Behavior Problems of Horses

Aggression by horses toward people occurs mostly in stalls where the horse feels confined in a small space that is also easily defended. The varieties of aggression toward people include fear based, pain induced, sexual (hormonal), learned, and dominance related.

Some horses, especially young ones, play with each other while showing signs of aggression such as kicking and biting. Although benign to other horses, behaviors like these can be dangerous to people.

Fear-based aggression can be differentiated from offensive aggression by the horse's posture. A fearful horse tucks its tail and turns its ears to the side. An offensively aggressive horse lashes its tail and pins its ears back.

The first step in managing equine aggression is to identify the cause and, if possible, to remove it. Training and positive reinforcement to establish control over the horse are also used, along with desensitization and counterconditioning. Environmental management is important as well; good management should include the provision of sufficient resources such as space, food, and water.

Some horses are considered to have pathological offensive aggression; they attack other horses and people that are near them. These horses should be separated completely from people and other horses and have a poor prognosis. They can be managed like large zoo animals by using protected contact; there should always be a wall between the horse and a person.

Less severe aggression can be treated with behavioral techniques. Training the horse to back away from a person for a food reward (offered in a bucket, not from a hand) is a good start. The person should carry a crop for protection, in case the horse does attack.

Aggression by horses toward other horses is associated mainly with mixing unfamiliar horses that are establishing a new dominance hierarchy. Just as some horses are aggressive toward people, other horses are pathologically aggressive toward horses.

The first step in managing a horse that is aggressive to horses is to separate it from other horses and to keep subordinate horses away from dominant ones. Separation is achieved by solid walls or double fencing to avoid kicks through a single fence between the animals.

Horses should have sufficient resources. Desensitization (several weeks of management in which the horses can hear, see, and smell one another but cannot reach each other) is the best treatment approach, and the manager can observe the animals for friendly or hostile behavior.  

Selective serotonin reuptake inhibitors (SSRIs) can be helpful in some cases. Combining progesterone and an SSRI has been helpful.

Punishment should be avoided. In cases of sexually related aggression, castration and progestins (eg, medroxyprogesterone) can help. Adverse effects of such treatment should be weighed carefully, and the horse should be monitored closely.

Aggression by mares toward people is normal during the first few days after parturition. These mares are also aggressive toward other horses.

Maternal aggression is hormonally driven and usually wanes with time. Mares should become familiar with their caretakers before delivery and have minimal contact with other people after delivery.

No treatment is required in most cases of maternal aggression. Keeping the mare haltered and using a pole with a hook to restrain her is a safe way of ensuring that the foal can be examined.

When cribbing, the horse usually grasps a horizontal object in the stall (such as the water bucket or Dutch door) with its incisors, flexes its neck, and sucks air into the pharynx. Some of this air enters the esophagus and is pushed through the GI tract as the horse eats. The abdomen swells with air-filled loops of intestine. This situation can lead to colic—in particular, epiploic foramen entrapment.

Sometimes horses suck air without grasping any object; this behavior is termed "windsucking" (a term also used to refer to pneumovagina).

Feeding highly palatable food (eg, grains, molasses) is associated with cribbing. Horses are most likely to crib just after eating sweet feed. There are breed differences in cribbing: Thoroughbreds are the most likely to crib.

Cribbing is associated with confinement; however, once the behavior is established, it will persist even if the horse is turned out to pasture with other horses. In one study, 10% of foals 20 weeks old started to crib when weaned, placed in stalls, and fed grain, whereas those kept on pasture at weaning did not start to crib (1). Although many stable owners believe that horses can learn cribbing by watching other horses, rarely does that happen.

Cribbing can be diagnosed by discovering that U-shaped pieces are missing from fences and horizontal surfaces in the stall, and observing worn incisors and enlarged neck muscles in horses engaging in this behavior. Usually the caretaker directly observes the behavior.

Management should include decreasing grain, except for oats, and increasing hay in the diet. Managing horses on pasture can help; however, horses will crib on fences or, if the fence is electrified, on telephone poles or electric fence insulators. 

Providing toys and stimulation is also advocated; however, even though doing so can improve the horse's general welfare, it has little effect on cribbing.

Placing a strap around the horse’s neck behind the poll will mechanically prevent the horse from flexing its neck so that it cannot aspirate air. Alternatively, a metal basket muzzle can be applied, allowing the horse to eat and drink but preventing it from grasping objects to crib on. Some horses find a way to crib with the muzzle (eg, grasping a linear object such as a stick), and most horses seem to tolerate the strap better than the muzzle.

Keeping stalls free of horizontal surfaces and objects that the horse can grasp can help minimize cribbing.

A variety of surgeries involving transection of the accessory nerve and the strap muscles of the neck have been suggested to manage cribbing; however, the varying success rates of these procedures and their negative impact on animal welfare are major disadvantages. In addition, surgery can lead to scarring around the esophagus that makes it impossible to pass a stomach tube, which is a risk factor for horses that frequently present with gas colic.

