VOLUME 22 • © HORSES For LIFE™ Magazine
C. J. Nicol
Division of Animal Health and Husbandry, Department of Clinical Veterinary Science, Langford House, Langford, North Somerset, United Kingdom.
Equine stereotypies such as weaving, Crib-biting and box - walking are frequently described as "stable vices" and veterinary interest has generally focussed on the deleterious effects that may be associated with their performance. Many owners and veterinarians have pursued strategies to prevent the performance of stereotypies that include the use of physically restrictive devices, electric shock, and surgery . These methods are, in many cases, ineffective , they may cause distress or harm to the horse, and they address symptoms rather than underlying causation. Pharmacological approaches to treatment have also been suggested. Dopamine pathways are intimately related to the appearance of stereotypic behaviour and opiate transmission regulates dopamine release, such that agonists and antagonists of enkephalin receptors can induce or suppress stereotypy . This has led to studies looking at the efficacy of opioid antagonists as "treatments" for equine stereotypy. One study found transient elimination of crib-biting in all subjects treated with naloxone, nalmefene or diprenorphine . Another study reported that weaving was reduced by administration of an opiate antagonist, although a serotonin transport inhibitor, and a neuroleptic were also effective . The difficulty with such findings is that these pharmaceutical agents have many additional effects e.g. naloxone is a cataleptic and an appetite suppressant, and may reduce the performance of other functional behavioural systems. The effects of such drugs on the horse’s perception of its environment and on its overall welfare are not known. Of crucial significance to all attempts to treat the symptoms rather than the causes of stereotypy is recent work that suggests that some deleterious "effects" of stereotypy (e.g. digestive disorders, colic) may in reality reflect underlying problems that the horse is attempting to ameliorate by the performance of the stereotypy. In such cases, attempts to prevent the behaviour could do more harm than good. This dilemma for the veterinarian emphasizes the need to understand more about the causes and functions of equine stereotypies.