Equine Self Mutilation Syndrome (ESMS) is the name given to a pathologic condition that goes beyond simply biting at irritated or itchy tissue. Affected horses obsessively and repeatedly bite at specific areas on their body, eventually resulting in severe trauma to the area.

The most common target areas are the flank, stifle, chest and the fronts of the forelimbs. The horse may stare at the area, squeal, spin, bite at the air and then bite the body. They may also suddenly and violently strike out with the forefeet or kick out with hind feet. The syndrome is thought to have some physiologic similarities to Tourette's Syndrome in humans.

The behavior is most common in young stallions but may affect geldings and mares too. Usually there has been a major change in management or period of increased stress prior to the development of this behavior.

The main treatment is radical changes in environment and management that favor foraging and increased social/herd behavior. For stallions, gelding may be helpful. Feeding of free choice long-stem hay, along with companionship in the form of other horses or goats may be helpful. Pasture turnout is ideal.

For horses that do not respond to these management changes, certain tranquilizers and anti-depressant type drugs may have value. Occasionally, euthanasia is the only humane option.