A variety of behavior problems occur in horses. Some of the most common are those associated with aggression (including aggression towards people), abnormal eating habits, and undesirable stall behaviors. see Behavior of Horses: Behavior Problems in Horses* 

The most common types of aggression towards people in horses are similar to dominance aggression and fear aggression in dogs. Fear can be caused by physical abuse, harsh treatment, and night blindness associated with confinement in a dark stall. Horses that are aggressive to people are sometimes too dangerous to keep. There have been cases of horses killing people in such circumstances.

Aggressive behavior can be modified using counterconditioning and desensitization (using rewards for nonaggressive reactions). Rewards could be frequent feedings of highly desirable foods (for example, molasses or apples), attention, grooming, or exercise. The purpose of the frequent feeding is to mimic the natural pattern of frequent grazing and to associate that with the person's presence. All aggressive animals should probably be neutered because aggression appears to be hereditary, and removal of sex hormones reduces some types of aggression.

Aggression towards other horses is usually associated with sex or may be secondary to fear. Horses have preferred grooming and grazing partners. The extent to which these preferences may be a factor in aggression to other horses is unknown. Treatment may include castration, desensitization, and counterconditioning see Behavior of Horses: Behavior Modification in Horses. This can be done gradually by introducing horses across 1 or 2 fences so that they do not injure each other. Two fences are best because they reduce the possibility that the horses could strike each other with their feet.

Wood chewing may be associated with the normal equine pattern of browsing. Under free-ranging circumstances, horses graze 12 to 14 hours per day. Most wood chewing occurs in the winter, and it appears to take place more often in horses that are fed pelleted diets. If a horse receives less than 1 kilogram of hay per 100 kilograms of body weight, wood chewing can become extreme. It is important to address the primary problem (that is, learn why the horse is doing it), rather than merely trying to prevent it. To treat this condition the owner should increase both roughage (hay, for example) and exercise through work or increased pasture time, because wood chewing is sometimes caused by boredom.

Coprophagia is the eating of feces and is a normal behavior in foals. It is most common in the first month of life, after which it usually declines. When it is seen in adults, it is usually associated with low roughage or protein in the diet or a dietary deficiency. Treatment includes increasing the amount of roughage and protein in the diet.

Pica is the consumption of soil or sand or other nonfood items. This can lead to serious and even fatal digestive complications, and therefore should not be taken lightly. By nature, horses spend much of their time grazing and if this activity is curtailed, such as when stabled, they are likely to seek other materials to consume. Lengthy periods of confinement, often combined with concentrated feeds that are quickly consumed, can cause boredom and lead to abnormal eating behaviors. Texture may be important, and the addition of roughage and salt blocks may have a role in treatment.

Horses form friendships with other horses, and anorexia (loss of appetite) can be associated with changes in these relationships. For example, if a horse is separated from a companion it may stop eating. Addressing the social aspects of the problem is important. Your veterinarian may also prescribe drugs that stimulate appetite. In foals, poor appetite may be due to an aggressive mare attacking a foal that tries to share the mother's food. Barriers should be erected that safely permit normal development and feeding patterns. Foals may not eat the same plant or same plant part as the mare, and the part they choose may be based on the height of the plant. This problem should be addressed and creep feeders should be placed near the mare so that the foal does not have to choose between food and contact with its dam. Foals on pasture that are nursing do not drink water, but the mares need access to good, clean water.

Obesity can be the result of decreased exercise, increased palatable food, and understimulation (horses that eat in the absence of other activities). Food should not be abruptly removed from an obese horse. The amounts of food should be decreased gradually while increasing exercise. The diet should also be evaluated for nutritional content and adjusted to make a more balanced ration. This will help the horse lose weight.

Stall walking or circling is usually in response to separation from another horse. It is usually rapid and accompanied by vocalization. Horse owners should watch for signs of anxiety (pacing or changes in vocalization when stable mates or housing conditions change). Treatment should include increasing exercise, providing social company, allowing the horse to see other horses, and providing clean bedding. Feeding frequently, providing more open stalls, and providing better access to outside views can also help. Adding toys to the stall may help if the horse is young and active.

