Equine Science

Zoe Davies is one of only a handful of qualified and Registered Equine Nutritionists in the UK. A former lecturer and external examiner in Equine Science, Zoe is a referral nutritionist, specialising in bloodstock and performance horses.

Preface xxiii

Acknowledgement xxv

1 The Biochemical Nature of Cells 1

Metabolism 1

Water 1

Important Properties ofWater 4

Proteins 4

Basic Structure of Amino Acids 4

Polypeptides 5

Levels of Protein Structure 5

Primary Structure of Proteins (Amino Acid Sequence) 6

Secondary Structure of Proteins (Alpha Helix or Beta Pleated Sheet) 6

Tertiary Structure of Proteins (3D Shape/Folding) 7

Quaternary Structure of Proteins (Aggregations of Polypeptide Chains) 7

Classification of Proteins 7

Structure of Collagen 8

Modification of Proteins 8

Denaturation of Proteins 8

Carbohydrates 8

Fructans 9

Starch 10

Cellulose 11

Glycogen 11

Lipids/Fats 11

Triglycerides 12

Essential Fatty Acids 12

Phospholipids 13

Cholesterol 15

Nucleic Acids 15

Deoxyribonucleic Acid (DNA) 15

Ribonucleic Acid (RNA) 16

Messenger RNA (mRNA) 17

Transfer RNA (tRNA) 18

Ribosomal RNA (rRNA) 18

Protein Synthesis 18

Transcription 18

Translation 20

The Genetic Code 21

Reading the Genetic Code 23

Enzymes 23

Factors that Affect the Activity of Enzymes 25

Temperature 25

pH 25

Enzyme Concentration 25

Substrate Concentration 25

Cofactors and Coenzymes 25

Enzyme Inhibitors 25

Metabolic Poisons 26

Drugs 26

Summary Points 26

Q + A 27

2 Cells, Tissues and Organs 29

Cells – Building Blocks of Life 29

Prokaryotic Cells 29

Eukaryotic Cells 31

Cell Function 31

Cytoplasm 32

Cytosol 32

Movement of Substances in and around Cells 32

Cell Organelles 32

Cytoskeleton 32

Cell or Plasma Membrane 33

The Fluid Mosaic Model of Cell Membrane Structure 34

The Role of Membranes in Cell Organelles 34

Nucleus 37

Endoplasmic Reticulum and Ribosomes 38

Golgi Body (Dictyosome) 38

Mitochondria 38

Lysosomes 38

Peroxisomes (Microbodies) 39

Centrosomes 39

Apoptosis (Programmed Cell Death) 39

Cell Turnover 40

Cell Division (Mitosis and Meiosis) 40

The Cell Cycle 40

Mitosis 41

Key Events 41

Cytokinesis or Cytoplasmic Division 43

Meiosis 44

Key Events 45

First Meiotic Division 46

Second Meiotic Division 46

Cell Signalling 46

Cell Differentiation and Stem Cells 46

Blood Cell Production from Stem Cells 47

Tissues and Organs 47

Epithelium/Epithelial Tissue 48

Epithelial Cell Shapes 50

Epithelial Arrangement of Cells 50

Connective Tissue 51

Connective Tissue Cells 52

Connective Tissue Fibres 52

Tissue Repair 53

The Four Stages ofWound Healing 54

Stage 1 – Traumatic Inflammatory Phase 54

Stage 2 – Destructive Phase (0–3 Days) 54

Stage 3 – Proliferative Phase (3–24 Days) 55

Stage 4 – Maturation Phase (24 Days to 2 Years) 56

Ageing Tissue 56

Stem Cell Therapy 56

Summary Points 57

Q + A 58

3 Equine Support and Movement 59

Points of the Horse 59

The Skeletal System 59

Bone 59

Classification of Bone Tissue 60

Dense or Compact Bone 60

Spongy or Cancellous Bone 61

Types of Bones 61

Microscopic Bone Structure 64

Bone Formation and Growth 64

Developmental Orthopaedic Disease 67

Bone Remodelling 68

Hormones and their Effect on Bone Growth 68

Effect of Exercise on Bone Tissue 69

Calcium Homeostasis 69

