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- Herausgeber: Crowood
- Kategorie: Fachliteratur
- Sprache: Englisch
- Veröffentlichungsjahr: 2013
Understanding the Horse's Feet sets out to explain the complexity of this subject in terms that the lay person can understand, and help the horse owner to have confidence in discussing foot-related issues with their vet or farrier/trimmer. The perennial problem of laminitis is examined in depth, together with other conditions that commonly affect the horse's foot. Topics covered include: The structure of the horse's foot; Examining horses' feet; The function of the hoof and the other foot structures; Laminitis; Investigating lameness. A practical guide to understanding the complexities of the horse's feet, aimed at horse owners, riding instructors, veterinary nurses and students. Superbly illustrated with 228 colour photographs and diagrams. John Stewart is an experienced vet and has his own equine practice.
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Copyright
First published in 2013 by The Crowood Press Ltd Ramsbury, Marlborough Wiltshire SN8 2HR
www.crowood.com
This e-book first published in 2013
© John Stewart 2013
All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publishers.
British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library.
ISBN 978 1 84797 557 7
Diagrams by Charlotte Kelly
Dedication Dedicated to Caillou, and to all the horses, ponies and donkeys that have not survived laminitis
Contents
Introduction
After I had agreed to write this book, it did not take me long to realize the enormity of the task I had set myself. I thought about the thousands of articles and hundreds of books already written about horses’ feet and wondered what I could possibly contribute to the topic. I had read enough of these papers and spoken to sufficient vets, farriers and trimmers to know that there was, and still is, significant disagreement on many aspects of the horse’s foot and its function – so not only was I to write on a subject where there are so many different opinions, I also had to do it in a way that would be understandable to horse owners. Yes, I panicked.
In the past, the majority of owners relied on their farrier or vet to advise them on hoof care, but nowadays, particularly with the advent of the internet, owners are doing their own research and many are becoming more proactive in the foot care of their horses. The problem for an owner is to know how much of the information available is fact, or how much might be just conjecture, and this probably applies as much to what is found in ‘traditional’ text books as the more speculative suggestions that circulate on some websites and internet forums. It does seem that some things have been repeated so often that they have been accepted as fact, and I find I am not the only person to question the veracity of some of these ‘facts’.
Part of the fascination about horses’ feet, and the problems they develop, is that there is very little that can be considered ‘black’ or ‘white’, and there are endless shades of grey, depending on the horse, its environment, its diet or its type of work – however, this is a great part of the frustration, too. This is because something that is right for one horse might be unsuitable or impractical for another, and something that is suitable for a horse at one time may then become the wrong thing to do for it in different circumstances. Nowhere does this become more pertinent than when dealing with laminitis (seeChapter 7), but it applies to other situations and conditions too. Although my aim has been to provide sufficient information about the grey areas for an owner to be able, with the assistance of their hoof-care professional, to make the right decision at the right time, the book’s content has been influenced by the fact that many farriers and trimmers (and vets, too) are set in their ways and tend not to be open-minded to new or different ideas. Too often I have been made aware of an owner’s concerns being brushed aside, so I have felt it necessary to go into greater depth than many other ‘books for owners’ in the hope that a greater understanding of problems will carry more weight with these ‘professionals’. I know that for many readers, parts of the book (Chapter 2, in particular) will be a challenge because they will encounter a vocabulary that is unfamiliar to them, but I believe some knowledge of the anatomy and function of the structures of the foot will help them understand the chapters that follow. If the reader is stimulated to find out more about the horse’s foot, which is what I hope to achieve, understanding these terms will also help – and may even be necessary – when reading other books and articles. The areas where there is in-depth information generally cover problems or situations that an owner is more likely to be confronted with, but also topics where I have introduced some novel concepts that need an explanation. Other areas where I have provided less information may be equally important, but I have felt they were either rare conditions or ones that would necessitate direct veterinary involvement.
I may well receive criticism from some people for including some of my own theories which are the results of my research but have not been ‘verified’. In the final chapter I describe the routes that my studies have taken, and the reasons for the conclusions I have come to, but because a large part of these investigations have been carried out without any fancy equipment and have mostly been from close examination of the horse’s foot, I am confident that other people will find the same things, if they look.
For brevity’s sake I have often used ‘horse’ to refer to ‘horse, pony and donkey’, and ‘man’ to include men and women. However, when it comes to foot care, my use of ‘farrier’ to include ‘farrier, horse-shoer and foot trimmer’ is perhaps more controversial. It applies to when foot balance and trimming is being discussed, since this applies to all three – though when I talk about having shoes on the feet it obviously no longer includes the barefoot trimmer. Although this book is about feet, it is vitally important not to consider them in isolation because the feet affect the rest of the horse, and the rest of the horse affects what happens to the feet. I have to confess that, whether it is a live horse, or a sculpture or a picture of one, the first things I look at are its feet; however, I do then always look at the ‘whole picture’ – at the beauty and the athleticism of this wonderful creature.
Fig. 1 Memorial to the Royal Scots Greys (1906), Princes Street, Edinburgh.
1 Evolution
If you place your hand on a table and, while leaving the finger tips in contact, raise it up until it is vertical, you will be left with just one fingernail touching the table. This illustrates the adaptive process in the horse’s foot which has taken place over millions of years, starting with the horse’s ancestors, Eohippus, up to the horses and ponies known collectively as Equus, which are around today.
Fig. 2 The bones of the digits of 1. Eohippus, 2. Mesohippus, 3. Merychippus, 4. Pliohippus, 5. Equus.
