Cribbing (horse)

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. ==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. 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 ==Health effects==

There is evidence that stomach ulcers may lead to a horse becoming a cribber, 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. There is evidence that stomach ulcers may be correlated to a horse becoming a cribber. The most popular cases of crib-biting come from racetracks, and it is believed to have derived from husbandry systems at the racetracks. It was also found that the descendants of a crib-biter were more likely to perform the behaviour due to a genetic component. Gastrointestinal environment and feeding routines were also a crucial topic, hinting that perhaps grain concentrations, grain ratios and forages were the main cause of ulcers, causing the animal to perform the oral stereotypy as a method of comfort. A study in 2009 found that 48.8% of US horse owners believed that cribbing could be learned by observation, but research demonstrated that only 1.0% of horses developed cribbing after being housed in sight of an affected horse. ==Functions==

Stereotypies are sometimes considered to be a coping mechanism for animals experiencing stress. A physiological stress response can be induced by injecting an animal with ACTH and the animal's ability to cope with this stress can be monitored by measuring salivary cortisol. In a 2015 study, after ACTH injection, cribbers had higher cortisol levels than non-cribbers. Furthermore, cribbers which did not perform the stereotypy during the 3-hrs of testing had higher cortisol levels than non-cribbers, whereas those performing the stereotypy did not. The researchers concluded that cribbing is a coping mechanism to stressful situations and that because of this, it should not be prevented. Cribbing and wind-sucking may cause a sensation of pleasure by releasing endorphins in the horse's brain. therefore, if cribbing and wind-sucking have one of the above possible functions, it may be inappropriate to label them as a stereotypy. However, as the causes and resulting reinforcement for these behaviors are probably multifactorial and they remain abnormal behaviors, this indicates that husbandry changes are needed for animals that exhibit cribbing or wind-sucking. A study suggested was that ghrelin levels were higher in a crib-biting horse than in those who did not perform the behaviour. Meaning that cribbing did not provide comfort for ulcers, rather that it stimulated/caused this issue. ==Treatment==

Several methods have been devised to prevent cribbing once the behavior has started. However, some ethologists have argued that prevention of the behavior without addressing the causes is not a cure and may result in cribbing being expressed in a modified form, or may interfere with an animal's attempt to adapt to its environment. Dietary and management It has been shown that feeding cribbing horses an antacid diet can significantly reduce the frequency of the behavior. A growing body of work suggests that fat and fiber-based diets may also result in calmer patterns of behavior. Physical devices There are a number of traditional devices used to minimize or prevent cribbing and wind-sucking. However, the effectiveness of these methods is arguable since they do not address the underlying causal factors. If the behaviour is stress related, the use of a cribbing collar may be counterproductive because it would not allow the animal to release the stress hormones by performing the behaviour and that cribbing may be beneficial in reducing stress. Covering exposed edges with metal or wire or painting surfaces with bitter substances such as carbolineum or a commercial "chew stop" product may reduce chewing-related damage to surfaces, though this does not prevent edges from being gripped by the teeth. Surgical and others Other methods to prevent cribbing have included surgery, acupuncture, use of pharmaceuticals, operant feeding, and environmental enrichment. However, a study found that the use of pharmaceuticals was expensive, less popular and less effective. One surgical technique is the modified Forssell's procedure in which muscles and nerves in the ventral neck region are cut as well as some muscle tissue being removed. This makes it more difficult for a horse to contract the larynx and exhibit cribbing. An adaptation of this technique using a laser has proved successful in preventing some cribbers from exhibiting the behavior, although this was less successful in horses which had been cribbers for more than three years prior to the surgery. It has been found that this method was successful in 84.4% of cases. For those that the surgery was not found to be effective, relapse time occurred within six months to two years after the surgery had taken place. ==References==