Bone Fracture and Repair 69

The Skeleton 70

The Axial Skeleton 70

The Skull 70

The Vertebral Column or Spine 71

The Appendicular Skeleton 75

Forelimb 76

Hindlimb 79

Stay Apparatus 80

The Mechanics of Movement 80

Joints 80

Types of Joints 81

Movement of Joints 83

Ageing of Joints 83

Muscles 83

CardiacMuscle 84

Smooth Muscle 84

Skeletal Muscle (Voluntary or Striated Muscle) 85

The Sliding FilamentModel 87

Muscle Anatomy 87

Muscles of the Neck and Shoulder 91

Brachiocephalic 91

Sternocephalic 91

Splenius 91

Trapezius 91

Rhomboideus 95

Deltoideus 95

Triceps 95

Muscles of the Trunk 95

Latissimus Dorsi 95

Pectorals 95

Muscles of the Forearm 95

Digital Extensor 95

Digital Flexor 95

Muscles of the Abdomen 97

Intercostal Muscles 97

Longissimus Dorsi 97

Muscles of the Hindlimb 97

Gluteal 97

Biceps Femoris 97

Semitendinosus 97

Digital Extensor 97

Gastrocnemius 99

The Importance of Muscle Fibres in Equine Performance 99

Muscle Fibre Types 99

Muscle Fibre Recruitment 100

Fatigue 101

Causes of Fatigue 101

Lactic Acid Accumulation 101

Summary Points 101

Q + A 101

4 TheLowerLimb 103

Tendons and Ligaments of the Lower Limb 103

Tendons 103

Tendon Repair 104

Extensor Tendons 106

Flexor Tendons 106

Ligaments and Suspensory Apparatus 106

Check Ligament 106

Suspensory Ligament 106

Blood Supply to the Lower Leg 107

The Hoof 107

The Hoof as a Plastic Structure 107

Effect of Movement on Hoof Structure 111

Functions of the Hoof 112

Shock Absorption 112

Grip 112

Circulation 113

The External Hoof 113

Wall 113

Sole 116

Frog 116

Hoof Horn 118

Internal Structures 118

Digital or Plantar Cushion 118

Lateral (Ungual) Cartilages 119

Pedal and Navicular Bones 119

The Balanced Foot 119

Assessment of Foot Balance 119

Static Foot Balance 119

Dynamic Foot Balance 120

Adaptations of Hoof Tissue 121

Summary Points 121

Q + A 122

5 The Digestive System 123

Foregut 124

Mouth 124

Oesophagus 127

Stomach 127

Gastric Juice 128

Small Intestine 130

Pancreas 132

Endocrine Functions of the Pancreas 132

Exocrine Functions of the Pancreas 133

Liver 134

Functions of the Liver 135

Hindgut 137

Large Intestine 137

Caecum 137

Large Colon 137

Small Colon 140

Rectum 140

Digestion in the Large Intestine 140

Equine Microbiota 140

The Gut and the Immune System 142

Summary Points 142

Q + A 143

6 The Respiratory System 145

Anatomy 146

Within the Head and Neck 146

Within the Chest 148

Blood Supply 149

Pleurae 149

Diaphragm 150

Physiology of Respiration 150

Pulmonary Ventilation 150

Pressure Changes during Breathing 151

Airway Resistance 151

Lung Air Volumes and Capacities 151

Dead Space 153

Regulation of Breathing 153

Respiratory–Locomotor Coupling 154

External Respiration or Pulmonary Gas Exchange 155

Internal Respiration or Systemic Gas Exchange 156

Transport of Oxygen and Carbon Dioxide Around the Body 157

Oxygen Transport 157

Carbon Dioxide Transport 157

The Oxygen Dissociation Curve 158

The Bohr Effect 158

Cellular Respiration 159

Aerobic Cellular Respiration 159

Aerobic Respiration of Glucose 161

Glycolysis 161

Link Reaction 161

Krebs Cycle 163

Electron Transport Chain 163

Aerobic Respiration of Other Fuels 166

Glycogen 166

LipidMetabolism 166

Protein Metabolism 167