Ancestors of the horse existed fifty million years ago, but were very different to the creature that we recognize now. Eohippus was a small hare-like animal, living and running around in swampy undergrowth on feet with four long splayed toes. As the climate changed and became drier, the swamps and forests gradually disappeared and were replaced by open plains, and Eohippus had to adapt to take advantage of this new environment in order to survive. Modifications in its tooth structure enabled it to cope with grazing pasture rather than browsing bushes, and by changing its limb structure it was better able to survive in the open ground.
The limb changes included increasing the length of the legs, which allowed these prehistoric horses to take longer strides and so enabled them to run faster to escape from predators. Part of this leg-lengthening process was achieved by raising the digits to a more upright position. In the exercise described in the first paragraph, when you raised your hand from the table, the first finger to lose contact was your thumb; this digit was in fact already absent in the Eohippus, which had only four toes – but when you raised the hand further, the little finger lost contact, and this demonstrates the adaption that occurred over twenty million years, and can be seen in the Mesohippus, which had only three toes.
In the next twenty million years the digits became even more upright, with the inside and outside toes reducing in size so that they probably only made contact in wetter ground: the horse that characterized this evolutionary stage was called the Merychippus. The Pliohippus, which lived between ten and one million years ago, had one long toe, and Equus, the modern horse, adapted further to end up moving around on its middle finger nail, the hoof. The remnants of the other two digits were retained as the splint bones, lying just to the back of the cannon bone (the third metacarpus) and acting as support to the horse’s knee (the equivalent of our wrist).
The anatomy of the equine digit is somewhat different from our equivalent finger, although the basic form is similar. If, with a straight arm, you press down on your middle finger till your finger is bent back by about forty-five degrees to the perpendicular, this is the equivalent position of the horse’s lower limb.
ADAPTATIONS NECESSARY FOR EOHIPPUS’ SURVIVAL
So what were the adaptations required in Eohippus in order for him and his descendants to survive the change from forest to prairie? Already mentioned is the reduction in the number of digits, with more toes being of benefit in marshy ground, but a single one being better for firmer ground. However, in order to survive, these prehistoric horses also needed stamina to endure the long migrations required to find food and water, and the ability to remain standing a lot of the time in an energy-efficient way.
The Requirement for Speed
The speed of movement of an animal depends on the length and frequency of its stride: the longer and quicker the stride, the faster the animal will go. As well as lengthening the lower bones of the limbs and adopting a more upright posture, an increase in stride length in the horse was achieved by an evolutionary change which resulted in the loss of the clavicle (collar bone), thereby allowing a greater range of movement of the shoulder.
An increase in stride frequency was achieved as a result of a number of evolutionary changes, which included the reduction in weight of the lower limb by reducing the number of digits (as explained above). As the lower bones of the legs became longer, the upper bones of the limb remained short, and the heavy muscles that attach the trunk to these bones became more powerful. Reciprocal pulley systems evolved, with the arrangement of the tendons allowing the limb joints to bend or straighten together – wind resistance is reduced by the horse being able to fold the legs up under the body when he is moving at speed.
The Requirement for Stamina
The stamina required for long migrations was improved by evolving with ‘energy-efficient motion’. The tendons and ligament that support the fetlock joint – the ‘suspensory apparatus’ – evolved to be better able to store energy, to act like a spring, and as the leg bones became longer, so too did the tendons, to produce larger ‘springs’. This reduces the energy required by the muscles when the horse moves, allowing it to travel further with less effort.
The Requirement to Save Energy while Standing
As the horse evolved to be a plains-living animal, it increasingly relied on flight to escape from predators, and it was therefore important that it stayed on its feet to enable a quick getaway. It developed mechanisms to enable it to rest whilst standing: these are referred to as its ‘stay apparatus’. This describes the system of ligaments in the horse’s legs, which help to support it when it is standing, so that it can maintain the limb joints extended with minimal energy use. It can also ‘lock’ the patella (the knee-cap) in the hind legs, and has supporting ligaments to the superficial and deep digital flexor tendons – the superior and inferior ‘check’ ligaments – which allow the muscles to relax while tension is maintained in the tendons, thus conserving energy.
EQUUS
Along with our domesticated horses, ponies and donkeys, the species Equus includes the zebra, wild asses, and the only species of wild horse surviving, the Mongolian wild horse, or Przewalski’s horse, named after the Russian explorer who discovered it. These horses would be extinct in the wild were it not for breeding programmes in zoos which have allowed their reintroduction to Central Asia, and the re-establishment of a viable population.
Man has only been involved in the selective breeding of horses within the past three and a half thousand years, since they were first domesticated, thereby producing the diverse range of breeds that we see today. Initially, domesticated horses were used for work and war, but whereas the donkey is still used in many countries as a ‘beast of burden’, the role of the horse has changed, and in most countries it is now mainly used for pleasure, and often in the pursuit of sports.
Fig. 3 Two young Przewalski stallions – part of the conservation programme at Marwell Wildlife, Hampshire, UK (Photo courtesy of Martin Wilkie).
Selective breeding has produced stronger animals to cope with the ‘unnatural’ situation of carrying a rider, but by breeding for certain sporting requirements, some other, more detrimental, characteristics have been perpetuated. At the individual level, many are bred for sentimental reasons or financial gain, rather than concentrating on producing offspring of better structural quality. Unfortunately, man has also significantly altered the lifestyle for these domesticated horses, away from the environment in which they evolved to survive. Providing a diet that is often far removed from the foodstuffs and forage that would be available in the wild, and limiting the horse’s opportunity to satisfy its innate requirement for movement, has resulted in changed metabolic processes in its body, and in particular in its feet – which is the aspect of greater interest to us.
Fig. 4 The Finals – batik by Rosi Robinson.
