The barn is quiet as contented horses clean the last of their evening feed from their buckets. Then a sharp sound—something between a grunt and a burp—breaks the peace. A horse is starting to crib. With his teeth firmly anchored on the edge of his stall front and a faraway look in his eyes, he arcs his neck, presses down and sucks air into his throat with that distinctive grunt—again and again and again. Why?
“He isn’t doing it to annoy you,” says Katherine Houpt, VMD, PhD. Cribbing is one of many bizarre behaviors that have puzzled people for centuries. In this article Dr. Houpt helps explain what’s known about the reasons behind the behaviors and what you can do about them. The former director of the Animal Behavior Clinic at Cornell University, she now heads her consulting practice in Gaylord, Michigan.
The old-time term for these behaviors, stable vices, implies a sneaky intent on the horse’s part. Nothing like that is involved, research by Dr. Houpt and others has helped to show. Some so-called stable vices are stereotypic behaviors (stereotypies)—repetitive actions that serve no useful purpose for the horse. Others may be attempts to deal with discomfort or with some condition in the horse’s environment. It’s important to remember that unusual behavior can often have a physical cause. Pain can make a horse agitated or cause him to kick, wring his tail or stand oddly. Neurologic problems can cause him to tilt his head or press it against the wall. If your horse shows unusual behavior like that, you should consult with his veterinarian.
Stereotypies: Just Gotta Do It
So far there’s no evidence that stereotypic behaviors originate from pain or disease. The most common stereotypies fall into two types—oral and locomotor.
Cribbing is the most common oral stereotypy; by some estimates about five percent of horses are affected. Stall boards, mangers and fence rails are favorite cribbing spots, but dedicated cribbers will latch onto whatever they can. In windsucking the horse performs the same throat action without holding onto anything. Other oral stereotypies include repetitive lip and tongue movements.
Weaving is a locomotor stereotypy; a weaver stands in one spot and rocks side to side. Others in the locomotor group include stall- or fence-walking (pacing back and forth in the stall or along a fence line) and circling endlessly in the stall. Kicking can be stereotypic or not. A horse may kick his stall wall in a show of antipathy to the horse next door; that’s not a stereotypy. If he kicks rhythmically and repeatedly whether there’s a horse next door or not, that could be a stereotypy.
Horses that perform these behaviors are highly motivated to do so, Dr. Houpt says. In her research she found that cribbers will work as hard to find opportunities to crib as they will to get food. “Weavers are just as motivated as cribbers, although the triggers for oral and locomotive behaviors may be different,” she says.
Why do horses perform these strange actions? There are more theories than firm answers. It was once thought that horses learned to crib or weave by copying others, but that’s not the case, Dr. Houpt says. Horses can learn from each other, so a horse stabled next to a cribber may be more likely to crib than another—but only if he’s predisposed to the behavior. Researchers now think a range of factors may be involved, among them:
Genetics: Cribbing and other stereotypies are most common in Thoroughbreds, followed by Quarter Horses (many of whom have a lot of Thoroughbred blood). “Arabians rarely crib and Standardbreds practically never do,” Dr. Houpt notes. The tendency to crib can be inherited, so it can be passed along in certain bloodlines. “So far no one has located a specific gene for a stereotypic behavior,” she says, “but now that genetic sequencing has become so much better, it’s likely that a genetic basis will be identified.”
Weaning: “Cribbing begins at weaning, and how a foal is weaned is important,” Dr. Houpt says. “Foals that are weaned on pasture don’t crib; foals weaned on grain do.” The sudden influx of sugars and other soluble carbohydrates from grain feed may be a trigger.
Diet: Grain feed is often linked to stereotypic behaviors in adult horses, she adds, although the nature of the relationship varies: ”Horses often weave or stall-walk before feeding, while episodes of cribbing nearly always follow a meal.”
Opiates: One idea is that these behaviors trigger a release of endorphins and similar body chemicals, which are natural opiates. In this theory horses may start the behavior to relieve boredom or discomfort or for some other reason, and then they continue it to get an opiate reward. Supporting the theory, research comparing the brains of cribbers and noncribbers found differences in opiate receptors (areas on cells where the chemicals latch on) between the groups.