Offering a sugar cube to a horse can determine whether it cribs. Sweet taste is the most common stimulus for cribbing. One hypothesis is that sweet taste leads to opiate release in the brain, as it does in humans and rats, and that opiates trigger cribbing. Opiate blockers block cribbing.

Like a horse that cribs, a wood-chewing horse grasps pieces of wood with its incisors but actually bites off a piece of wood and swallows it. The definitive cause of wood chewing is lack of roughage in the diet. Confinement, high-concentrate diets, and lack of exercise increase the incidence of wood chewing.

Horses on pasture typically spend 8–12 hours per day grazing, whereas confined horses spend < 3–4 hours per day feeding. Wood chewing increases in cold, wet weather.

Providing more and varied roughage or exercise can decrease the incidence of this behavior. Eliminating exposed wood and covering fence edges with wires and taste repellents can also help minimize wood chewing.

Horses ingest sand or dirt if their hay is offered on the ground. A horse that intentionally eats sand or dirt could be seeking a nutrient otherwise low in its diet, such as iron.

Ingestion of sand or stones can become a serious problem, because it can lead to intestinal obstructions. Prevention is accomplished by providing feed off the ground, in a rack or hay net.

Polydipsia in horses is similar to excessive drinking in dogs. It is more common in young horses. The most common sign is a wet stall due to frequent urination.

It is important to exclude medical causes (eg, diabetes insipidus).

Stall walking and weaving are repetitive behaviors that occur in confined horses, serve no purpose, and are hard to interrupt.

There are two types of stall walking: slow, silent circling and rapid walking accompanied by neighing. The latter is a sign of confinement distress, and the horse should be managed outdoors with a companion and a run-in shed for protection.

If stall walking occurs only when a neighbor horse is leaving, it can indicate a form of separation anxiety. Horses that quietly stall walk usually walk in circles in the stall and, when released to a larger space, such as a pasture or barn, might continue to circle in a small area. It is a compulsive behavior. Stress and anxiety, such as anticipation of a horse show or trailer journey, appear to aggravate the problem. 

Treatment of stall walking should focus on providing social contact and maintaining the horse with other horses on pasture. The horse's own image in a mirror or even a life-size photograph of a horse might be recognized as a herdmate and could solve the problem. Providing thick straw bedding and feeding more and varied roughage can be helpful. SSRIs might be necessary to control the problem.

Weaving (ie, lifting the legs and shifting weight and head position from side to side in the same spot)—essentially walking in place—is another compulsive behavior of stalled horses. It is almost always performed at the front of the stall, especially a stall with a Dutch door, or in front of a window. Giving the horse visual access to a horse in the next stall seems to decrease the behavior, or, if that is not possible, providing a large mirror in the stall in front of the horse can help decrease weaving.

Horses might kick the walls of the stall because of boredom, aggression, or frustration. A horse might kick in anticipation when food is visible but out of reach; when the horse is then fed, the behavior is reinforced. A horse might also be frustrated when it cannot achieve its goals (eg, exercise, mating, or social contact). Stall kicking could be a form of environmental stimulation.

Horses that kick and make holes in the walls of the stall might also eat wood from these holes. Treatment should be directed toward eliminating the underlying cause, which is frustration. The horse should be fed first so that it is not frustrated. If it kicks or paws 10 times and then its feed is delivered, it will kick or paw 15–20 times the next time. This is an example of the learning principle that a high fixed ratio of responses to reward leads to more responses.

Treatment for aggressive kicking is discussed in Aggression by Horses Toward Other Horses.

Pawing or digging in horses can be a result of frustration and anticipation. It could also be a displacement behavior. Treatment is like that for stall kicking.

Changing the floors to concrete might stop pawing behavior; however, it will not change the motivation for the behavior. Although most pawing is anticipatory, a horse might paw to reach a horse in the next stall. Standardbreds paw after exercise and might use the hole they create to redistribute their weight.

A head-shaking horse shakes or jerks its head uncontrollably, without any apparent stimulus. Some horses also snort, rub their heads on objects, and display an anxious expression. Most commonly, horses shake their heads up and down.

There are five grades of head shaking:

1. intermittent signs, mainly facial twitching

2. moderate signs, with noticeable shaking that can interfere with riding

3. advanced stage, and difficult to control

4. uncontrollable and unrideable

5. dangerous behavior with bizarre patterns

In most cases of head shaking, the horse looks as if it has nasal mites or is being attacked by biting flies. Many medical conditions can cause head shaking (eg, seizures, respiratory tract diseases and parasites, ear and eye disease, GI disorders, pain, trauma, nasal foreign bodies), and these must be excluded. The trigeminal nerve might be involved in some cases.

Behavioral causes of head shaking include an improper bit, an incompetent rider, fear and anxiety, extreme neck flexion during riding, and compulsive disorders. Geldings seem to be affected more frequently than stallions or mares.

Management of head shaking should include treating any underlying medical problem. A combination of cyproheptadine and carbamazepine has been helpful.

Some horses, almost always males, hurt themselves by biting their flanks or kicking the abdomen with their hindlegs. Some also vocalize.

