Cribbing (horse)

Cribbers may cause serious damage to wooden fences and stalls

Cribbing or crib biting is an abnormal, compulsive behavior or stereotypy seen in some horses, and considered a stable vice. It involves the horse grabbing a solid object such as the stall door or fence rail with its incisors, then arching its neck, pulling against the object, and sucking in air.^[1] Windsucking is a related behavior whereby the horse arches its neck and sucks air into the windpipe without needing to grab a solid object. Windsucking is thought to form part of the mechanism of cribbing, rather than being defined as an entirely separate behavior.^[1] Cribbing and windsucking have been linked as a causal effect to colic and stomach ulcers.^[2]

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.^[3]

Negative consequences

Cribbing and windsucking have been linked to a higher incidence of stomach ulcers and are also defined as risk factors for certain types of colic.^[2] Colic can also be a consequence of wood chewing due to the ingestion of wood splinters.^[4] Both cribbing and wood chewing can cause excessive wearing and deterioration of the teeth in severe cases.^[5] Horses displaying these behaviors may be less desirable to potential buyers and may be devalued as a consequence.

It has been anecdotally reported that horses can learn to copy these behaviors from other horses, although this has not been substantiated by scientific study.^[6] Wood chewing also is destructive to barns and fences, sometimes requiring costly repairs and ongoing maintenance.

Causes

Wood chewing has been linked with dietary deficiencies, and often can be remedied with a balanced diet or dietary supplementation.^[4] Some cases are thought to be linked to boredom or anxiety, often related to confinement. Boredom, stress, habit and addiction are also all possible causes of cribbing and windsucking.^[3] 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.^[7]

Researchers now generally agree that cribbing and windsucking occur most often in stabled horses, although once established in an individual horse, the horse may exhibit these behaviors in other places.^[3] Recent studies indicate cribbing occurs more frequently in horses that were stable-weaned as foals than in those that were pasture-weaned. In the same study, feeding concentrates after weaning was associated with a fourfold increase in the rate of development of cribbing.^[8]

Functions

Cribbing and wind-sucking may cause a sensation of pleasure by releasing endorphins in the horse's brain.^[1] More recently, it has been suggested that the increase in saliva produced during wind-sucking could be a mechanism for neutralizing stomach conditions in stable-kept, grain-fed horses.^[8] Stereotypies have been defined as "repetitive, invariant behaviour patterns with no obvious goal or function",^[9] 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.

Treatment

It has been shown that feeding cribbing horses an antacid diet can significantly reduce its frequency.^[7] Current research indicates that the prevention of cribbing and related behavior is based upon management conditions which allow daily free movement and feeding practices that provide higher amounts of roughage and limited amounts of concentrates.^[10] A growing body of work suggests that fat and fiber-based diets may also result in calmer patterns of behavior.^[6]

There are a number of traditional methods for minimizing or preventing cribbing, windsucking, and wood-chewing. However, the effectiveness of these methods is arguable since they do not address the underlying causal factors.^[11] One method involves the horse wearing a collar-like device that prevents it from arching and swelling its neck to suck in air. Covering exposed edges with metal or wire or painting surfaces with bitter substances such as carbolineum or a commercial "chew stop" product may reduce wood-chewing, though do not entirely prevent edges being gripped by the teeth. Other methods to prevent cribbing have included surgery, acupuncture, use of pharmaceuticals, operant feeding, and environmental enrichment.^[11]

References