Written By: Margaret Duxbury, DVM, University of Minnesota
Compulsive or 'stereotypic' behaviors are repetitive behaviors that serve no apparent function and occupy a significant portion of an animal's time. Common examples include crib biting and weaving. These problems are frustrating for horse owners. As a result, they have often been categorized as 'vices', a label that implies some fault or failing on the part of the horse. In reality, compulsive behaviors usually begin when there is something 'wrong' with the horse's environment.
Compulsive behaviors are not seen in feral, free ranging horses. In natural settings, horses graze 16-19 hours per day consuming a wide variety of plants. They chew greater than 30,000 bites per day, walking a few steps after every bite or two. They live together in relatively stable social groups exchanging an enormous amount of social information via subtle non-verbal mechanisms including touch, smell and visual changes in body posture and facial expression.
The horse's ability to cover long distances per day and to respond to refined social signals suits them well to our domestic needs. But it's a 'package deal'. The very same genes that enable horses to thrive on training and competition will tell them to move a certain amount per day, to forage and chew, and to form social bonds with other equines. Highly managed environments may not allow this. Some horses adapt to a restricted environment with out apparent problem. Others seem compelled to do what nature tells them—and this becomes the basis for the development of compulsive behaviors. A horse that repeatedly grabs a stationary object with its front teeth, pulls back and makes a grunting noise is said to be crib-biting.
Horses kept in stalls with limited access to other horses, and horses fed low forage diets are more likely to crib bite. Since satiety is tied to chewing in horses, cribbing may be an attempt to satisfy a severe case of 'the munchies' brought on by having too little to chew. Horses fed high concentrate diets are also at increased risk of cribbing. In one study, foals fed concentrates after weaning developed crib biting four times as often as those that were not. High concentrate diets increase gastric acidity and the risk of ulcers—which can increase the risk colic.
There are anecdotal reports that some horses with gastric ulcers may be more likely to crib or do things like eat dirt, however, this has not been proven in research. Equine saliva acts as a buffer to neutralize stomach acids. In horses, the sight or smell of food does not trigger salivation—but chewing does—and cribbing may too. Cribbing horses do not actually swallow air as previously believed. While owners are often concerned that one horse may learn to crib from watching another, this has not been documented, though cribbing may well arise in several horses under similar management.
A weaving horse repeatedly shifts its neck and its weight from side to side. Weaving is often triggered in situations where the horse would like to move or follow other horses but is prevented by a barrier. The incidence of weaving in stalled horses may be decreased when horses can see and touch other horses from multiple sides.
These behaviors serve no apparent function and occupy a significant portion of an animal's time. Treatment of compulsive behaviors can be difficult. Lack of environmental enrichment may encourage stereotypic behavior. However, ensuring a rich environment for a horse with an established problem may not be curative. What may start as a thwarted effort to accomplish a natural behavior may actually release tension for the horse. This release of tension reinforces the compulsive behavior making it more likely to occur again. The longer a compulsive behavior has been exhibited, the harder it is to treat. The behavior makes the horse feel good - and nothing we can do after the fact changes this. We can and do try, but prevention is our best tool. Devices such as anti-weaving bars and crib straps can physically prevent the horse from performing the stereotypic behavior, but do little to address the reason the horse began to weave or crib in the first place. Is it humane to simply bar the horse from behavior that may help it cope with an unsatisfactory environment? Environmental enrichment including increased foraging opportunities (offer a variety of hay types and ensure hay is available over night), adequate exercise and social interactions with other horses are important for both treatment of the problem and the welfare of the horse.
For more information on compulsive behaviors, please contact Dr. Duxbury at firstname.lastname@example.org.
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