Normal Behavior
Most domestic horses readily adapt to a variety of housing environments. That is, either immediately or within a few days they appear comfortable, reasonably content, and they adopt a pattern of maintenance behavior similar in many respects to that of horses at liberty. Basic maintenance behaviors include eating, resting, eliminating, grooming, and drinking. Table 1 lists quantitative guidelines for behavior patterns considered normal for mares in box or tie-stalls with other mares in the barn. This particular set of values is based on 24-hour videotaped samples of mares in box and tie-stalls in a variety of settings in North America. The pattern of behavior of mares in paddocks or at pasture, or even in natural social groups at liberty, would in most cases be quite similar. These values would be similar for stabled mature geldings, and would vary in the direction of generally higher activity level for young horses, for mares during estrus, and for stallions. Aged horses tend to be less active; they may rest for longer periods, take longer to eat, and so may have fewer major activity changes per 24-hour day. Horses typically have a daily pattern of behavior consistent with the management practices for each particular stable. For example, with hay provided 2-3 times daily in consumable portions, most eating of hay occurs immediately following feeding. With hay provided continuously, but freshened 2-3 times per day, freshening is typically followed by a lengthy bout of eating hay. It is interesting that almost all drinks are taken during or soon after hay or grain eating episodes.
Table 1. Behavior Norms for Mature Horse Mares in Box or Tie-Stalls
* hay fed 2-3 times daily or with hay available continuously
A somewhat surprising observation even for knowledgeable horse owners and veterinarians is that most stabled horses typically move about as much and at the same pace as horses in paddocks or at pasture (McDonnell, unpublished observations.) Even for horses in tie-stalls, the forward and backward steps while eating hay, responding to environmental stimuli, and interacting socially with neighbors is very similar to the number of steps taken in the same period of time by a horse in a spacious box stall, in a paddock, or in a herd at pasture.
Horses are very social animals, and to the extent possible they interact socially with stable mates. This includes attention and response to the actions of neighbors. It includes auditory, visual, olfactory, and tactile communication to the extent possible. It is usual for most horses in the barn to follow a similar daily pattern of behavior, as well as to perform particular behaviors simultaneously. That is, when one horse lies down to rest or gets up again to resume eating hay, typically neighbors will be doing the same. This is sometimes simply the result of most horses responding simultaneously and independently to an environmental event which evokes the behavior. It may also be the results of entrainment to the management routine. But in many cases it appears to include true social facilitation--one animal's behavior appears to elicit the same behavior in neighbors. This is very similar to what is seen in herds of horses at pasture.
Normal behavior of stabled horses also includes dominant or submissive behavior toward stable mates, even though they may never have direct physical contact. Among horses turned out together, the social order that establishes at pasture typically remains in effect in the stable.
In addition to a normal pattern of maintenance behavior, normal behavior of stabled horses includes appropriate responsiveness to environmental stimuli. In other words, the stabled horse is normally interested and reactive to events such as feeding, lights on or off, movement of people or animals, and disturbances in the barn. They tend to acclimate to a wide range of routine noises and activities, but continue to be disturbed by novel or abrupt events. The stabled horse also exhibits normal anticipatory behavior associated with feeding, cleaning of stalls, and such. So the behavior of the horses in a barn often reflect the degree of animal and human traffic interrupting their ongoing behavior. Also, as with general behavior patterns, there is a broad range of responsiveness that is considered to be normal, reflecting the broad range of temperament and experience among individual horses.
Among horse owners and managers, like parents, there are probably two schools of thought concerning routine. One school holds that the happy individual is one with a rigid routine that is set and kept. The other school holds that the happy individual is one that can deal with variety and flexibility in scheduling. Thoughtful behaviorists will tell you that the animal, child, or whatever organism can appear "happy" with either plan, but that the greatest risk of behavior problems is when the routine-bound organism experiences a breach of routine. Most horses readily learn to trust reasonable flexibility in a schedule of care and feeding, and in most instances probably enjoy a better human-animal interaction as a result.
