Chomp! Incisors lock onto the edge of the board, and the horse arches his neck as he inhales. You've caught a cribber in the act. This horse is practicing what is known as a stereotypic behavior. Behaviors such as cribbing, weaving, and stall-walking might appear as nuisances, but behaviorists estimate they're seen in 10-20% of the population of domestic horses. Such behaviors can become problems, as they can affect a horse's well-being and his serviceability as an equine athlete. They even can render him unfit for use.
Although these behaviors have bothered horsemen for centuries, little research has been conducted into this area. Most studies have been funded by racing interests, because stereotypic behaviors often affect racehorses.
These are learned behaviors. Carolyn Stull, PhD, University of California, Davis, defined them as "stereotypic behaviors that are repeated without any apparent or obvious purpose or function. Such behaviors involve a need-related drive that develops in an environment with inadequate opportunities for satisfying the need. Once established, a stereotypic behavior may become a need in itself."
Also called a stereotypy, this behavior is relatively invariant. The animal repeats the sequence over and over.
Behaviorists observe many types of stereotypies practiced by domestic animals and wild animals in captivity. Horses uniquely indulge in the oral-based stereotypy of cribbing or crib-biting.
A cribber hooks his incisors onto an object, such as a fence rail, post, door, feeder, bucket, or any other item he can grab. Grasping a surface with his teeth, he drops his lower jaw and opens his throat. He arches his neck, pulls backward, and completes the act with a belch-like sound.
In popular definitions, some cribbers are called windsuckers, because they appear to suck air with or without grabbing an object. You might hear that windsuckers swallow air, called aerophagia, but a recent study in the United Kingdom showed this to be incorrect. "Radiographic and Endoscopic Study of Horses Performing an Oral Based Stereotypy," by Paul McGreevy, et al., described crib-biting/wind-sucking as "an oral-based behavior frequently involving the horse grasping a fixed object with its incisor teeth and engulfing air with an audible grunt." McGreevy used fluoroscopy and endoscopy to observe air entering the pharynx and esophagus. This air was not swallowed into the stomach.
Cribbing differs from the locomotor or ambulatory stereotypies, in which the horse moves in a constant, repetitive rhythm. A weaver will sway in place on his forehand, usually in the same location in his stall. He might shift his weight from one foreleg to the other, rocking from side to side on his front feet. Some will lift the forehand and swing head, neck, and forefeet like a helicopter. Or he might bob his head up and down.
Weavers can develop physical side-effects from their actions, since they are putting stress on leg joints. Certified Farrier Philip Johnson noted that a weaver widens its stance. "This can lead to ringbone and knee problems," he said. "They tend to get ringbone on the inside edge of cannon bones, and the toes of their shoes wear out sooner."
Other locomotor behaviors are stall walking and kicking. These are less common problems, with another McGreevy study ("Management Factors Associated with Stereotypic and Redirected Behavior in the Thoroughbred Horse") reporting 48 weavers out of close to 3,000 Thoroughbreds surveyed.
The walker circles constantly in his stall. The kicker pounds his hind feet against walls, either to hear the sound, expend energy, or attract attention. Johnson noted that kickers display hock problems, due to hyperextension of the joint.
Some horses engage in the injurious behavior of self-mutilation. They nip and bite themselves, usually in the flank area.
Such ingrained habits can impair the horse's soundness, or his ability to perform as an equine athlete. Occasional behaviors might not affect his health or concern you. Chewing wood or gnawing on a metal door frame doesn't mean a horse will become a cribber. Sporadic head-bobbing might not intensify into actual weaving; and excited movement isn't the same as non-stop walking. But if you notice that an infrequent behavior has escalated into a habit, you might need to explore ways to redirect behavior.
Stable managers label these behaviors as stable vices, because they consider a vice as a defect in personality. The animal behaviorists who contributed to this article consider them problem behaviors. Dr. Joseph Stookey, Associate Professor, Western College of Veterinary Medicine, University of Saskatchewan, noted, "A stereotypy is a clue that something is not quite right."
Some equine experts do label stereotypies as unsoundnesses. Sue McDonnell, PhD, University of Pennsylvania School of Veterinary Medicine, New Bolton Center, explained, "It's a matter of opinion (depending on the type of problem, type of use of the horse, etc.) whether or not these behaviors render the horse unsound."
These animals can endanger people, because the horse indulging in his stereotypy isn't dependable. You can get stepped on or kicked if you intervene in the stall.
