Horse owners have plenty of equine vices to be concerned about.

Most habitual behaviors take more of a toll on the horse, the stable and the owner’s nerves than on the owner. Stall-walking, cribbing, weaving, pawing, kicking the stall walls at feeding time and the other idiosyncrasies horses develop over time are generally related to too much confinement, boredom, or a sense of humor simply not appreciated by the humans in the horse’s world. My horses have now all taught each other to lick the stall doorjamb after a grain feeding. They also all—including the mini who has to stand on tip-toe to do it—remove their halters and leads from the hooks next to their doors and throw them into the middle of the aisle each morning in a kind of equine roll call.
But the minor vices don’t hold a candle to the Big Three:
Biting is at the top of the list because it is insidious, difficult to cure, and very dangerous to everyone working around the horse.
In the horse world, biting is a way of dominating herd mates. Most horses respond well to each other’s body language, so outright attacks are relatively unnecessary. Horses are far more attuned to minuscule movements and body positions than are humans, and they understand herd dynamics. Stallions will bite mares during breeding and other stallions during a fight for control of the herd. Mares will bite each other when there’s a question of who stole whose boyfriend. They will occasionally bite their offspring if there’s good reason for that strong a reprimand.
But some horses learn early on that humans are easily frightened and that control can be wrested away from them by a show of teeth. It may start as a nip on the shoulder or side when the girth is too tight or saddle fit is poor and causing pain. It may start as a means of getting attention. The horse who sticks his head over his stall door and reaches out for you as you pass may accidentally grab your shirt once. If you stop and talk to him, he may grab more than your shirt the next time. It may result from a battle—real or perceived—over personal space. Some horses have learned not to trust strangers and are not happy when one pokes his body into the stall without invitation.
Sometimes it’s accidental. One of my favorite horse stories involves a friend who was hanging out with her horse in the pasture and didn’t notice a rival mare approaching from behind her. Her horse, figuring the herd mate was out to grab his cookies, reached around and snapped. Unfortunately his owner’s butt was between him and his target and firmly in the blind spot directly in front of his face. She sported a horse-mouth shaped wound for weeks.
Accidental bitings generally reflect a human lack of good judgment. Those don’t often recur. It’s the aggressive biter who is most dangerous, and that is the most difficult type of biting to cure.
Rule number one would have to be Don’t Buy a Horse that Bites. Barring that, the next rule has to be Don’t Put Yourself in Harm’s Way. If you know your horse has developed a penchant for the taste of polyester, train him to stand cross-tied and always tie him firmly before you start grooming or tacking up. Eventually he will give up the habit on his own.
If he is an aisle-way attacker, find a way to close up the top of his stall. Stall screens are available, and many barn owners will be pleased to allow you to mount one if it means less bloodshed and fewer barn hands quitting due to injury. If he bites when you try to catch him in the pasture, don’t do that. Run him into an enclosed space or have him left in his stall when you want to ride.
The electronic training collar works wonders for biting. My mini stallion is now convinced that his herd mates all have electric hindquarters, and he avoids them instead of taking chunks. Though no one actually likes the thought of hitting a horse, a well-timed and swiftly-delivered smack with a crop will sometimes be enough to convince the biter you are not to be messed with. It is not true that hitting a horse on the nose will make him head-shy. If it were, my youngest would require anesthesia for bridling. He doesn’t bite anymore. In fact he approaches a hand-fed treat with his “gentle” mouth—wide-open, tongue thrusting, and eyes closed. No harm, no foul. The trick with any kind of punishment is to keep your anger at bay. This is not about revenge; it’s about training.
The aggressive vices are not something to be treated lightly. If you cannot find a way to prevent or cure biting on your own, don’t hesitate to call a respected professional. The life you save may be your own.