Nutrition and Equine Behavior

In trying to figure out what makes horses tick, or in this case, behave badly, here’s a look at the studies on diet and its effect on animals.

All of us would like calm level-headed horses instead of “ill tempered” horses that are frustrating and potentially dangerous. While different approaches have been taken to moderate behavior, such as the explosion of resistance-free trainers that help us deal with difficult horses by teaching us to think like a horse, we are still searching for the cause of bad behavior and nutrition is high on the list of possibilities.

First and foremost, we must remember that horses are herd animals with inherent flight instincts and they respond to us like any other herd animal—when they perceive danger, they usually want to run. The next critical factor in equine behavior is environment. Are they allowed enough free-choice exercise? Can they see and interact with other herd mates? Have they been mistreated in the past?

Outside of instinct and environment, more people are blaming diet for poor equine behavior. While there are numerous human research studies into the role of nutrition in behavior, very little research has been conducted on the role of nutrition in horses. Despite the lack of evidence, I firmly believe that diet can potentially affect any cell in the body. Be warned, however, nutrition is not a quick fix for poor behavior, but rather a useful tool with some horses.


Most nutritionists discount the common belief that a high-protein feed will make horses nervous. But, let’s look at the facts. When feeding a higher-protein feed, we are also feeding a diet rich in carbohydrates that might make the problem excess protein or carbohydrates. With most grain meals, the horse will experience a large increase in blood sugar and then a release of insulin, which has been proven to influence the activity of the brain’s neurotransmitters, specifically dopamine and norepinephrine. (Neuro­transmitters are amino acid-based hormones that allow one brain cell to communicate with a neighboring nerve cell.)

Another potential means by which high-protein diets can influence behavior is the amino acid tryptophan. Tryptophan is the precursor to the important neurotransmitter serotonin so, in theory, dietary changes of tryptophan could influence behavior through changes in serotonin levels (a regulator of emotions and judgment).

A recent study in aggressive dominant dogs suggests that a low-protein diet is beneficial because it allows higher amounts of tryptophan to pass the blood-brain barrier allowing more serotonin production. With high-protein diets, other large neutral amino acids compete with tryptophan for entry into brain chemistry. Caution must be exercised in extrapolating a conclusion from carnivorous canines to our herbivore horses. However, the research on dogs could be a logical explanation for why high-protein diets might influence equine behavior. As a supplement, tryptophan has been given to horses with no significant conclusions. When given to dogs, in the form of Griffonia seed extracts, tryptophan proved toxic, leading to excess serotonin production.

“Horses fed the higher fat walked less in their stalls and were significantly less reactive to various stimuli such as can rattling and umbrella opening.”

Other reasons for protein’s possible role in behavior are blood ammonia and urea. We know that excess protein is converted to ammonia by the bacteria living in the horses’ hindgut. And we know that because ammonia is toxic, it must be converted to urea in the liver and eventually excreted through the kidneys. Could pH changes in the horses’ hindgut alter nutrient status and affect behavior? Could blood ammonia and urea levels from higher protein diets alter brain chemistry? Could a horse fed a high-protein diet have a temporally altered hydration status significant enough to alter brain chemistry? One theory in attention deficit disorders in children is based on foods or food extracts altering brain activity.

With all of this in mind, I no longer discount a horseman’s statement that a high-protein diet alters their horses’ behavior. It may be through insulin, tryptophan, urea, hydration status or other unknown mechanisms, but until qualified equine studies are completed, I try not to overfeed protein. Remember most adult horses do not require more than 10 percent protein in the concentrate.


Another possible contributor to equine behavior is fat. Many equine researchers have proven numerous benefits of higher fat rations on athletic performance and body condition, but beyond that, many owners report a leveling of their horses’ behavior. Dr. Janet Holland and her group at Virginia Tech investigated this phenomenon by measuring spontaneous activity and reactive responses in horses fed a 10 percent fat ration. Horses fed this higher fat ration walked less in their stalls and were significantly less reactive to various stimuli such as can rattling and umbrella opening. With a high-fat diet, blood glucose and insulin will tend to remain more level but with lower blood glucose and insulin, some believe brain neural transmitters are negatively altered.

The reason for this might be found in ketones—a byproduct of fat metabolism. It is thought that ketones can pass the blood brain barrier and improve brain chemistry, as witnessed in some epileptic children who, while on a ketogenic diet (high fat), stopped having seizures.


Electrolytes are another area in nutrition that has been considered in equine behavior—specifically, magnesium supplements that claim to have a calming effect on horses. We do know that horses require magnesium. (I believe the current requirements of National Research Council are too low.) It may be that horses need higher magnesium today because of the competing effect of excessive potassium or calcium. For example, forages that are grown on fields with intense manure spreading are often very high in potassium. It has also been said that horses consuming calcium rich alfalfa need more magnesium. But, clearly, the influence of higher potassium and calcium on magnesium metabolism needs further study.


Chronic pain can also alter a horse’s personality. A new study of show horses with gastric ulcers listed a recent change in personality as a primary symptom. These researchers found about 50 percent of show horses on the road longer than 10 days per month had gastric ulcers. It would follow that many of these horses display a behavior problem because of chronic stomach pain.

Since this study, I have witnessed personality changes tied to diets aimed at preventing gastric ulcers. These diets are beet-pulp based with chopped alfalfa mixed into the concentrate. The theory with these diets is to feed horses free choice to encourage small frequent meals in order to buffer stomach acids, making ulcers less of a problem. These diets are also high in fat, so the witnessed improvement in behavior could be a result of fat or pain relief, or both. Again, more controlled clinical studies are needed.

All of the above nutrient interactions are interesting to consider. We do have hard evidence of the benefits of higher fat rations on behavior. We have evidence in other species on how protein and amino acids may be involved. It is also logical to consider electrolyte balance and chronic pain on behavior. However, I need to stress again the primary importance of genetics and environment. A young foal will learn behavior traits from their dam. Nutrition can play a role in behavior but the best medicine for many misbehaving horses is consistent exercise, which will do more for a horse’s disposition than any ration or supplement.






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