Don't Fence Me In
The horse is an animal of action. He is alert and active 12 hours a day, drowsing about five hours and sleeping seven.
In his natural state, he uses his mouth and feet to meet his needs for eating, socializing, and avoiding danger. He spends 70% of his time grazing. With his mouth, he takes small bites of grass. With his feet, he walks and grazes, walks and grazes--ranging across the environment while he forages. He relies on his feet to stay close to his companions and also to run from danger, or to kick or strike.
Domestication limits the horse's space. The domesticated horse has to be in place, to make him accessible for his job of athlete, worker, or pet. Fences or walls confine him to a limited area, and they often separate him from equine companions. His feed is indigenous or supplied from outside sources.
Humans decide how to manage the horse's life--where he lives, what he eats, what he does. Humans expect animals to behave politely, accepting human dictates without objection. The energetic athlete is expected to perform with nerve, then quiet down and stay put.
Domestication also determines the horse's heredity, as most horses are the result of planned breedings. Today's horse is the product of dozens of previous generations that lived under human management. Genetics influence how he reacts--how he expresses the species' needs through his mouth and feet.
Animals adjust to the human-controlled environment in different ways. Some withstand barn life better than others, but some horses do object to spending many hours alone.
A horse's inherent emotional makeup is cultivated by management. Early in life, he learns behaviors that he repeats as habits. Some, and maybe all, animals are prone to stereotypies, just like humans tend to show certain behaviors when frustrated or bored. No existing evidence links stereotypies with particular breeds, although such behaviors are associated with bloodlines.
"It's a genetic predisposition to show stereotypic behavior," said Katherine Houpt, VMD, PhD, Diplomate ACVB, Cornell University. "To see whether a horse is likely to crib, see whether his sire or dam or half-siblings do it. Most horses that show one kind of stall vice will have relatives that show another."
Stereotypic behaviors are seen in the light horse breeds, with fewer noted in other breeds. McDonnell noted, "Ponies are not as prone to developing stereotypies. Draft horses play with water, and I've seen a few that weave. They seem to have a higher threshold."
In order to prevent your horse from developing a stereotypic behavior, it's important to understand potential causes. The domesticated horse can experience frustration when you expect him to adjust to your environment.
Janice Swanson, Kansas State University, said, "Some things tell you as an observer of horses that they have certain needs. If their needs are not met, they have coping mechanisms." Such behaviors can be self-rewarding, and the horse develops a habit.
The exact causes remain unclear, although stereotypic behavior seems associated with the time the horse spends in the stable. Stable management can fuel his habits. Swanson explained, "We're dealing with a human behavior problem. It's your responsibility (to cope with the horse's needs) with housing arrangements, feeding patterns, types of roughage, and the horse's opportunity to be turned out during the day. Altering your management practices does require you to be involved."
Recent studies have looked for relationships between specific management practices and the incidence of stereotypies. Authorities list a range of possible causes, including the effects of weaning (and early weaning), training, feeding, housing, and social contact. These reports cite the percentages of horses with stereotypies from 5-25%. However, it hasn't been proved that a stereotypy has a function and helps an animal deal with stress.
In his apportioned space, the horse can feel alone and anxious, isolated from other horses. If you treat him like a convicted felon, enclosing him in a dark stall for 23 hours a day, he's likely to display problem behaviors.
"In general, you can say the more enriched the animal's environment is in terms of social contact, the less intense the stereotypy," said McDonnell. "We all know that when you separate horses, it provokes a state to where they're more likely to exhibit a stereotypy."
Change can spark problem behavior. McDonnell blamed abrupt changes in a horse's environment, particularly his social environment, for some of these problems. "Change provokes the state leading to stereotypy and frustration."
Stull said, "The longer a horse is bored or has no penmate or no social stimulation from other horses or humans, it (the behavior) becomes more frequent." She added that enforced stall rest is difficult. "Even if resting, he should still be able to see his neighbor. With a horse under quarantine, he still needs human contact, such as being brushed several times a day."
Some horses are more nervous, with an abundance of energy. They can experience frustration at a lack of space, or boredom due to lack of external stimulation.
"What horses do affects the incidence of cribbing," said Houpt. "Surveys show that endurance horses seldom show it, while dressage horses and racers do. It's those who spend most of their time in stalls."
Stookey has filmed racehorses in their stalls. From viewing the videotapes, he noted, "Just about every horse does something in the stable. Part of that is genetic, because they are high-strung animals."