Anaerobic Respiration 167

Summary Points 167

Q + A 168

7 The Circulatory System 169

Foetal Circulation 170

The Heart 171

Cardiac Output 172

Anatomy of the Heart 173

The Cardiac Cycle 175

Regulation of the Heart Beat 175

The Heart and Fittening/Training Horses 176

The Heart and VO2 Max 178

Heart Murmurs 178

Heart or Cardiac Arrhythmia 178

Second-Degree AV Block 179

Atrial Fibrillation (AF) 179

Sudden Cardiac Death 179

Blood Vessels 179

Arteries 179

Veins 180

Capillaries 182

Heart Evaluation and Examination 182

Electrocardiogram 182

Exercise Testing of Horses 183

Blood 184

Plasma 184

Red Blood Cells (Erythrocytes) 185

White Blood Cells (Leucocytes) 186

Granulocytes 188

Agranulocytes 189

Platelets (Thrombocytes) 190

Haemostasis or Blood Clotting 190

Blood Tests 191

Blood Typing 191

The Lymphatic or Lymph System 192

The Spleen 193

Summary Points 194

Q + A 194

8 The Nervous System 197

Nerves and Neurons 198

Neuroglia or Glial Cells 200

Organisation of the Nervous System 202

CNS 202

PNS 203

Action Potential 203

Resting Membrane Potential 204

Synapses 206

Transmission at the Synapse 207

Neurotransmitters 208

Endorphins and Enkephalins 208

Neuromuscular Junctions 209

The Brain 209

Forebrain 210

Hypothalamus 210

Thalamus 210

Cerebrum 210

Midbrain 210

Hindbrain 210

Spinal Cord 212

Reflex Actions or Arcs 212

Summary Points 212

Q + A 213

9 The Endocrine System 215

Hypothalamus 216

Pituitary Gland (Hypophysis) 217

Anterior Pituitary – Adenophysis 217

Pars Intermedia 218

Posterior Pituitary (Neurophysis) 218

Thyroid Gland 219

Thyroid Hormones 219

Parathyroid Glands 219

Adrenal Glands 220

Adrenal Cortex 221

Mineralocorticoids 221

Glucocorticoids 222

Adrenal Medulla 222

Pancreas 222

Secretion of Glucagon and Insulin 224

Thymus 225

Ovaries 225

Equine Chorionic Gonadotropin 226

Testes 226

Pineal Gland 227

The Neuroendocrine System 228

Circadian Rhythms in Horses 230

Sleep Patterns in Horses 231

Summary Points 232

Q + A 233

10 The Skin 235

Structure of the Skin 235

Epidermis 237

Stratum Basale 238

Stratum Spinosum 238

Stratum Granulosum 238

Stratum Lucidum 238

Stratum Corneum 238

Dermis 238

Sensation 239

Melanin 239

Sudoriferous Glands (Sweat Glands) 239

Sebaceous Glands 239

Hair 239

Hair Follicles 240

The Coat 241

Thermoregulation 241

Heat Conservation 243

Heat Loss 243

Sweating 245

Breaking Out 246

Dry Coat or Anhydrosis 246

Skin and Coat Colour 246

Summary Points 247

Q + A 247

11 The Senses 249

Transduction 249

Adaptation 249

Somatic Receptors 250

Thermal Sensations 250

Pain Sensations 251

Tactile Sensations 251

Itch Sensation 252

Proprioceptor Sensation 252

Special Senses 253

Sight 253

Visual Streak of the Eye 253

Colour Vision 254

Night Vision 254

Anatomy of the Eye 254

Chambers of the Eye 255

Photoreceptors 256

Transmission of Nerve Impulses to the Brain 258

Accommodation (Focusing) 258

Adaptation of the Horse’s Eyes to Light 258

Eyelids 259

Conjunctiva 259

Lacrimal Apparatus 260

Hearing and Balance 260

Anatomy of the Ear 261

Taste and Smell 264

The Olfactory System 265

Jacobson’s Organ 265

Summary Points 266

Q + A 266

12 Reproduction 267

Reproductive Anatomy of the Mare 267

Vulva 267

Vagina 269

Cervix 269

Uterus 269

Utero-tubular Junction 270

