Many horses are inclined to bite. It's an unpleasant habit that can result to injured fingers and bruises on any place your horse sneaks a bite. The habit of biting people is quite different from windsucking, cribbing or fence chewing. Horses can bite hard, resulting in serious injuries. Your horse might intend it as a sly or playful nit a bite can be quite harsh. Even though horses are grass eaters, they still have considerable strength in their jaws, and their teeth are surprisingly sharp. A horse that bites isn't just annoying, it can be dangerous!
Why Horses Bite
Horses bite for a number of reasons. In the pasture, they may bite in play, to defend themselves, their food or offspring, or to discipline a young horse or one lower in the pecking order. They may become impatient because they know that the handler will be handing out treats, or carrying treats in their pockets. A horse that is aggressive, or has a lot of pent-up energy may act out by biting. Stallions, in particular, can become dangerous biters. Beginners should not own stallions as they require tactful, knowledgeable handling.
Allogrooming—when horses groom each other, is another time when horses may nibble each other, especially along the top of the neck and withers. Imitating this behavior by scratching in these areas is can be a form of praise. However, your horse shouldn't be given the opportunity to initiate allogrooming between itself and its handler!
The biting habit can start when the horse is quite young. Youngsters, especially colts, tend to be 'mouthy' and explore the world with their mouths. But, what starts as cute and innocent nibbling on a sleeve can evolve quickly into ripped clothing, crunched fingers, bruises and teeth marks. So if you have a young horse, don't allow it to explore you with its mouth. It needs to learn to keep a respectful distance and not initiate any contact. This may mean that you don't feed any treats by hand until respect is a habit.
Many horses will nip if the girth or cinch is tightened too quickly or tightly. Your saddle may not fit well, and the horse will lash out in anticipation of the impending discomfort. Your horse needs to be confident that it won't be hurt as you are saddling up and riding. This means changing or re-stuffing your saddle, honing your riding skills, going slowly as you cinch up and not making your horse into link sausage by doing the girth up too tightly.
What Doesn't Work
The instinctual reaction when your horse bites you is to smack its nose. This isn't effective. In fact nip, smack, nip, smack can turn into a game for many horses. They dive in for the nip when you've let your guard down, and duck away from the smack. Even if you do get the timing right occasionally, the punishment isn't consistent enough to leave a lasting impression.
There are some fairly ugly methods of dealing with biting. Holding a nail so the horse pokes itself as it bites at your hand is inhumane. Likewise trying to splash hot sauce or bitter flavored liquid into the horse's mouth is a bad idea.
What to Do
Teach your horse to be obedient and accepting of having its mouth touched. With a halter on so you can hold its head securely, rub the inside of the horse's gums and lips with your fingers. Your horse will probably dislike this but work slowly, doing what they can tolerate and then retreat when the horse objects, then slowly moving your fingers further and further into the horse's mouth. Once the horse accepts its inner lips and gums touched, you can reach into the toothless bars of the mouth, to rub its tongue and palate. Your horse may try to reciprocate by trying to grab at your fingers. Be more assertive in making the horse stand quietly and accept your fingers. As you do this, of course, be very careful to keep your fingers from between the horse's teeth.
Another method is to teach the horse to target on an object. Horses that habitually nip have very active minds and need to keep busy. Clicker training is a good way to keep a busy mind occupied.
At all times, you need your horse to keep a respectful distance and not initiate contact, not even to rub its head or explore your pockets. If your horse is aggressive, you'll need to get the help of a professional trainer.