The horse's diet and feeding schedule are blamed for stereotypic behaviors. Swanson said, "Horses are grazing animals. What we come down to by looking at other animals, it has a lot to do with feeding. Horses need to graze all day. You can manage vices by looking at your feeding routine and exercise."
A horse can experience a nutritional deficiency through a diet that's high in energy and low in fiber. Many people blame grain and pellets, especially sweet feed, and suggest switching to hay to increase roughage. McGreevy's study reported greater numbers of abnormal behavior with horses fed less than 6.8 kilograms of forage a day.
Stookey has studied other confined livestock for behavior problems, such as swine who practice bar-biting. He pointed out that restricted feed intake is a cause, more than confinement and restricted movement. "Bulk up the diet and give more feed a day, to reduce stereotypies. We know that most of the oral stereotypies are related to hunger. They develop over time, before they become a fixed pattern. It seems if an animal is not satiated, it tries to take moves or motions that normally would allow it to eat. If it's not able to eat, it repeats that motion."
He explained how thwarted feeding behavior can cause a stereotypy like cribbing. Normal behavior includes the appetitive (from appetite) phase and the consumatory (eating) phase. The animal gets into position to complete the motions of the appetitive phase, and when thwarted, again starts the position that leads up to the motions.
You might notice when your cribber practices this behavior. He might crib around mealtimes, waiting to be fed, or when other horses eat. Anticipating your actions, such as when you turn him out or bring him back to the barn, can also spark his cribbing on the stall door or paddock gate. Your horse might even relish an "after-dinner" cribbing session.
Stookey added that weaving could have a similar cause. "It could be the first step toward foraging, or to get to a companion. Moving is a behavior that's thwarted, and the horse tries to start the movement again. He tries to go toward feed or another horse." The horse's excess free time in the stall might allow stereotypies to develop, as he's unable to search for food through movement and go through the oral motions of the appetitive sequences.
Young horses are at greatest risk to developing stereotypies. Often a youngster which starts this behavior tends to practice it throughout its life. Authorities note that older horses are much less likely to develop such problems.
Stull mentioned that a weanling would be less likely to develop a stereotypy than a slightly older horse. "With any kind of long-term confinement for a young horse, you look at a higher risk for stable vices. They have a need for exercise and a need for social comfort. A susceptible horse would be a yearling to four years old--after the age of four, they have more of a work schedule."
Many horsemen contend that horses learn these behaviors by observing and mimicking stablemates. If you own one of these horses, you probably know the feeling of your horse being treated as a leper in the barn.
Stull said that cribbers do learn through mimicry. She would advise a manager to bar cribbers from a boarding barn, and noted that a group of young horses would be candidates to pick up the habit from a chronic cribber.
Swanson said, "The jury's out. You can argue both ways about how these behaviors develop. Is it spontaneous, or does the horse mimic his neighbor? We don't know."
According to Stookey, "It's never been shown scientifically if that is true. You could set up an experiment, where you put a weaver next to a horse that doesn't weave. However, whatever environmental stress that was present to begin one horse weaving would affect other horses, too."
McDonnell noted that she feels horses rarely learn bad behaviors from others. "It's very hard to prove one way or the other. Do environment events that induce the stereotypy in one animal simultaneously cause it in others?" At the Equine Behavior Lab at New Bolton Center, she has housed "normal" horses "in a barn of stereotypy-prone animals. The behavior didn't prove to be contagious."
The Self-Destructive Horse
A behavior can develop into a problem that threatens a horse's life. McDonnell noted that the New Bolton Center houses horses donated for euthanasia, due to their stereotypic behaviors.
Some authorities have described how animals display a fascination with the behavior, and they compare these horses to human drug addicts. They cite the increase in endorphins, which are peptides that occur in the brain. These naturally occurring, opiate-like compounds are believed to reduce pain and modulate mood and response to stress.
Recent research argues against the addiction theory in all types of animals. Endorphins remain a subject of debate, with no one proving that the horse practices a stereotypy to get an "endorphin" reward.
McDonnell noted that scientists can't conclude that the horse seeks a "fix." She said, "We know that endorphins rise when the horse is exerting stereotypic behavior. If you match up the blood results with the behavior, you could easily conclude in long-term stereotypic animals, that they work to a high. A weaver gets very intense at it, when endorphins are at a low level. When the endorphins correspond to a high level, the horse stops, and they drop down again."