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Behavior Problems in Horses*  Behavior Description Causes Aggression Biting Nipping during handling or when in close proximity Boredom; bad temperament Charging Attacks handlers or those in close proximity Bad temperament; meal time; overly protective of foals; hormone problems in mares Crowding Invades handler's personal space Nervousness; learned avoidance mechanism Kicking Lifting hind foot forward and then kicking back in a sideward motion towards an object (not to be confused by just kicking to get rid of flies on legs) Fear; bad temperament; aggressiveness (usually towards other horses) Rearing Striking with front legs while standing on hind legs Fear or objection to restraint, medication, or other stimuli; harsh bit; learned avoidance mechanism Striking Reaches for handler with either or both front feet Reflex to pain; fear; confinement; bad temperament Fear Halter pulling Pulls back when tied; panics when cross-tied; doesn't follow handler Poor training; learned avoidance mechanism; pain Evading haltering Runs away when approached; avoids being caught Fear or mistrust of people; anticipation of bad experience Performance problems Balking Resists moving forward Fear; failure to establish clear cues; asking horse to perform beyond its abilities Bucking Kicks up hind legs forcefully Playfulness; desire to unseat rider; frustration from unclear training cues; ill-fitting equipment  Head tossing Throws up head when grooming exercising, or riding Tooth infection or medical problem; painful bit pressure; learned avoidance mechanism Eating problems Coprophagia Eats manure Normal in foals 2 to 5 weeks old; lack of roughage, minerals or proteins Cribbing Bites an object, pulls back flexing neck Boredom; lack of exercise Food bolting Swallows food rapidly without chewing Excessive hunger; competition for food; learned behavior Mane and tail chewing Chewing on manes and tails of herdmates Boredom; playfulness; lack of roughage or minerals Wood chewing Chews on wood Lack of roughage, protein, or minerals; boredom Stall problems Digging or pawing Paws floor Anticipation of feed; nervousness; lack of exercise Tail rubbing Rubs tail against fences or walls Parasites; habit Stall walking; stall weaving; stall kicking Continuous circling, moving, kicking  Boredom; excess energy; aggression  *Adapted with permission from EB1657—Identifying Abnormal Equine Behavior and Vices, Washington State University Extension. Behavior Problems in Horses*  Behavior Description Causes Aggression Biting Nipping during handling or when in close proximity Boredom; bad temperament Charging Attacks handlers or those in close proximity Bad temperament; meal time; overly protective of foals; hormone problems in mares Crowding Invades handler's personal space Nervousness; learned avoidance mechanism Kicking Lifting hind foot forward and then kicking back in a sideward motion towards an object (not to be confused by just kicking to get rid of flies on legs) Fear; bad temperament; aggressiveness (usually towards other horses) Rearing Striking with front legs while standing on hind legs Fear or objection to restraint, medication, or other stimuli; harsh bit; learned avoidance mechanism Striking Reaches for handler with either or both front feet Reflex to pain; fear; confinement; bad temperament Fear Halter pulling Pulls back when tied; panics when cross-tied; doesn't follow handler Poor training; learned avoidance mechanism; pain Evading haltering Runs away when approached; avoids being caught Fear or mistrust of people; anticipation of bad experience Performance problems Balking Resists moving forward Fear; failure to establish clear cues; asking horse to perform beyond its abilities Bucking Kicks up hind legs forcefully Playfulness; desire to unseat rider; frustration from unclear training cues; ill-fitting equipment  Head tossing Throws up head when grooming exercising, or riding Tooth infection or medical problem; painful bit pressure; learned avoidance mechanism Eating problems Coprophagia Eats manure Normal in foals 2 to 5 weeks old; lack of roughage, minerals or proteins Cribbing Bites an object, pulls back flexing neck Boredom; lack of exercise Food bolting Swallows food rapidly without chewing Excessive hunger; competition for food; learned behavior Mane and tail chewing Chewing on manes and tails of herdmates Boredom; playfulness; lack of roughage or minerals Wood chewing Chews on wood Lack of roughage, protein, or minerals; boredom Stall problems Digging or pawing Paws floor Anticipation of feed; nervousness; lack of exercise Tail rubbing Rubs tail against fences or walls Parasites; habit Stall walking; stall weaving; stall kicking Continuous circling, moving, kicking  Boredom; excess energy; aggression  *Adapted with permission from EB1657—Identifying Abnormal Equine Behavior and Vices, Washington State University Extension.

Weaving occurs when a horse that normally stall walks is tied or prohibited from walking due to restricted space. Because they cannot circle as usual, they will still move constantly, but in a weaving motion. Treatment includes untying the horse, providing a larger stall, or best of all, turning the horse out onto pasture. The other treatments recommended for stall walking see Behavior of Horses: Behavior Problems in Horses can also help.

Pawing can cause injury to the horse, damage the floor, and cause wear to the horse's hooves. It is a normal behavior and can occur when horses on winter pasture are forced to dig for feed. When horses are confined and fed highly palatable foods, pawing can occur more frequently and more intensely than it would otherwise. The underlying cause of the pawing needs to be determined in order to successfully treat it. Specific treatments are similar to those for stall walking see Behavior of Horses: Behavior Problems in Horses. Pawing should not be rewarded, which is what inadvertently happens when horses paw in anticipation of feeding. The food should be presented to the horse only when the horse is not pawing, or the horse should be brought to the food.

Kicking damages horses' legs and stalls. It is often an aggressive behavior that appears when another horse is nearby or when the horse perceives that another horse is nearby. Kicking can also occur in anticipation of food. It may also occur when the horse cannot achieve its goals (for example, exercise or a chance to breed). For successful treatment, the underlying causes of kicking should be determined. Treatment is as for stall walking see Behavior of Horses: Behavior Problems in Horses. It may also require rearranging the social grouping in the barn.

