The nutrition experts at Kentucky Equine Research give us some great information on fat in equine diets in the following article.
A number of studies have shown that when fat is substituted for carbohydrate in equine diets with the same caloric level, blood glucose and insulin responses to feeding are reduced. These studies, however, haven't shown if this response is due simply to reduced glucose in the diet or if fat affects glycemic response. Therefore, this experiment was designed to evaluate whether adding fat to a grain meal would affect glucose and insulin responses to feeding when the level of grain intake remained the same.
Nine horses were used in a two-period switch-back design experiment. Five of the horses were in training and were physically fit and four horses were untrained. During period one, each horse was fed 2.27 kg of a grain mix, which consisted of 72% oats, 20% corn, and 8% molasses at 7:00 a.m. Five of the horses were also fed 200 ml (170 g) of soybean oil mixed into the grain. At 8:00 a.m. each horse was given 2.72 kg of mature bluegrass hay. Blood samples were taken from each horse by jugular catheter before feeding, and at 1, 2, 3, 4, 6, 8, 10, and 12 hours after feeding. Water was available to the horses at all times. Blood plasma was analyzed for glucose, insulin, and L-lactate. The same procedure was followed two weeks later with the soybean oil added to the grain of the four horses that served as controls during period one.
Blood glucose was significantly lower one hour after feeding when soybean oil was added to the diet. Glucose remained lower for three hours post-feeding. After six and 10 hours, blood glucose was higher in the fat-supplemented group. Insulin was lower in the fat-supplemented group one hour after feeding. After eight and 10 hours, insulin was higher in the fat-supplemented group. Plasma L-lactate tended to be higher in the control group four hours after feeding and higher in the fat-supplemented group six hours after feeding.
These data suggest that the addition of fat (soybean oil) to a grain meal will affect glucose and insulin response to feeding. These effects are independent of the amount of carbohydrate in the diet and may be due to differences in the rate of gastric emptying when fat is included in the diet.
This report of KER's 1995 research was published in Proceedings of the 14th Equine Nutrition and Physiology Society Symposium. Reads the entire research paper, titled Responses of Blood Glucose, Lactate and Insulin in Horses Fed Equal Amounts of Grain With or Without Added Soybean Oil.