Does Feeding Affect Behavior?

Next time you visit your local feed and tack store, peruse the horse supplement section. Chances are you will find at least one that claims to have a "calming" effect on horses. Whether or not these supplements live up to these claims is debatable, but what is clear is that behavioral problems are of prime concern to owners, and they are more than willing to try supplements or treatments that might help calm their stressed, nervous, or excitable horses.

Then there's the issue of diet affecting a horse's behavior. Assertions regarding the effects of diet on behavior are commonplace in the equine community: "My horse is on a sugar high," or he is "heated up by too much grain or protein," and of course the "calming effect" of dietary fat. Is there any truth to these claims? We are all aware that various myths and fallacies surround horse feeding, and the area of nutrition affecting behavior is no exception.

There has been little research in this area and more studies are sorely needed. In the meantime, based on current knowledge, this article attempts to sort out fact from fiction concerning the effects of diet and feeding management on behavior. This issue must be examined from two viewpoints--both the effects of feeding management on behavior and the effects of specific feed types or ingredients.

Normal Feeding Behavior

Behavioral science is a vast and complex area, and a complete discussion of normal and abnormal horse behavior is well beyond the scope of this article. However, as an owner or trainer, it is important to have some understanding of a horse's behavior (particularly as it relates to feeding) in its natural environment and how confinement and modern feeding practices can lead to "unnatural" behaviors. These might include the nuisance repetitive behaviors (termed stereotypies or stable vices) such as weaving, cribbing, "wind-sucking," and wood chewing, as well as more subtle changes in temperament signifying nervousness, stress, or excitability.

The diet and feeding behavior of the intensively managed horse (i.e., kept in a stable or similar small, enclosed area) is clearly far removed from that of a horse in a natural environment (i.e., wide open pasture). When given free access to pasture, a horse will graze for 16 hours or more per day. His small stomach and large hindgut dedicated to the fermentation of fibrous feedstuffs are well adapted for this "trickle feeding" (small amounts, often). "Free ranging" equids will also roam great distances, exploring their environment and giving themselves ample natural exercise.

Contrast this natural grazing environment with the diet and day-to-day care of a horse kept in a barn or similar intensive management system. First, mostly for reasons of convenience, many of these horses receive only one or two meals per day. These meals are often devoured in short order, leaving a lot of down time in between meals and other daily activities. This drastic reduction in feeding time is the first possible link between diet and behavioral problems.

The second possible link relates to the makeup of the diet. To meet the energy demands for modern-day athletic activity, we feed our horses energy-dense concentrate feeds and, compared to a horse "on the range," intake of forages and other fibrous foods is greatly reduced. As we'll discuss shortly, both of these factors can contribute to development of certain behavioral problems.

Also bear in mind that the reduction in physical activity and normal socialization that goes with confinement housing could contribute to abnormal behavior. In the wild, horses love to explore their environment and would not put themselves in a small, confined area from which they could not escape predators. The frustration associated with a lack of physical activity or socialization with herd mates can result in problems such as stall walking and weaving or just pent-up energy that makes the horse difficult to handle when taken out of his stall.

Reduced Feeding Time and Fiber Intake

The reduction in feeding activity associated with meal feeding and a low-forage diet has been linked to development of some of the stereotypies. Instead of grazing upwards of 16 hours per day, a horse might spend as little as one hour per day engaged in feeding activity. Cribbing, chewing on wood, eating bedding (and even coprophagy, or consuming his own manure) might develop as a means to satisfy the horse's motivation for feeding activity.

The other factors at play are: 1) the low amount of forage consumed in a day; and 2) the concurrent high-level concentrate feeding.

The low forage/fiber intake (and amount of time during which the horse is occupied with feeding activity) results in a lot of "down time," particularly for horses kept indoors for much of the day. Researchers in Britain (McGreevy et al. 1995) and elsewhere have shown a higher prevalence of stereotypies when horses are fed a low forage/fiber ration (less than 15 pounds per day for an 1,100-1,200-pound or a 495-550-kg horse), and there is some evidence that providing a high-fiber diet can help in the management of established stereotypies.

