Have you ever wondered why some horses are tractable part of the time, but hard to control or "hot" other times? Or why some foals have skeletal problems when everything possible was done to provide nothing but the best feed and care? Or why some performance horses tie up (azoturia) periodically? While still controversial in the world of equine nutrition, studies reveal that a high-carbohydrate diet, which produces a high glycemic response (the level of blood glucose that rises in response to a meal), might be the culprit in some of these problems.

According to Joe Pagan, PhD, president of Kentucky Equine Research (KER) in Versailles, Ky., "There is growing evidence that when certain horses eat feeds that produce large amounts of blood glucose, it may affect the horses' behavior or health."

Pagan, who founded KER in 1988, emphasizes that glucose is necessary for the life function of a horse. But, he says, "Consider the diet of horses in the wild. They eat high-forage diets which contain very little sugar. When horses eat forage, the bacteria in the large intestines break down the plant cell walls and produce volatile fatty acids as a by-product of this fermentation. It is these volatile fatty acids that can be used to produce glucose. Horses make glucose from fiber fermentation, but it is a more steady production of glucose that does not cause large fluctuations in blood glucose. However, today's domestic horses, due to smaller pastures and higher athletic expectations, are often fed concentrated feeds, many of which are high in starch and sugars.

"It is not the glucose, per se, that causes some potential problems," he clarifies. "It is the resulting insulin. Glucose increases the production of insulin, which is an anabolic hormone that sends the glucose to the muscles and liver to be stored as glycogen, both of which are important fuels for performance horses