Fallopian Tubes 270

Ovaries 271

The Oestrus Cycle 272

Follicular Development or Oogenesis 275

Ovarian Changes during the Oestrus Cycle 275

Behavioural Signs of Oestrus in the Mare 276

Summary of Mare Behaviour through the Cycle 276

Endocrine Changes during the Oestrus Cycle 277

Artificial Control of the Oestrus Cycle 278

Light 279

Hormonal Methods 280

Postponing Ovulation 280

Reproductive Anatomy of the Stallion 280

Scrotum 280

Testes (Testicles) 281

Epididymis 282

Vas Deferens 284

Accessory Sex Glands 284

Vesicular Gland (Seminal Vesicles) 284

Prostate Gland 284

Bulbo-Urethral Gland (Cowper’s Gland) 284

Penis 284

Spermatogenesis 285

Acrosome Reaction 286

Endocrine Pathways in the Male 287

Fertilisation 287

Pregnancy Diagnosis 287

Foetal Sexing 288

Twins 289

Endocrine Maintenance of Gestation 289

Equine Chorionic Gonadotropin 290

Progesterone 290

Oestrogens 290

Relaxin 290

Gestation 291

Implantation and Placentation 291

Embryology 292

Phases of Equine Embryo Development and Migration 293

Phase 1 294

Phase 2 294

Phase 3 294

Phase 4 294

Phase 5 294

Phase 6 294

Timeline of Embryonic Development 294

The Foetal Endocrine System 295

Preparation for Parturition (Birth) 295

The Three Stages of Parturition 296

Stage 1 296

Stage 2 296

Stage 3 296

Induction 296

Lactation 297

Lactogenesis 297

Lactation Curve 298

Applied Reproductive Technologies 298

Artificial Insemination 298

Advantages 299

Disadvantages 299

Collection of Semen 299

Semen Preservation 300

Embryo Transfer 301

Advantages 302

Disadvantages 302

Donor and Recipient Mares 302

The Synchronisation Process 302

Collection of the Embryo 302

Transfer of the Embryo 303

Gamete Intrafallopian Transfer 303

Oocyte Transfer 303

Intracytoplasmic Sperm Injection (ICSI) 303

Summary Points 303

Q + A 304

13 Genetics 305

The Genetic Code or Genome 305

Chromosomes 305

Gene Expression 306

Mitochondrial DNA 307

The Y Chromosome 308

Alleles 308

Dominance 308

Sex Cells 309

Hybrids 309

Heredity 309

Sex Determination 310

Genotype and Phenotype 311

Polygenic or Multiple Gene Traits 311

Multiple Alleles 311

Sex Linkage 311

Lethal Genes 311

Lethal White Foal Syndrome (LWFS) 311

Foal Immunodeficiency Syndrome (FIS) 311

Lavender Foal Syndrome (LFS) 312

Severe Combined Immunodeficiency (SCID) 312

Congenital Curly Coat Syndrome 312

Epigenetics 312

Muscle Disorders 314

Nuclear Transfer (Cloning) 314

Parental Similarity of Clones 314

Mutation 315

Gene Mutation 315

Chromosome Mutation 316

Non-Disjunction 316

Polyploidy 316

Single Nucleotide Polymorphisms 317

The Myostatin Gene and Performance 317

Coat Colour and Genetics 317

Bay/Black 318

White (Albino) (WWorWw) 318

Grey (GG or Gg) 318

Roan 320

Spotting Patterns 320

Sabino (SB1) 320

Tobiano (TO or to) 320

Overo (O) 320

Appaloosa (LP) 320

Cream (C or Ccr) 321

Silver (Z) 323

Champagne 323

Pearl 323

Dun (D or d) 323

White Markings 323

Melanomas in Grey Horses 323

Exercise-Induced Pulmonary Haemorrhage (EIPH) or Epistaxis 323

Summary Points 324

Q + A 324

14 The Urinary System 325

Kidneys 325

Nephrons 327

Role of Tubules in Formation of Urine and in Homeostasis 331

Proximal Convoluted Tubule 331

Loop of Henle 332

Distal Convoluted Tubule 333

Regulation ofWater 334