Abnormal Behavior
When behaviorists catalog all the odd, abnormal, or unusual behaviors ever observed in stabled domestic horses, the list seems very long. But in reality the majority of abnormal behavior of stabled horses fit into a few distinct categories; the remainder are quite rare curiosities.
Behavior Indicating Physical Pain or Disease
Unusual behavior or a change in behavior is often the first sign of physical pain or disease. The astute caretaker of horses and the veterinarian depend heavily on behavior in assessing equine health. Change in appetite, prolonged or seemingly unprovoked anxious or agitated states, and non-physiologic postures or movements (e.g., leaning the body or pressing the head against walls, sawhorse stance, cocked head, shifting weight on limbs, looking/kicking toward abdomen, lifting/ringing tail) are all examples of behaviors that likely indicate physical root causes. It is beyond the scope of this presentation to describe all of the behavioral signs of physical pain and disease. Most good horsemen's veterinary guide books can orient the novice caretaker to the classic behavioral signs of physical discomfort and disease.
The Most Common Problem Behavior: Stereotypies
Stereotypies are repetitive, highly stylized, seemingly functionless motor responses and sequences. They occur in all captive wild and domestic species. In humans, stereotypies occur in normal as well as psychopathological states. They are a key component of autism, Tourette's, Lesh Nyan Syndrome, and obsessive-compulsive disorder. The classic equine stereotypies are listed in Table 2. In addition to the classic stereotypies, horses can develop a wide variety of stereotypical movements. Stereotypies are sometimes included in the category of misbehaviors called "stable vices," which also includes other annoying habits such as wood-chewing, water-tipping, blanket pulling, or refusal to be caught. The term stable vices has fallen out of favor, particularly for stereotypies, because of the connotation of intent.
Estimates of the prevalence of stereotypies among domestic horses have ranged considerably, from as low as 1% to as high as 26%. Considerable variation among subpopulations of domestic horses is well recognized. In captive wild equids, the incidence of stereotypies is much higher (greater than 40% of animals). The severity of stereotypy varies considerably among animals and within an individual over time. The level of confinement per se is not as important in stereotypies as is traditionally assumed. Social isolation or separation is often a more important factor. For example, horses in tie-stalls with close contact with neighbors typically have very low incidence of stereotypies. Another interesting observation is that for horses with severe locomotor stereotypies (weaving, pacing, self-mutilation) in box stalls or at pasture, movement to tie-stall housing with or without neighbors often eliminates the stereotypy (McDonnell, unpublished clinical observation).
It is not clear whether stereotypies should be viewed as abnormal behavior, misbehavior, or whether they represent a normal "coping" behavior which reduces stress. There also remains considerable controversy about the factors involved in stereotypies in horses as well as in other species. Management conditions (housing, social, exercise, nutrition) and genetic predisposition are considered important factors. The view that all stereotypies are abnormal and the result of boredom or frustration of stable life is now known to be too narrow. Certainly there can be medical causes, yet for a large percentage of the cases one cannot be identified. In many of these the behavior may appear genuine, as opposed to a simple attention getting or "boredom" activity. In some individuals, no matter what the root cause, the stereotypy clearly appears exacerbated by social, nutrition, and exercise factors.
Table 2. Equine Stereotypies
Several laboratories have confirmed that endogenous opiates rise during the performance of a stereotypy in horses. In horses that perform a stereotypy in the absence of an obvious physical, medical, or apparent environmental cause, the assumption is made that the behavior likely initially had a tangible cause, but has now become a habit maintained by the reward of opiate release.
The trend in clinical veterinary behavior has been to call stereotypies ''obsessive-compulsive disorder." One reason is that these behaviors in animals often respond well to treatment with drugs that are also effective for relieving the behaviors associated with obsessive-compulsive disorder in people. This label implies a much more complex cognitive component to stereotypies than we can assume is the case with animals.
A consistent observation is that some horses appear much more likely to perform a stereotypy than others, and that the predisposition may run in families. Marsden and coworkers in Edinburgh1 recently surveyed the history of stereotypies among captive Przewalski horses for which breeding histories are well documented. They concluded that genetics is an identifiable factor.