Cribbing (windsucking, crib biting) is a distinct behavior, different from wood chewing, that involves grasping a horizontal surface with the front teeth (incisors) and flexing the neck without swallowing air. The activity produces strange, nonflatulant sounds. Cribbing is most easily diagnosed by noticing the missing U‑shaped pieces from the available fencing. Horses that crib have worn teeth and develop thick neck muscles. Treatment options include increasing roughage in the diet, changing companions, and providing greater access to pasture.

Self-mutilation may be due to a medical problem such as a digestive disorder or colic. The progression of the problem should help to differentiate a medical problem from one that is primarily behavioral. In horses, most self-mutilation involves biting of the limbs, chest, or flanks. Self-mutilation can appear in sexually frustrated (usually male) or socially incompatible horses. Treatment should include correction of the underlying problem. Self-mutilation associated with sexual frustration can be addressed by castration, pasturing with a mare, removing all mares, increasing exercise, increasing roughage, and decreasing grain.

Foal rejection is seen in 3 main forms: mares that will accept the foal but will not let it suckle, mares that are fearful of the foal and run away, and mares that exhibit stallion-like behavior and attempt to kick or bite the foal. Mares may paw at foals to stimulate them to rise from recumbency, which is different from rejection. Mares can kill their foals if they are underweight and not getting enough to eat, and this can be a normal, although uncommon behavior. The first step in treatment is to protect the foal. If the mare will accept the foal but not let it suckle, the mare should be helped through several nursings until she learns that suckling is pleasurable. Holding her in such a way that she cannot injure the foal may involve either cross-ties or partial barriers through which she can see and smell the foal but that prohibit her from reaching for it. The mare should be checked to make sure there is nothing wrong with her udder, such as mastitis or sores that could be causing her pain, which can explain an aversion to nursing. Pressure in the udder resulting from infrequent nursing can be treated using warm water baths and soaks, light massage using a hose, and milking the mare.

Mares that are afraid of their foals should be treated in the same manner, but the addition of relaxation cues such as darker, quieter stalls and food treats may help. Dogs have been used to evoke maternal “herding” behavior by stimulating the mare to protect the foal from a potential threat. Mares that attempt to injure their foals must be restrained using stocks or bars. At the same time, the mare can be counterconditioned using positive rewards. If the mare cannot be retrained or trusted, a replacement (“nurse”) mare should be sought or other arrangements made (hand nursing) so that the foal can be adequately nourished.

Stallions have poor libido if they are overused for breeding, are inhibited because of the use of antimasturbation devices, are used out of season, or are injured while breeding. Masturbation is a normal equine behavior. There is no truth to the myth that masturbation depletes semen value because horses that masturbate rarely ejaculate. Stallions that have poor libido should be rested if they have been overused. Another cause of poor libido can be a poor breeding environment. Many stallions are “picky” about the environment in which they are collected and may exhibit signs of poor libido if the environment is not right. Distractions such as yelling, rapid and unexpected movement, and rough handling can lead to a stallion that has no interest in the situation at all.

Letting a stallion that exhibits poor libido watch other stallions mate may have a beneficial effect on their libido. Providing them with a variety of mares can also stimulate their interest. Pasturing with a mare may also help.

Stallions that are aggressive during breeding are often overused or used out of season. These stallions may benefit from the use of an artificial vagina out of season so that they learn that the experience is pleasurable. Stallions may develop mating preferences and may not be compatible with the chosen mare, so changing the mare may help. If stallions were stabled with mares when they were colts, they may have some social inhibition with mating, and forced mating can result in aggression. Successful treatment involves identifying the underlying problem.

Nymphomaniac mares “wink” (show the clitoris), squat, and urinate frequently, often when they are not in heat. Mating behaviors and those involved in solicitation are not considered abnormal if they occur every 21 days when the mare cycles. Nymphomaniac mares should be checked for underlying medical problems.

Geldings that act like stallions will mount mares, attack foals, fight with other males, and self-mutilate. These geldings may also disturb other social relationships. Laboratory tests may be helpful to exclude underlying medical problems, although about 10% of normally castrated stallions will retain stallion-like behavior.

Problems with trailering include refusing to enter or leave the trailer and scrambling. All of these can be potentially injurious to the horse and are best addressed early. Often, treatment can be as simple as backing the horse into the trailer (using a platform rather than a ramp), walking the horse slowly around and then into the trailer, using another horse that trailers well as a “buddy,” and counterconditioning and desensitizing by using treats. Trailers can be designed to allow bidirectional entry and exit and a walk-through option. Walking through the trailer may help demonstrate that the horse is not walking into a dark, uncertain area. Once the horse is calm, the gate can be raised.

Last full review/revision July 2011 by Karen L. Overall, MA, VMD, PhD, DACVB, ABS Certified Applied Animal Behaviorist