DR MARK HILLYER/NEH
Pawing the ground is a common sign of colic symptoms, as are lack of appetite, lying down and rolling; horses will sometimes sit like a dog to relieve discomfort
all types of colic and were drawn from a study of over half of all the thoroughbreds in training in the UK at the time. Whilst differences will invariably exist between different individual premises, this study allows a baseline estimate for the overall prevalence of colic in the thoroughbred in training. Other studies show a broadly similar estimate for the prevalence of colic in breeding thoroughbreds.
Risk factors for colic Further studies have specifically looked at factors which might predispose a horse to being at an increased risk of colic. Many of these studies have now been undertaken and, whilst some looked only at specific types of colic or specific groups of horses, it is now possible to have a more global understanding of what might be the important risk factors. Age seems to have little effect, except at the extremes where youngsters and older horses appear at increased risk. Breed also seems to have little effect other than for the Arabian, who appears at increased risk. There is also little effect of gender on the overall colic frequency. However, within specific types of colic, such as those associated with lesions caused by foaling, there will be an obvious gender effect as these types of colic are seen only in the broodmare. Almost all epidemiological studies of colic have identified a strong effect of a previous episode of colic resulting in an increased risk for a further episode of colic. This is consistent with the previous finding that some individual horses appear prone to colic and suffer multiple episodes, whilst others on the same premises and under the same management will show no colic signs. As well as the risk being increased by a horse having had a previous colic episode, the risk of future colic is further increased if a horse has had a THOROUGHBRED OWNER & BREEDER INC PACEMAKER
previous episode which required surgery. One other factor that has repeatedly been shown to be associated with an increased risk is the performance of windsucking/crib-biting behaviour. Currently it is not known if this association is cause or effect, but it is known that a ‘cribber’ will be at increased risk of suffering colic episodes compared to a horse who does not exhibit this behaviour. The risk factors already mentioned are classified as unalterable. The owner of an aged Arabian horse with a history of previous colic episodes that required surgical treatment and who is also an habitual crib-biter can only accept that this horse will be at significantly increased risk of further colic. However, in most instances these further episodes of colic will be benign and/or medically treatable. Fortunately there are also a number of alterable risk factors which have been identified. By definition, knowledge of these, and their avoidance, has the potential to allow an owner to reduce the risk of their horse suffering from colic. In general, both increased duration and increased intensity of exercise, and more importantly a sudden change in exercise level, are associated with an increased risk of colic. This is particularly seen for one specific type of colic, the impaction of the pelvic flexure of the large colon. This is commonly seen associated with a recent reduction in level of exercise such as when a horse in full training has to change to enforced box rest as a result of an orthopaedic injury. This is further borne out by studies showing increased colic risk is associated with an increasing proportion of the day spent stabled and a decreased proportion of the day spent at pasture. Multiple studies have looked at the effects of feeding on the incidence of colic. Unfortunately, specific results can be hard to
interpret as not only do feeding regimes differ markedly between premises but in many instances the feeding regime will vary between horses in adjacent stables on the same premises. In summary, an increased risk of colic is associated with increased feeding of grain and concentrates and offering fewer but larger feeds. There are a few specific colic causes which result from particular feeding practices. Use of Coastal Bermuda hay (particularly in North America) is associated with an increased risk of creating an impaction in a specific region of the small intestine. Horses kept in sandy paddocks with short or sparse vegetation are prone to inadvertent sand ingestion which accumulates in the large intestine and can cause recurrent colic and impactions. Intestinal parasites continue to play a major role in some types of colic. The large red worms, the small red worms, tapeworms and ascarids can each be responsible for specific types of colic. Control or elimination of these parasites will therefore reduce the risk and incidence of these types of colic.
Prevention Unfortunately, as already mentioned, the design and function of a horse’s gastrointestinal tract is such that elimination of all colic episodes is unlikely to be an achievable aim. However, knowledge of the expected rate of colic episodes does allow us to recognise a situation where a group of horses appear to be suffering an abnormally high incidence of colic. In this situation, further investigation of possible risk factors is warranted, with particular emphasis on identifying any alterable risk factors. If these are found there is then the potential to alter the management in order to reduce or remove these risk factors and hopefully reduce the colic incidence.
Conclusion Whilst there is no doubt recent studies have significantly advanced our understanding of the causes of colic, it is sobering to review the conclusions reached from careful observation over 100 years ago by our forebears. Caulton Reeks, in his treatise of the common colics of the horse published in 1909, stated: “Far and away the most common cause of equine colics is the one that may be best described by the single word ‘domestication’.” This is probably just as true today as then. Dr Mark Hillyer is the Head of Soft Tissue Surgery, Internal Medicine and Intensive Care at Newmarket Equine Hospital
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