The other part of the picture is the quantity of grain concentrate in the diet and its impact on gut acidity. In one study, a higher frequency of stereotypic behaviors was observed in horses on a high-grain diet (a 3:1 concentrate to hay ratio by weight) compared to a diet of hay alone. The incidence of these problems was diminished when a hindgut buffer, which helps to limit acidity in the cecum and colon, was included in the diet. One theory is that low-grade pain associated with gut acidity is a stimulus for development of stereotypies. By limiting gut acidity, it might be possible to reduce the incidence of these problems. Onset of cribbing in foals has also been associated with grain concentrate feeding. Researchers have proposed that cribbing might increase the flow of saliva, which in turn helps buffer acidity within the stomach and control gastrointestinal discomfort. Even if the diet is modified to reduce acidity, however, any stereotypic behaviors such as cribbing are often there to stay.

The take-home message is that wherever possible, we need to allow the horse to practice his normal feeding behavior. If pasture turnout is available, use it as frequently as possible. If not, the quantity and timing of forage and fiber feeding is critical. Aim to provide hay at about 1.5% of body weight (16-17 pounds per day for an 1,100-pound horse or 7.2-7.7 kg per day for a 495-kg horse) and divide that allotment into at least three feedings per day. The goal is to occupy more of the horse's time with feeding activity. The current trend toward greater use of other fiber sources, such as beet pulp, also can help.

Heated Up on Grain?

A common belief among horse owners is that corn or oats are "heating feeds"--that they give a horse too much "energy" and make him more excitable or difficult to handle. Who hasn't heard the term "feeling his oats" in reference to the perceived stimulatory effect of grain feeding on a horse's excitement level? Some also believe that there is a difference between corn and oats, corn being more of a problem because of its higher starch content. Rolled into this controversy is the issue of molasses, which some people say is bad for horses because it results in a "sugar high."

Note that we are using "energy" in the behavioral sense, meaning that the horse is mentally "hot" or "hyper," rather than in the nutritional sense, meaning the number of calories in a feed. However, feeding in excess of calorie needs (regardless of the source of those calories) can be one explanation for the "hyper" or "hot" horse, particularly when that horse spends much of the day in confinement.

This is a key point--before you reach for some magic "calming" potion as a solution for your hot-headed horse, take a good look at his overall diet and realistically assess his calorie needs. Some adjustment in feeding or activity level (or both) might make all the difference.

Nevertheless, there is evidence that, in some horses, the amount of dietary starch influences behavior. Based on fairly subjective assessments, researchers have reported that a decrease in the amount of dietary starch is associated with a decrease in the level of excitability.

Changes in brain chemistry might be the link between dietary starch and sugar intake and behavior. Serotonin, a brain neurotransmitter, is known to modulate mood, alertness, and activity. Indeed, low brain serotonin underlies several depressive disorders in humans, and some anti-depressant drugs work by enhancing serotonin's action in the brain.

More contentious is the effect of high serotonin. It is known that a meal that is high in glucose (a product of starch digestion) increases brain serotonin levels, and it has been proposed that this increase is responsible for the "sugar high" observed in some hyperactive children. In a similar manner, it is possible that big fluctuations in blood glucose after a grain meal could alter the behavior of horses through changes in brain serotonin activity.

However, before you take this information "to the bank," bear in mind that much more research is needed to sort out the specific behavioral effects of dietary starch and sugar in horses. There is also quite likely to be tremendous variation between horses, reflecting differences in genetics, environment, and the effects of other components of the diet. For the moment it is fair to say that some "hyper" horses (a good example being a young, high-strung Thoroughbred filly) can benefit from a reduction in dietary starch.

Fortunately, modern feeds for performance horses now include a variety of energy (calorie) sources--starch, fat, and highly digestible fiber such as beet pulp. The result is a significant decrease in starch and sugar compared to older-style feeds. Note that starch intake will be highest when straight grains are fed. Oats, barley, and corn are, respectively, 50%, 65%, and 70% starch. Even the new generation of "sweet feeds" have considerably lower starch compared to straight grains.