But this doesn’t necessarily mean that horses crib to get high. Opiates are involved, Dr. Houpt believes, but the nature of the involvement isn’t clear. “Different researchers have compared opiate levels in cribbers and noncribbers and come up with different results—sometimes levels are higher in cribbers, sometimes lower,” she notes. “My take is that the opiates may be released not by cribbing but by consumption of sugary feed. The opiate release stimulates cribbing, not the other way around.”
Stress and social isolation: Horses are herd animals, and horses turned out in groups seldom weave or show other locomotor stereotypies. Those behaviors may originate with the horse’s natural instinct to join a herd, Dr. Houpt suggests. Stress and isolation may not be direct causes of cribbing, but they tend to increase the behavior. “A horse stabled next to an aggressive neighbor is more likely to crib than one with a quiet neighbor,” she says.
Gastric distress: Several years ago British researchers found that weanlings who had started to crib had more gastric inflammation and ulcers than noncribbers. They wondered if horses start cribbing as a way to produce saliva, which buffers stomach acids and could relieve discomfort. So far a true cause-and-effect relationship hasn’t been shown, and in her research Dr. Houpt has found that cribbing doesn’t trigger saliva production. It’s just as likely, she says, that the mouth actions involved in cribbing stimulate the production of stomach acids, promoting ulcers.
If behaviors like weaving and cribbing may help a horse cope, should you try to stop them? There’s debate about that, but most of these behaviors have health consequences. A horse can go lame fence-walking, wear himself out circling in his stall or injure himself kicking the walls. Cribbing is linked to colic, both gas colic and a severe type, epiploic foramen entrapment, in which part of the small intestine becomes strangulated and can die. “That has convinced me that controlling these behaviors is important, especially for a horse that has colicked,” Dr. Houpt says.
The question is how. The longer a horse continues a stereotypic behavior, the more difficult it will be to control. You stand the best chance of stopping these behaviors when they are new, generally when the horse is young. Once he’s confirmed in his habit, you may not be able to eliminate it, but you can still take steps to minimize it.
Control cribbing. You may need to resort to several methods:
• Change the diet. “Increase roughage and decrease concentrates,” Dr. Houpt says. Sugary concentrates like sweet feed trigger the behavior. (Straight oats don’t seem to have the same effect, she adds, so oats may be a good choice for a cribber who needs grain to meet energy needs.)
• Try a cribbing collar. The collars fit snugly around the horse’s throat and interfere with the air-gulping action. They don’t prevent normal swallowing or interfere with grazing. There are many different types; you may need to try a few before you find one that works for your horse. The main drawback is that the collars must be quite tight to work, so they may cause sores.
• Try a cribbing muzzle. The muzzles attach to the horse’s halter; a metal grill or cage over the mouth allows the horse to graze or eat hay but keeps him from latching onto objects with his teeth.
• Increase pasture time. Turnout and social contact may help reduce cribbing and other oral stereotypies, although a determined horse will crib anywhere. “Horses may crib less when they’re out on good pasture but not in a dirt paddock,”’ Dr. Houpt says.
• Check out cranial electrotherapy stimulation. This treatment has been reported to help some cribbers, Dr. Houpt says. It uses a noninvasive device (the Happy Halter, from Fisher Wallace Laboratories) to deliver a low-amplitude electric current to the brain. The horse is haltered and held for each 20-minute treatment. Drawbacks are the cost of the device ($495) and the fact that the treatment must be given daily, although the manufacturer says there can be a long-term conditioning effect. (Dr. Houpt has tried the device for stall-walking and didn’t see a reduction in that behavior.)
• Consider surgery, which aims to stop cribbing by cutting the muscles directly under the throat and/or the nerves that control those muscles. Variations of this surgery have been done since the 1920s with mixed results. Surgeons at the Louisiana State University School of Veterinary Medicine have reported good success rates with a laser procedure developed there. However, the procedure is most likely to work in horses that have been cribbing less than three years and, as with any surgery, there’s a risk of complications.
Cribbing rings (hog rings), small metal rings implanted between the horse’s front teeth, were in vogue a few years ago but aren’t used much now. They cause discomfort when the horse tries to grasp an object to crib, so, while this method may be effective, some people consider it inhumane. The rings also tend to break or fall out and there’s a risk of gum infections.
