Pasture, Hay, and Horses: A Nutritionist's Perspective.

Forage is an essential part of equine feeding management, however few forages have been developed with the nutrition of the horse in mind. In the last 10 years horse owners have become increasingly interested in the effect of forages on the health and wellbeing of horses, particularly horses that are at risk for certain metabolic or digestive disorders. The equine digestive tract is much different from that of a ruminant, and consequently, the digestion, absorption and metabolism of compounds in forages is also different. In the horse, minimal digestion occurs in the stomach. After passing through the stomach, enzymatic digestion in small intestine results in the absorption of simple sugars, available amino acids, vitamins and some minerals. The availability of amino acids for small intestinal absorption is important for horses with high amino acid needs such as broodmares and growing horses. On the other hand, forages that are high in simple sugars can elevate blood glucose and insulin levels which may be undesirable for horses with certain metabolic diseases. Any material that escapes digestion in the small intestine passes to the large intestine (cecum and colon) where it can be acted on the by the resident microbial community.  In general the neutral detergent fiber fraction of forages is slowly fermented in large intestine to mainly acetate, with smaller quantities of propionate and butyrate production. However, other carbohydrates that reach the large intestine, such as fructan, can be rapidly fermented which can affect the profile of volatile fatty acids, reduce pH and possibly disrupt the microbial community. Because of the differences in digestive processes in horses and ruminants, forages that have been selected to increase performance of cattle and sheep may not be as desirable for horses.