Cribbing is a form of stereotypy (equine oral stereotypic behaviour), otherwise known as wind sucking or crib-biting. Cribbing is considered to be an abnormal, compulsive behavior seen in some horses, and is often labelled a stable vice. The major factors that cause cribbing include stress, stable management, genetic and gastrointestinal irritability.
Cribbing was mentioned in the literature as early as 1578 and occurs in 2.4-8.3% of horses depending on breed and management.
A similar but unrelated behavior, wood-chewing or lignophagia, is another undesirable habit observed in horses, but it does not involve sucking in air; the horse simply gnaws on wood rails or boards as if they were food.
Description
Cribbing, or crib biting, involves a horse grasping a solid object such as the stall door or fence rail with its incisor teeth, arching its neck, and contracting the lower neck muscles to retract the larynx caudally. This movement is coincided with an in-rush of air through the crico-pharynx into the oesophagus producing the characteristic cribbing sound or grunt. Usually, air is not swallowed but returns to the pharynx. It is considered to be an abnormal, compulsive behavior or stereotypy, and often labelled as a stable vice.
Wind-sucking is a related behavior whereby the horse arches its neck and sucks air into the windpipe but does so without grasping an object. Wind-sucking is thought to form part of the mechanism of cribbing, rather than being defined as an entirely separate behavior.
Wood-chewing
A similar, but unrelated behavior, wood-chewing (lignophagia), is another undesirable behavior sometimes observed in horses. The horse gnaws on wood rails or boards as if they were food, but it does not involve sucking in air.
Prevalence and incidence
It is reported that 2.4–8.3% of horses in Europe and Canada are cribbers and that cribbing can occupy 15-65% of an individual horse's daily time budget. A postal survey in 2009 found that an average of 4.4% horses in the US are cribbers, but 13.3% of Thoroughbreds perform the behavior. Young Thoroughbred and part-Thoroughbred horses fed concentrated food after weaning are four times more likely to become cribbers than foals not fed concentrate. In several studies, Thoroughbreds consistently have the greatest prevalence of cribbing compared to other breeds. It was found that 11.03% of racehorses performed one or more abnormal stereotypical behaviour that lead back to animal welfare and husbandry systems.
Wind-sucking occurs in 3.8% of non-racing horses in the US. One study shows that stereotypes in general, including cribbing, are more prevalent in dressage horses compared to several other uses.
Geldings and stallions are more likely to exhibit cribbing than mares and the behavior has been reported as occurring in horses on pasture.
Health effects
There is evidence that stomach ulcers may lead to a horse becoming a cribber, and that cribbing may be a coping mechanism in response to stress.
A 1998 study found that cribbing increased endorphins and found no evidence that cribbing generally impairs the health of affected horses, but later studies reported that cribbing and wind-sucking were related to a history of colic or the subsequent development of colic. A study found that horses would perform the cribbing behaviour in attempt to decrease the cortisol levels that can be brought on by stressful situations. According to this study, the long-term release of stress hormones can be harmful and can cause cardiovascular diseases, depression and immunosuppression.
Causes
Boredom, stress, habit, and addiction are all possible causes of cribbing and wind-sucking. It was proposed in a 2002 study that the link between intestinal conditions such as gastric inflammation or colic and abnormal oral behavior was attributable to environmental factors. There is evidence that stomach ulcers may be correlated to a horse becoming a cribber.
Stress is induced when environmental demands produce a physiological response, if that response has a long duration period, it exceeds the normal, natural regulatory ability of the organism. Stress has been found to be a major contributing factor to horses developing this oral stereotypic behaviour. A study suggested that the animal uses cribbing as a coping method when it cannot escape a fearful or stressful situation, or when it has been socially isolated or confined.