Houpt said, "If you give the horse a blocker of endorphins, it stops the behavior, but it starts up again. They may be involved in starting the behavior, but it's not that the horse gets a high."
Stereotypic behavior is counter-productive, in serious cases affecting the horse's willingness to work. The problem can affect trainability and rideability, so it becomes an economic disadvantage to most horses. However, some great athletes have exhibited stereotypies--Thoroughbred champion John Henry is a cribber.
Such horses can change in physical appearance. A cribber might crib instead of eating. This horse is often termed a hard keeper, as he consumes less feed and becomes thin. His upper incisors show evidence of his habit. Some wear their teeth down to "buttons," and others have teeth that are misshapen--slanted at a more forward angle due to the repeated pulling on objects. A weaver or stall walker can lose condition.
Some cribbers might look bloated. Stull explained, "The muscles on the abdomen and esophagus become more developed. The muscle on the back appears disproportionate."
The cribber contracts neck muscles, and this action can thicken the neck. As the horse arches his neck, he contracts the sternocephalicus and sternohyoideus muscles on the throat.
Cribbing has been blamed as a cause of colic, with the horse appearing to suck air. However, McGreevy used fluoroscopy and endoscopy to observe air entering the pharynx and esophagus. This air was not swallowed into the stomach, which suggests no link with tympanitic colic, or the gaseous distension of the intestines.
The behavior of self-mutilation, where the horse repeatedly bites his flank, can definitely detract from the animal's appearance. McDonnell noted that it appears to resemble the actions of two stallions meeting: "Some suggest it's self-directed, intermale aggression. Two stallions will pay a lot of attention to big, long sniffs, going nose to nose, nose to tail, investigating the flank area, stomping, and nipping at the flank." She added that she also sees self-mutilation in geldings, and up to 25% of self-mutilators she has seen are mares.
Whatever the stereotypy, the person selling a horse should declare any problems to a horse's purchaser. Stull recommended, "It's the ethical responsibility of the seller to tell the buyer. It could limit the horse's usefulness and impact the welfare of that horse, depending on where you're taking it." She said that this was especially important for a first-time buyer, who likely intends to board the horse. Because a boarding barn might ban cribbers, this can discourage the novice owner from continuing an equestrian pursuit.
Changing the Stimuli
The horse's behavior should prompt your stable management. Yes, you can simply ignore a nuisance behavior, but most horse owners take action.
First, rule out physical causes by having a veterinarian check the horse's general condition and well-being. McDonnell advised, "Once a stereotypy is identified, be sure the animal is in good health, with no gastric ulcers, skin problem, pain, or head, ear, or eye problems. Be sure the diet is free of anything that might cause metabolic disorders that can provoke stereotypies."
You can attempt to control stereotypies by preventive or corrective action, although you'd be wiser to prevent such habits. Curing a horse's stereotypic behavior can be a difficult task.
Stull suggested, "If you see a horse starting a habit, re-evaluate your management scheme and ask, 'What should he be getting that he's not getting.' A stereotypy is a flag to management."
Prevent stereotypies by meeting the horse's needs. You are responsible for providing a stress-free environment that doesn't induce such behavior.
"Evaluate on time-lapsed video the environmental events associated with normal and abnormal behavior," said McDonnell. "Sometimes factors can be identified and manipulated so as to minimize the stereotypy."
Enrich the horse's environment by designing for his needs. A stall's construction should provide contact with other horses. Minimal contact has been associated with increased abnormal behavior; visual contact between stall interiors has been associated with less abnormal behavior.
Through open partitions of bars or grille, each horse should be able to see his neighbors, and also to see activity in the barn aisle or shedrow. Stall design should permit social contact among compatible horses, the option to touch and react. "Horses really bond with neighboring horses," said Stookey. "If they are side by side, each horse will work out the arrangement. One will back off, so he doesn't get chewed up by his neighbor."
Changing a horse's environment can redirect the behavior of a horse which is developing a stereotypy. Most stereotypies disappear when the horse is removed to an improved environment. Turnout to a larger space or moving the horse to a different site can keep him exercised and amused.
Houpt noted, "The incidence of cribbing, its frequency, does seem to be made better by putting the horse outside so he can graze. A small percentage of horses react to stall confinement by developing stereotypies. They don't show it as much when put outside, so that is a response to change."