Fat and Protein

Fat has long been claimed to exert a calming effect in horses, and there is at least one research study (Holland et al. 1996) to support the contention that dietary fat reduces activity and reactivity of horses. As well, many owners and trainers have reported that their charges are more tractable when maintained on a fat-supplemented diet. A decrease in excitability and nervousness might be the reason that a higher-fat diet helps in the management of horses with some forms of chronic tying-up. Less clear is whether the "calming effect" of fat is actually due to the fat itself, or because when fat is added to the diet there is a substantial decrease in starch intake.

Like starch and sugar, in some quarters it is believed that dietary protein can make horses "high." Interestingly, studies in humans and dogs have shown that manipulation of specific amino acids in the diet can result in a change in aggression and hyperactivity. Whether the same is true in horses remains to be determined, but it might be that the type of protein (amino acid makeup) is more important than the absolute quantity of dietary protein.

Supplement Saviors

Not much is known regarding the potential benefits (and risks!) of supplements marketed as calming agents. There have been few scientific studies, and reported benefits are mostly anecdotal. These products often contain several ingredients, although the most common is thiamin, a B-vitamin. Because thiamin deficiency is known to cause problems with brain function (convulsions being the worst-case scenario), it has been rationalized that megadoses of thiamin might decrease anxiety and excitability in nervous horses. Thiamin supplementation is safe, and there might be other benefits such as appetite stimulation in picky eaters, but whether it has any effect in nervous and "hyper" horses is debatable.

More recently, supplementation with magnesium (one to two ounces of magnesium oxide per day) has been suggested as a treatment for nervous horses. Again, the rationale for this treatment stems from what is known about the effects of severe magnesium deficiency--general nervousness, excitability, muscle tremors, and convulsions. Bear in mind that magnesium deficiency is very rare in horses, and dietary intake is usually more than adequate. Nonetheless, it is easy to believe that supplementing horses with magnesium might help to calm horses. Like thiamin, some believe it helps, others don't.

What about herbal supplements? Nowadays, all sorts of herbal concoctions are touted for a variety of ailments, and some appear to have drug-like sedative effects. For example, in humans and mice, valerian (Valeriana officinalis) is an effective sedative. Alas, so far no data are available regarding herbal therapy for nervous horses. Worse, we have no idea whether these products are safe when consumed for weeks and months. The possibility of a positive drug test also looms when herbal supplements are used. More information regarding the safety and efficacy of herbal preparations is needed before I would recommended their use as calming agents.

The Bottom Line

Yes, horse behavior can be affected by diet and, in particular, feeding management. Although use of "calming supplements" might seem like the fastest and easiest solution to the excitable horse or one with undesirable behaviors, realistically a better approach is to critically examine the horse's overall diet and daily routines. Tweaking the amount fed, the quantities of starch, fat, and fiber in the diet, daily exercise, and the opportunity for socialization with other horses might make all the difference. 


Holland, J.L.; Kronfled, D.S.; Meacham, T.N. Behavior of horses is affected by soy lecithin and corn oil in the diet. Journal of Animal Science, 74, 1252-1255, 1996.

Johnson, K.G.; Rowe, J.B.; et al. Behavioral changes in stabled horses given non-therapeutic levels of virginiamycin. Equine Veterinary Journal, 30, 139-143, 1998.

McGreevy, P.D.; Cripps, P.J.; French, N.P.; et al. Management factors associated with stereotypic and redirected behavior in the Thoroughbred horse. Equine Veterinary Journal, 27, 86-91, 1995.

About the Author

Ray Geor, BVSc, PhD, Dipl. ACVIM

Ray Geor, BVSc, PhD, Dipl. ACVIM, is professor and chairperson of Large Animal Clinical Sciences at the College of Veterinary Medicine at Michigan State University

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