There is no magic pill for cribbing. “We tried lots of drugs, including Prozac, and nothing worked,” Dr. Houpt says. Opiate blockers (drugs such as naloxone that bind to receptors on cells, preventing opiates from latching on) will stop it temporarily but are controlled substances with short-term actions and harmful side effects.
Manage weaving and stall-walking. People sometimes install bars, hang balls or put other obstacles in a horse’s stall to break up the repetitive patterns of weaving and stall-walking, but most horses just learn to evade the obstacles and continue. Since the root of these locomotor stereotypies is the need to be in a herd:
• Turn the horse out in a group as much as possible.
• In the barn, make sure he can see horses and that his neighbors aren’t aggressive.
• Distract him with a mirror. A few years ago, Daniel Mills, a professor of veterinary behavioral medicine at the University of Lincoln in Britain, reported that he could reduce weaving by an average of 97 percent by placing a specially designed mirror in the stall.
Outwit kicking and pawing. Kicking and pawing aren’t always stereotypic behaviors, so try to determine the cause:
• Is he pawing because he’s sore? If he paws a hole in his stall floor and stands in it, he may be trying to redistribute his weight to ease discomfort. (Dr. Houpt says she has seen this often in Standardbreds.) The soreness may be subtle, so ask the vet to examine your horse.
• Is he kicking because he’s mad at the horse in the next stall? Move him or move the neighbor.
• Is he kicking or pawing because he wants food? This is a learned behavior: He acts up at feeding time, gets his meal and figures that his actions caused you to feed him. Correct him with counter-conditioning, Dr. Houpt suggests: Stand in front of his stall, wait until he stops and then (only then) give him a handful of feed. Do this consistently, gradually increasing the time that he must stand quietly before getting his reward.
• Is he kicking or pawing rhythmically and repeatedly regardless of the situation? Treat this like a locomotor stereotypy. Turn him out as much as possible. When he must be in, make sure he can see his (friendly) neighbors. If necessary, you can pad a kicker’s stall to reduce noise and the risk of injury. Kicking chains and similar old-time remedies are as likely to cause injury as to stop the habit, Dr. Houpt says.
When it comes to puzzling behaviors, horses have a broad repertoire. One horse gnaws fences. Another pins his ears and lunges at anyone who comes near his stall. A third poops in his feed bucket often enough that it seems deliberate. Actions like these aren’t stereotypies—they’re not repetitive (although they may be annoyingly frequent) and they seem to serve some purpose.
“Look at it from the horse’s point of view,” Dr. Houpt says. “What is missing from his environment?” If you can figure it out, you can probably get him to stop.
Wood chewing is distinct from cribbing because the horse eats the wood and doesn’t suck in air. It may have a physiological basis, Dr. Houpt believes. “Horses seem to chew wood mainly in cold, rainy weather, and I think the behavior may have evolved as a survival mechanism for horses in cold climates: Young tree branches served as a source of nutrition in winter when little forage was available,” she says. “It’s not needed now, but some horses still have the urge.” If yours does, you can offer a safe, nontoxic branch now and then in the hope that he’ll prefer it to your barn or fence.
Lunging or charging aggressively when people pass the stall may be a territorial response. “Horses aren’t generally territorial,” Dr. Houpt says, “but in a confined space, especially a space where they’re fed, they may be more so.” Counterconditioning may help. One method is to stand in front of the horse’s stall until he stops the aggressive behavior and only then take a step back. If you repeat this, over time he may see that quiet behavior is a better way to get people out of his space. Or you can use a reward-based system (like clicker training) to teach the horse to back on command. When he has that down, ask him to back in his stall when you approach (and reward him when he does). He may learn to step to the back of the stall when you walk up.
Self-mutilation, in which a horse repeatedly bites his flanks, is more perplexing. “It’s sometimes considered a stereotypy, but research suggests it’s more likely to stem from underlying physical discomfort,” Dr. Houpt says. This behavior is especially common in stallions, and for them misdirected aggression has also been suggested as a cause.
Then there’s the horse that insists on pooping in his water or feed bucket. He’s not doing it just to make work for you, Dr. Houpt says, although you may be tempted to think so. But the reason remains a mystery. Is it a marking behavior, a way of staking a claim? “We just don’t know,” she says. You can try changing the bucket or moving it to a different place in the stall, but you may just have to resign yourself to cleaning it out.
This article originally appeared in the February 2015 issue of Practical Horseman.