Underlying causes include any type of abdominal discomfort, so a thorough medical examination is required. Skin diseases can also lead to self-mutilation and must be excluded.

Some geldings exhibit this behavior when pastured with mares. Management should include manipulating the social environment so that geldings are not housed with mares.

Trailer-related problems in horses are related to either loading into the trailer or traveling in the trailer. Horses can be afraid to load into a trailer because of innate factors (eg, neophobia, a dark interior, instability of the trailer, noise) and/or learned factors (eg, previous accident, motion sickness, previous punishment while loading).

A horse might load into a trailer readily but misbehave while inside. The reason for misbehaving inside the trailer might be that the horse finds it difficult to keep its balance while the trailer is moving, anticipates a stressful event such as a race after the trailer ride, or has motion sickness. In a small number of cases, horses are reluctant to leave the trailer.

Heart rate and salivary cortisol levels have been shown to increase during and after trailering.

The best approach to managing trailering problems is slow desensitization and counterconditioning using food. This approach might take a long time and might not be suitable for an acute problem. Desensitization should be undertaken long before the expected trailer ride.

Punishment for a trailer-related problem should be avoided, because it could aggravate the situation and be dangerous for both the horse and the caretaker. Positive reinforcement and clicker training have been used successfully to teach horses to load—even horses that previously refused to enter the trailer. Foals should be loaded with their mothers at an early age.

Sedatives such as xylazine can be used in acute situations. While drugged, however, the horse might not learn to load or ride better and might be less able to balance itself during the ride.

Behavioral anestrus (silent heat) is a common problem in young mares, especially during the first cycle. The ovaries are normal on palpation, and ovulation occurs normally, but the mare will not accept the stallion.

Causes of behavioral anestrus include environmental stressors and mating preference. Presenting several stallions might help, and if the mare is still nursing a foal, weaning or at least confining the foal out of sight of the mare might also be helpful.

Medical conditions that can cause excessive sexual behavior in mares include granulosa cell tumors and persistent ovarian follicles. These conditions should be differentiated because a persistent follicle might resolve without treatment (although it could require treatment with gonadotropins or luteinizing hormone or increasing daylight to ≥ 16 hours), whereas granulosa cell tumors require surgical removal.

Excessive estrous behavior is manifested as squatting and urinating frequently, receptivity to males, and exposing the clitoris (“winking”).

Some granulosa cell tumors produce testosterone, leading to stallion-like behavior (eg, aggression, mounting, flehmen, and urine marking). Many mares show estrous-like behavior when introduced to a new horse of either sex. They will squat and urinate but lash their tails rather than holding their tails to the side.

Overused stallions, submissive stallions presented to aggressive mares, and stallions with previous negative experiences might be unwilling to mate.

Masturbation is a normal behavior in horses; colts will start mounting within the first few weeks of their lives. Ejaculation is rare, and fertility rates are unaffected. Some owners use various devices to stop masturbation; these essentially punish the horse for masturbating, and they cause pain. They can cause fear while trying to breed and can predispose the stallion to poor libido.

Management of poor libido should be directed toward eliminating the underlying problem. The stallion should be presented with teaser mares, should be well rested and fed, and have increased social contact with mares on pasture.

Using an artificial vagina to desensitize the stallion can help, and treatment with anxiolytics such as diazepam can address underlying anxiety. Some cases might require semen collection and artificial insemination, if the stallion refuses to cover mares naturally.

Approximately 50% of geldings show some stallion-like behavior, including courting and mounting females, flehmen, fighting other males, and attacking foals. The brain of the male horse is masculinized before birth by the organizational effect of androgens; therefore, some of these behaviors will still be expressed in the absence of immediate androgen activation.

Some geldings can achieve erection and intromission while mounting a mare. Geldings that demonstrate consistent stallion-like behavior should be checked for a cryptorchid testicle. Normally, the blood testosterone concentration should be < 0.2 ng/mL.

Treatment includes separation, progestins, and cyproheptadine.

Coprophagia (eating feces) occurs mainly in foals during the first 8 weeks of life and is a normal behavior. Foals usually consume fresh feces of their mothers, and it is believed that maternal pheromones play a role in this behavior.

Deoxycholic acid is found in feces and might help protect against enteritis and aid in deposition of myelin in foals. Coprophagia might also provide vitamin B and introduce normal intestinal flora.

In adults, coprophagia is mainly associated with a low-roughage diet.

Decreased exercise and overfeeding a palatable and highly concentrated diet can lead to obesity. On pasture, horses spend 8–12 hours grazing while moving from place to place; confined horses spend < 3–4 hours feeding.

Increasing exercise, social contact, and roughage, and, if necessary, muzzling can help maintain appropriate body weight.

Horses are herd animals, and any changes in social relationships or the environment can increase stress and lead to decreased feed consumption. The presence of another horse can increase food intake through social facilitation or decrease food intake by causing fear if the other horse is dominant. Submissive horses might not eat near aggressive horses if they have previously been attacked.

Management should be directed toward the underlying problem. Increasing visual contact but preventing physical contact between horses can help.