIN need to remove? 97

Description, effi cacy, profi le and mode of action of anthelmintic families 98

Combination of anthelmintic treatments 107

Modifying the delivery of anthelmintics 107

Parenteral administration 108

Controlled release of anthelmintics 108

Injectable formulations 109

6 Anthelmintic resistance 117

Evolution of anthelmintic resistance 118

Worldwide occurrence of anthelmintic resistance 118

Resistance to one or more active families by one or more species 119

Impact of resistance on productivity 120

Mechanisms of resistance 120

Inheritance of resistance 123

Detection of resistance 124

7 Drenching and resistance 133

Frequency of treatment 134

Under-dosing 134

Persistent anthelmintics 135

Why use persistent drenches? 137

The provision of safe pasture and resistance 137

Persistence and effi cacy 138

Therapeutic effi cacy and resistance – ‘head selection’ 139

Prophylactic effi cacy and resistance – ‘tail selection’ 140

Heads or tails? 141

Persistent activity, immunity and resistance 142

Persistent activity, density dependence and resistance 143

Drench rotation 143

Controlling resistance by drench rotation 143

Drench rotation within seasons 145

Modelling drench rotation 145

Combination anthelmintics 146

Removing resistant worm burdens 146

Effi cacy of single actives vs. combinations 146

The odds are against multiple mutations 147

Resistance is already present to one or more constituent active 148

8 Worm control and resistance management 153

What is refugia? 155

Why do we need refugia? 155

How to produce and utilise refugia 157

Importation of resistant parasites 159

A twin approach to worm control and resistance management – utilising refugia and combination drenches 160

9 ‘Non-chemical’ control options 163

Anthelmintic plants 163

Plant material 165

Plant extracts 166

PSM as anthelmintics 167

Forage legumes 168

Practical applicability on-farm 169

Other anthelmintic plants 170

Micro-predacious fungi 170

Homoeopathy 171

10 Nutrition and parasitism 177

Metabolic cost of parasitism 177

Metabolic cost of infection 178

Metabolic costs of immunity 180

Parasites and nutrition: a nutrient utilisation framework 183

Supplementation for increased resilience to parasites 184

Supplementation for increased resistance to parasites 185

Reproducing animals 185

Undernutrition and parasitism 186

Micronutrients and parasitism 187

Improving nutrient availability 188

Forage plants and parasitism 188

Supplementation and immunity: increasing or enabling? 189

11 Animal genetics and parasitism 195

Inter-species variability 195

Inter-breed variability 196

Intra-breed variability 198

Resistance vs. productivity 199

Resilience 200

Pasture contamination, resistance and resilience 201

Markers for resistance and resilience 201

Phenotypic markers 202

Genotypic markers 203

Genetics, worm control and resistance management 204

12 The immune response to parasites 211

Evolution of the host–parasite relationship 212

Immunity and GIN population dynamics 213

The immune phenotype 214

Immunological unresponsiveness 214

Components of host responses to GI parasites 215

Adaptive immune responses to GINs 218

The anti-GIN immune response in cattle to O. ostertagi 221

Impact of immunity on parasites 222

Immunopathology 223

Periparturient rise 223

Utilising immune responses to control GIN 223

Natural antigens 224

Hidden antigens 225

What next for immunoparasitology research? 226

Postscript 235

Index 237