CHAPTER 24 Management of Stereotypic Behavior (Stable Vices)
Horses may perform a variety of apparently functionless, repetitive behaviors, such as weaving, stall walking (stall walking), cribbing (also known as crib-biting or windsucking), and pawing. These types of behaviors have been referred to by many names, including stereotypic behaviors, stereotypies, stereotypes, obsessive compulsive disorders, compulsive disorders, vices, and habits. The motivation for these behaviors has historically been ascribed to general emotional states like boredom, frustration, or poor temperament, but it is now clear that specific causal factors exist for specific stereotypic activities in the horse.
Behavior problems are an unfamiliar field of practice for many veterinarians, so individuals outside the profession are often consulted for advice on such matters. However, many of these behaviors involve medical conditions, and many traditional treatments conducted by veterinarians may actually be to the horse’s detriment, so an understanding of the fundamental concepts underlying these problems and appropriate application of clinical skills is essential.
Some of these behaviors are technically considered to be an unsoundness and can reduce the value of the horse because it is often thought that the behaviors can cause ill-thrift or more specific health problems; for example, it is often reported in the popular literature that weaving makes a horse more likely to suffer from tendon problems, or horses that crib can swallow so much air that they are prone to colic. However, the scientific evidence in support of such assumptions is often absent, and the picture is much more complicated than is widely appreciated. The common lack of understanding of the nature of these problems results in many owners seeking to control them by whatever means they can, with varying success and varying levels of cruelty, possibly on the advice of a well-meaning but misguided veterinarian. Scientific research now suggests that punishment or physical prevention of stereotypic behaviors is generally detrimental to the horse’s well-being; punishment does not address the underlying motivation or causal factors, which can be a welfare concern in their own right, and is likely to increase frustration. In most instances, allowing expression of the behavior and educating the owner are preferable to simple prevention. Early intervention is warranted because there is growing evidence that, with time and in certain as yet unknown conditions, deep-seated neurologic and cognitive changes may develop with the result that the problems will no longer be responsive to environmental intervention.
Stereotypic behaviors are more common in Thoroughbreds and Warmbloods than in Standardbreds, and there is evidence of the problem being more common in certain familial lines. This does not mean that the behaviors are inherited, but rather that there is a heritable component to the problem. Other risk factors relate to the environment and include the diet and feeding regimen of the horse. Reduced and less frequent feeding of forage and the feeding of hay as opposed to other forages increase the risk of these problems. Social factors are also important, with reduced social contact, a dominant dam, and weaning (especially weaning by confining foals to a stall) further increasing the risk. Lack of time spent outdoors has been associated with increased risk, and the balance between exercise and diet may also be important. It seems that almost any factor that increases stress or stress perception has the potential to sensitize individuals to these problems; therefore, general stress management should form part of an overall husbandry review of individual cases. Despite some commonly held beliefs to the contrary, there is no evidence of an association between coat color and these behaviors in the horse.
In summary, genetic as well as environmental factors, especially around the stressful time of weaning, appear to have important nonspecific effects on the risk of an individual horse developing some form of repetitive behavior. These factors probably alter the risk of stress-induced sensitization of the relevant pathways, but specific factors are known to predispose horses to developing problem behaviors. Contrary to popular belief, there is no evidence that these behaviors will be copied by a horse that is not otherwise predisposed to the problem. Therefore, management of risk factors remains the mainstay for intervention in horses with these problems.
Weaving is an obvious lateral swaying movement of the head, neck, forequarters, and sometimes the hindquarters, whereas stall walking refers to repetitive tracing of a circular route within the stall; both conditions are believed to develop in slightly more than 2% of stabled domestic horses in developed countries, but there is considerable variation in frequency among populations. The two behaviors are probably both expressions of frustrated locomotor behavior in different circumstances and are more common in horses in which exercise is restricted, especially those that are expected to be very active at other times, such as endurance horses (in which there may be a mismatch between diet and exercise) or those turned out into smaller paddocks (Box 24-1). The behavior is typically manifested at times of highly anticipated arousal or acute frustration, such as just before feeding or turnout, and so is not associated with “boredom.” Both problems have a median age of onset of just over 1 year. Despite these similarities, there are differences between these conditions, and it has been suggested that stall walking is more common and weaving less common among Arabians. In Canada, it appears that weaving is uncommon among Standardbreds and ponies, and stall walking is less common among Quarter Horses, Warmbloods, and ponies.
Although it is often said that weaving affects performance, I am aware of no data to support this contention. Some have also suggested that the behavior puts extra strain on the tendons, but because horses naturally walk around all day and the footfalls of the weaving horse are usually in the walk sequence, this seems unlikely. Given the functional anatomy of the circulatory system of the distal portion of the limb, it might be that, compared with standing idly in a stall, some activity may actually improve circulation to these structures and so reduce the risk of injury. Horses with pain in all four feet may appear to shuffle in place, so it is important to rule out lameness in a horse being examined for apparent weaving behavior.