Regulation of Permeability of the Collecting Ducts by ADH 334

Aldosterone 335

Acid–Base Balance 335

Extracellular and Intracellular Chemical Buffers 336

Protein Buffer System 336

Carbonic Acid–Bicarbonate Buffer System 336

Phosphate Buffer System 336

Carbon Dioxide Exhalation 337

Excretion of Hydrogen Ions 337

Acid–Base Imbalances 337

Micturition or Urination 337

Summary Points 338

Q + A 338

15 The Immune System 339

Health Versus Disease 339

Microbes 339

Disease Transmission Routes 340

Infection 340

Biofilms 341

Symptoms of Disease 341

Diagnosis 342

Pathogenic Organisms 342

Bacteria (Prokaryotes) 342

Invasive Properties 343

Spread of Bacteria 344

Mycoplasma Species 345

Antibiotics and Resistance 345

Viruses 346

Structure 347

Replication 348

Eukaryotic Pathogens 348

Fungi 348

Protozoa 350

Internal Parasites 351

Protection from Disease 351

External Barriers 351

Innate Immunity 353

Inflammation 353

Interferons 355

Complement System 356

Natural Killer Cells 356

Adaptive/Acquired Immunity 357

Types of Adaptive/Acquired Immunity 357

Antigens and Antibodies 361

Antigen Presentation 362

Ingestion of an Antigen – Mode of Action 362

T Cells and Cell-Mediated Immunity 363

Helper T Cell Activation 363

Cytotoxic T Cells 363

Summary Points 364

Q + A 364

16 Exercise Physiology, Functional Anatomy and Conformation 365

Exercise Physiology 365

Fitness 365

Horses at Rest 365

Exercise 365

Exercise and Energy 366

Fuels Available for Exercise 367

Immediate Response of the Horse’s Body to Exercise 368

Changes Occurring during Exercise 368

Homeostatic Mechanisms Involved during Exercise 369

LactateThreshold 370

Over-training 370

Recovery 370

Long-Term Responses of the Horse’s Body to Exercise 371

Fitness Training 373

PreliminaryWork 373

DevelopmentWork 374

FastWork 374

Interval Training 374

Aims of Interval Training 374

Monitoring Interval Training 375

Beginning Interval Training 375

How to Use Interval Training 375

Points Regarding Interval Training 375

Functional Anatomy 376

Centre of Gravity 376

Stay Apparatus 377

Moving the Front Legs 380

Moving the Hind Legs 380

Equine Biomechanics 381

Kinematics 381

Kinetics 381

Conformation 382

Ideal Conformation 382

Head 382

Topline 382

Neck 382

Withers 384

Chest 384

Shoulder 384

Elbow 384

Forelimb 385

Feet 386

Back 386

Hindquarters 387

Summary Points 390

Q + A 390

17 Teeth and Ageing 391

Equine Teeth 391

Wear and Tear 394

Ageing 396

Care of Equine Teeth 399

Summary Points 401

Q + A 401

18 Evolution, Classification and Behaviour of the Horse 403

Evolutionary Time Period 403

Classification 403

Species 404

Evolutionary Development 407

The Evolutionary Family Tree 409

Domestic Breeds and Types of Horses 412

Donkeys 412

Przewalski’s Horse 412

Mustangs 414

Behaviour of the Modern Horse 414

Innate Behaviour 414

Learned Behaviour 415

Habituation 415

Classical Conditioning 416

Operant Conditioning 416

Latent Learning 416

Insight Learning 416

Stereotypies 416

Imprinting 417

The Dopamine Receptor D4 417

Emotion 417

Summary Points 417

Q + A 418

A Anatomical Terms Based on theMedian Plane 419

B Haematology and Plasma Biochemistry Tests 421

C Functions, Sources and Deficiencies of Vitamins andMinerals in Horses 423

Index 429