Effects of Feeding on Behavior of HorsesBy Dr. Joe Pagan · May 25, 2012
There is certainly a great deal of controversy about whether the type of feed you give your horse affects its behavior. There are two schools of thought about whether feed affects behavior.
The more traditional way of thinking, and one held by many scientists, maintains that the only important factor governing feeding and behavior is caloric intake. If a horse is underfed and in negative energy balance, then it will not be as active or aggressive as when it is well nourished. Advocates of this point of view insist that when a horse’s behavior changes when it is on full feed, all the owner is really seeing is an expression of that individual’s “true colors.” They are more likely to suggest that the horse simply needs more training to become controllable when it is well fed. They would further insist that all you will get when you overfeed your horse grain is a fat horse.
A second school of thought acknowledges what so many horseman believe is indeed real. Certain types of feed may affect some behaviors in some horses. As of yet there is no concrete proof of this, but I would like to propose a mechanism of how feed might affect behavior. I must emphasize, however, that at this point this is only a theory and much more research is needed before it can be stated as fact.
When horses are fed a high-carbohydrate diet, they appeared to be more excitable and their heart rates were higher during an exercise test than when the same horses were fed a high-fat diet. In certain studies at the Kentucky Equine Research (KER) facility using objective measures of behavior, a difference was detected when horses were fed the same number of calories from different sources.
Why would grain affect behavior? When a grain meal is fed, blood glucose levels increase. The extent of increase depends on the type of diet and some horses have much higher blood glucose peaks than others. This much is fact.
Now it’s time for the theory. In humans, it has been suggested that many mental disorders such as schizophrenia, mania, and depression are the result of uncontrollable fluctuations of brain glucose levels acting in conjunction with insulin resistance. These fluctuations affect the production of the neurotransmitter serotonin. The behavioral disorder mania has been associated with hyperglycemia (high blood sugar) and hyperserotonergia (too much serotonin). Mania is defined as excitement of psychotic proportions manifested by mental and physical hyperactivity, disorganization of behavior, and elevation of mood. Does that sound like a horse you know?
Horses evolved eating diets that were fairly low in nonstructural carbohydrates (NSC), so in the wild they would not experience wide fluctuations in blood glucose and insulin. Insulin resistance is also common in certain horses, so it is conceivable that these horses may experience high levels of glucose and insulin in the brain. In rats, injection of insulin caused an increase in 5-HT (the major metabolite of serotonin). KER has conducted research demonstrating that supplemental trivalent chromium (from chromium yeast) increased the sensitivity of tissue to insulin so that less insulin was produced in response to a grain meal. Blood glucose was also lower, indicating that it was more efficiently cleared from the blood. Interestingly, there have been numerous reports from the field that horses given supplemental chromium appeared calmer and experienced a lower incidence of tying-up. Since nervousness is associated with many cases of tying-up, it is intriguing to speculate if these two problems (nervousness and tying-up) are related to insulin resistance in certain horses.
Again, it should be emphasized that the connection between behavior and feeding is only a theory, but if we assume that it is true, then what should we feed to reduce the high peaks in blood glucose seen in certain horses? Some guidelines include:
▪ Keep meal sizes small. Blood glucose increases in response to the size of the meal.
▪ Feed plenty of forage. Feed at least 1% of body weight to all horses and increase that to at least 1.5% in horses that are particularly excitable. If nothing else, they will spend more time eating and less time being bored.
▪ Add fat to the diet. Substituting fat for carbohydrates will reduce glycemic response. Fat contains about three times as much digestible energy (DE) as oats and 2.5 times as much DE as corn. Also, research at KER has shown that adding fat will actually reduce glycemic response of the NSC fraction of the diet, possibly by slowing gastric emptying.
▪ Substitute fermentable fiber for NSC. Certain fiber sources (beet pulp, soy hulls) can replace part of the grain in a horse’s concentrate.