The regular turnout might change a horse's actions, except with those with a confirmed behavior. Many self-mutilators, however, bite themselves only when turned out. Stookey said, "With horses, it's interesting that the stereotypies don't disappear when they're put on pasture. Flank-biters are still seen when you open up the environment." Close confinement in a tie stall can restrict this behavior.
You can also divert attention from a stereotypy. Give a horse companions, such as a goat or quiet pony in its stall, a buddy to help keep the horse moving.
Giving your horse something else to do might not meet his needs, but it can refocus his attention. Realize that some diversions can be anthropomorphic, where you provide an acceptable alternative to the "vice."
Unsupervised play redirects energy. "The horse really needs to let out all of that pent-up energy," said Sandi Budman of Horseballs, Ltd. She cited a customer from Germany who reported success in diverting cribbers by giving horses Horseballs, and others who have barns where horses play with the balls at night. "If a horse is thinking about cribbing, he forgets it with the noise of the balls flying in the stalls."
Stull approved of toys. "Probably the most important management of toys is they have to be unique, such as Horseballs and hanging toys. You have to have an assortment of toys, so you change them every couple of days. Some horses tend to play with them more than others."
Feed changes can control stereotypies, feeding closer to the horse's natural pattern of grazing. Stull suggested, "I would try to keep long-stemmed hay in front of a horse, if he showed the first indication of cribbing. Usually they start cribbing on the door to get attention. I suggest that you put the hay in front of the door."
Stookey recommended increasing the amount and type of forage. "One study noted 14 pounds a day, and you see a lower instance. It also has to do with the quality of forage. Feed lower quality and more of it, and you reduce the instances."
He added that stable managers don't like to see horses develop hay bellies, but the horse needs to fill up on hay. "In order to meet the daily nutrient requirements, the horse is required to take in a great deal of forage. A lower quality hay will assuage the horse's appetite."
Feeding grain increases the likelihood of stereotypic behaviors. McDonnell feeds no grain to the horses she's studied, those with stereotypies that made them candidates for euthanasia. She explained how she "jolts" these serious cases into another feeding pattern. "I put them on a medium quality grass hay. They get so hungry that they'll eat the hay, and they spend the same amount of time eating that they would graze out on pasture."
Feeding frequently helps the horse to feel satiated, to reduce the feeding motivation. "We feed them at 12, 3, 6, and 9, in the stall. They adopt a pattern we call stall grazing--take a few bites, take a few steps. They have to eat all the time. I like them to eat off the floor and move around in a more physiologic pattern."
McDonnell added that changing to a timothy, or timothy/orchard grass mix, has helped some patients return to a normal pattern of behavior. "They may still have the stereotypy, but clinically they become more normal horses and they start to put on weight."
Another change would be modifying the stall to try to discourage chronic behavior. You can erect barriers by removing likely sources of cribbing. Cover wood surfaces with metal, or treat wood with foul-tasting substances formulated to repel wood chewing and cribbing. Add a V-shaped stall yoke above a stall door, to discourage weaving. This might not stop him, because he can still shift weight from foot to foot. One study showed that straw bedding was associated with less weaving.
Punishment is another correction, with varied results. The dedicated cribber might only cease his behavior when fitted with a restrictive device. Fitted snugly, the cribbing strap inhibits the act. It exerts pressure and causes discomfort when the horse arches his neck to crib. Some owners report success with a recent product, the Miracle Collar, as an alternative to the traditional cribbing strap.
To disrupt the locomotor stereotypies, controlled studies have treated horses with L-tryptophan. "It was extremely effective," said McDonnell. She noted that this medication involves minimal expense and is readily available; grass hay is naturally higher in this substance than other hays.
McDonnell has been asked how to rear a horse which would be less likely to develop a stereotypy. She suggested teaching the young horse to accept change. "Raise a horse to go everywhere and do everything, by providing him with different situations. Introduce situations to him early, such as a variable feeding schedule, so he learns to accept change."
She contended that adhering to a strict routine binds the horse to rituals. The horse which has never experienced abrupt change has trouble accepting a sudden variance.
To remove all stereotypies, the only true solution would be to return all horses to a natural state. More realistically, you can manage the incidence of such behavior by modifying your actions to meet the horse's needs.
About the Author
Award-winning writer Charlene Strickland lives in Bosque Farms, N.M. She has published 8 books and over 600 magazine articles, and is a member of the International Alliance of Equestrian Journalists.
POLL: University Equine Hospitals