Equine Self-Mutilation Syndrome (ESMS) is a type of stereotypy like cribbing, weaving, stall-walking or lip-flapping. Stereotypies are chronic, invariant, seemingly purposeless behaviours, generally associated with compromised welfare.

In a typical self-mutilation episode lasting from a few seconds to several minutes, a horse may spin, bite at the flanks, shoulders, or chest while squealing, striking, or kicking. In more extreme cases horses may lunge into the wall, or even throw themselves to the ground. It is (thankfully) a rare disorder seen primarily in stallions, less so in geldings, and very infrequently in mares.

Some researchers have likened the condition to Tourette’s Syndrome in humans – a brain-based neurological disorder where individuals engage in intermittent, unpredictable, purposeless and involuntary sounds or movements called tics. Dr. Sue McDonnell, director of the Equine Behaviour Lab at the New Bolton Centre, identifies three types of ESMS:

Type I is an extreme behavioural response to physical pain, which can usually be resolved when the pain is alleviated. Conditions such as a twisted testicular cord, abdominal abscess, and gastric ulcers are typical culprits.

Type II, seen only in stallions and geldings, is a self-directed intermale aggression. The sequence resembles the meeting behaviour of two stallions, except that the stallion himself is the target of his own antagonistic behaviours. Unlike Type I, it has a slow onset and is not readily resolved.

Type III is a quieter, invariant, repetitive sequence of biting at various body locations. McDonnell describes a stallion who bit himself in a stylized circular pattern, at the same time, in the same location, and for the same number of repetitions, each and every day. Since stereotypies seem to be associated with an endorphin release in the brain’s reward circuitry, they become reinforcing in and of themselves and may continue long after the initial precipitator has been resolved.

Management strategies

The first line of defense is to discover any possible underlying physiological cause. Locating and alleviating the pain will generally end the self-directed aggression. McDonnell suggests 24-hour video surveillance, which can be played back in double-time to catch subtle behaviours and patterns that may not be evident during a veterinarian assessment. If there is an indication that the behaviour is pain-related, then one can proceed aggressively with veterinary diagnostics.

If your ‘gelding’ is displaying stallion behaviours, there is a slight chance he may be a cryptorchid (have an undescended testicle). Blood tests measuring testosterone and/or ultrasound can confirm or rule this out.

Type II and Type III ESMS can often be improved with management changes that more closely mimic the horses’ evolutionary design for movement, social interaction, and almost continual grazing. Contemporary stable management practices where social isolation is the norm and the diet is rich in quality and correspondingly sparse in quantity, contribute to the development of stereotypies by thwarting these basic ethological needs. Stallions, who are hard-wired to be responsible for a harem of mares, face even more environmental challenges in our stables of solitary confinement. Interestingly, neither ESMS nor any stereotypies have ever been observed in wild or feral horses. Even modest modifications such as allowing tactile connection between compatible neighbours, reducing or eliminating concentrates (which are a known trigger for stereotypies), or providing a small-holed haynet of mid-quality “pony hay” to increase foraging time can ameliorate some of these stressors (see this issue Thinking Outside The Box on page 40).

More Drastic Solutions

Castration: For self-directed intermale aggression, castration sometimes resolves the problem, but sometimes makes it worse. McDonnell notes cases where self-mutilation was initiated in normal colts after gelding!

Psychopharmacology: Drug therapies include tranquilizers, tricyclic anti-depressants, progesterone, and the nutritional supplement l-tryptophan. In combination with environmental modifications, some psychopharmaceuticals have shown modest success. Unfortunately, there is as yet no miracle drug that completely resolves ESMS.

Hope for a cure?

Sadly, most researchers and practitioners are not optimistic about a cure for ESMS. If the behaviour does not have a physiological source, McDonnell recommends applying the full arsenal of treatment possibilities simultaneously. This appears be more effective in interrupting the self-mutilation than systematically introducing changes one-step-at-a-time. For a more realistic and less discouraging outcome, owners need to approach ESMS from a harm-reduction perspective rather than hoping for a cure.