Key traditional methods for treating stereotypies include physical and social environmental manipulation, nutritional changes, physical restraint, and aversive conditioning. These have been reviewed in detail elsewhere2. Pharmacologic aids which in some cases have appeared helpful include long-acting tranquilizers and serotonin enhancing agents (tricyclic anti-depressants, l- tryptophan).
Acupuncture and acupressure methods are under development for treatment of behavioral problems in horses. Auriculotherapy in the form of acupuncture, acupressure, or surgical stapling of the ears is now a popular treatment offered for cribbing. The results of this treatment alone are rarely long-lasting. The same procedures that are used to relieve estrus cycle and ovarian problems are used for stereotypies3.
Treatment of equine stereotypies is also becoming quite a controversial topic. If a stereotypy is a normal coping mechanism, should you try to eliminate it in any way other than eliminating the cause? So anti-cribbing surgery, aversive conditioning, physical restraint and pharmacologic treatments are being seriously questioned, particularly in some parts of the world. Systematic behavior evaluation including detailed study of 24-hour videotaped samples of the horse's behavior can usually provide considerable information about the possible causes and exacerbating factors that can lead to a individualized management and treatment program.
Some New Findings on Stereotypies
Light or sound induced headshaking.
Madigan and coworkers in California4 have found that some headshaking in horses appears to be induced by light or sounds. It is believed that certain horses are sensitive to bright light and sharp sound. These stimuli appear to hyperactivate the trigeminal nerve resulting in a nasal irritation. This is believed to be similar to the photic sneeze syndrome in humans. The light or sound-induced headshake is a more violent and irregular, snorting toss, compared to the more rhythmic traditional head bobbing or nodding seen as a classic stereotypy. The horse may appear to be trying to scratch its nose on a foreleg or even on the ground as it snorts, even going along at a trot or canter. This form of headshaking almost always worsens under work, and immediately subsides as the animal is returned to the quiet and dark barn or rest, so is easily misinterpreted as a purely behavioral problem. In most cases, light-induced headshaking is seasonal, and will stop immediately when the eyes are covered or the area is darkened. Dark goggles or sun-blocking face masks may be all that is needed for some individuals.
Cribbers don't swallow air.
McGreevy and coworkers in Bristol, England5, have used endoscopy and fluoroscopy to evaluate the process of cribbing. They concluded that cribbers don't actually swallow air to the stomach. Rather a bolus of air is formed in the esophagus and then expelled, with little or none passing caudally to the gastro-intestinal tract. The characteristic grunt of cribbing occurs as incoming air passes through the cricopharynx.
Other Common Problem Behaviors
There are several problem behaviors that are often lumped with stereotypies, but are clearly distinct. Examples include wood-chewing, digging, stall destruction, wall-climbing, playing with water, and general frenzied or aggressive behavior. These problem behaviors can usually be satisfactorily reduced or eliminated by evaluation of the precipitating or exacerbating conditions and creative management and/or formal behavior modification techniques.
References
1. D Marsden, personal communication, 1994.
2. Houpt KA and McDonnell SM(1993) Equine stereotypies. The Compendium 15 (9): 1265- 1272.
3. A M Sheen and J Schumacher, personal communication, 1996.
4. Madigan JE, Kortz G, Murphy C, and Rodger L (1995) Photic headshaking in the horse: 7 cases. Equine Veterinary Journal 27: 306-311.
5. McGreevy PD, Richardson JD, Nicol CJ, and Lane JG (1995) Radiographic and endoscopic study of performing and oral based stereotypy. Equine Veterinary Journal 27: 92-95.
About the Author
Dr. Sue M. McDonnell heads the Equine Behavior Laboratory at the University of Pennsylvania School of Veterinary Medicine, where her work includes clinical research, and teaching activities focused on horse behavior. She is internationally known for her research-based scientific approach to equine behavior. Dr. McDonnell maintains a semi-feral herd of ponies specifically for the study of their behavior under semi-natural conditions.
This information was presented at, and appears in the Proceedings of the 1998 Alberta Horse Breeders and Owners Conference.
Published at the Goverment of Alberta Agriculture and Rural Development website (Agri-News)