Cribbing is one of the most common vices horses can have. Also known as crib-biting, it is frequent, repetitive action that animals engage in with no apparent function.
When a horse cribs, it grasps a flat surface with its front incisor teeth, arches its neck and gulps air, creating a grunt.
The cause is unknown, but the lack of cribbing in wild horses supports that it is a learned behaviour of domesticated horses, rather than a behaviour that is innate to the species.
Some horses are more prone to developing this habit than others. Long hours in stalls and limited social contact with other horses is a major risk factor. Others include sudden versus gradual weaning and diets that are high in carbohydrates, such as grains and low in forage. There is also an association with horses that travel for performance activities such as racing and showing.
Certain breeds, particularly Thoroughbreds and Warmbloods are at higher risk, and mares are less likely to crib compared to stallions and geldings.
The exact function of cribbing behaviour is unknown. Horses that crib may be doing so to cope with stress, which is supported by evidence of reduced heart rate, and in some studies, decreased stress hormone (cortisol) in the blood after they crib.
Another theory is that cribbers may also have gastrointestinal upset from their high concentrate diets. The behaviour may alleviate this through increased saliva production, which reduces acid in the stomach and intestines.
Although the function of cribbing remains a mystery, it has negative consequences. It can be distressing to witness for owners and handlers. It can decrease the value of an animal for resale as many people view it as an undesirable behaviour.
Since the horses grasp surfaces with their teeth to crib, those that perform this behaviour prematurely wear down their incisor teeth. Finally, there is some evidence that cribbers are prone to developing serious medical conditions such as colic.
Treatment of cribbing should be attempted as soon as possible when the behaviour is identified since some studies have found that it can be reversed.
Horses that crib should be assessed by a veterinarian for any underlying medical condition that may be contributing, such as stomach ulcers. Management interventions could stop the behaviour from becoming an ingrained habit. Owners can remove all surfaces from stalls and enclosures that horses could crib on to reduce their ability to crib.
While there are commercial cribbing collars that prevent horses from arching their necks, these may have significant negative impacts on welfare. Collars prevent the behaviour but do nothing to alleviate the underlying causes and stress.
Horses can be fed high-fibre diets from devices that slow down eating, such as slow feed hay nets and hay balls. This will increase the time it takes to eat, producing ample saliva and increasing their activity.
A 2016 Italian study found that a feed dispenser decreased the amount of time horses spent cribbing and increased how long it took to consume their food. But the feeder did not completely eliminate cribbing behaviour.
There may be some benefit to exploring the use of concentrate feeders to prevent or reduce the behaviour. Horses should have the maximum possible amounts of turnout/grazing time and be kept in groups for adequate social contact.
Another preventive measure is to use gradual instead of abrupt weaning practices and keep weanlings on pasture.
There is little scientific evidence that horses learn to crib from others. For instance, a new horse may be introduced to a barn and be stabled near a habitual cribber. If the new horse starts cribbing, it is challenging to tease out if they learned from observing the other horse or if it is responding to the same management factors.
Many factors about cribbing remain unknown, including the underlying causes and reasons why horses start the behaviour. Once started, early intervention is the best hope to eliminate this undesirable behaviour.