What causes a horse to bite?  Like most aggressions between horses, there are more bite threats than actual bites, because horses deftly learn to respond to each other’s subtle warnings.

Generally horses at will, given enough space, will flee or avoid aggressions more serious than threats.

What we call bites can range from nips where the teeth are only slightly parted to grasp the victim to bites in which the teeth are widely parted and can result in both skin and crushing injuries when inflicted on a human.  Reported injuries to people due to horse bites are less common than from dog bites and less common than other injuries from horses, such as kicks and falls.

Here’s a list by Pennsylvania based Dr. Bonnie Beaver, a veterinarian and behaviour researcher, of the types of aggression shown by horses:  Fear-induced,  Pain-induced,  Irritable,  Dominance,  Inter-male,  Sex-related,  Play,  Protective,  Maternal,  Redirected,  Learned,  Self-mutliation.

All of these can include biting and most can be described both in terms of horse-horse aggression and horse-human aggression.  If we can understand why a horse is biting we’re better equipped to stop the behavior.

Probably the most sustained horse-on-horse aggressions that include a lot of biting are the inter-male interactions.  Harem stallions confronted with a challenging bachelor male for example will go through ritualized posturing and threats, which might lead to outright fighting that can go on for quite a while.  Dr. Ron Keiper, who watched the Assateague ponies for many years, saw stallions die apparently from infected bite wounds.

Probably the worst nippers and biters toward people are stallions.  This might be the testosterone talking, but it also might be complicated by other factors.  We sometimes see redirected aggression when a stallion can’t get to another stallion or to a mare.  And other times handlers encourage stallions to be fired up based on the belief they need that to breed successfully.  Further, stallions’ natural aggressive tendencies might not have been successfully contained by handlers so they learn how to successfully land nips and bites on people.

Many episodes of biting by any horses toward humans have a strong element of learning behind them.  Horses can learn to delay or stop certain unwanted, annoying, or painful stimuli induced by humans by using aggression.  For example, take from the list above fear – and pain-induced and irritable nipping and biting.

First, humans are probably not quite as good as other horses at reading signs that the horse is troubled or making subtle threats.  If a horse resorts to a bite to stop something a person is doing that they don’t like, and they are successful, then they’ve learned that biting works.

We should always consider, too, how horses evolved to live in relatively stable harem groups, in wide open spaces, with food resources plentiful and scattered.  Bringing horses into confinement reduces their ability to leave rather than fight, and often causes them to regularly re-establish some kind of dominance hierarchy.

Add in a person doing purposefully or, more often, inadvertently aversive things that a horse can’t escape, and it’s not surprising to see biting and other aggression from the horse toward the human.

Biting is very dangerous behaviour, and it might be best to consult a professional for advice or assistance.  Some horses seem to bite with no clear current cause or history of provocation (though we often don’t know much of a horse’s history).

Biting can be one of the hardest things to train out of a horse.  Initial efforts should be about taking the horse out of the bite provoking situation.  You can train a horse to stand and do something else (like target) at a bit of a distance until you can get further control of his head.  Once you have established effective control of his head, you can further use reinforcement training to try to eliminate the biting behaviour.  This might include reducing the pain associated with a treatment, rewarding his compliance with a mildly painful procedure, having a physical examination carried out to find a source of pain, or rewarding behaviour alternatives to biting.

If one has to resort to punishment for biting, it must be exceptionally swift following the bite or bite threat, and it has to make contact with enough severity to impact the horse.  Frequent misses will most likely teach the horse to be more successful at the next bite and retreat.

One note about using treats in positive reinforcement training:  It’s true that giving treats by hand can teach horses to hassle, nudge, nip, and bite.  However, with positive reinforcement, a horse has to do something in order to earn a treat.  The first step in the training process is “you turn your head away from me to get a treat.”  It’s easy to teach and helps avoid nudging, which can escalate into nipping.