Effect of Adding Soybean Oil to a Horse’s Ration

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When fat is substituted for carbohydrate isocalorically (calorie for calorie) in a horse’s ration, blood glucose and insulin responses to feeding are reduced. It was unclear, however, whether this response was simply due to reduced glucose in the diet or if fat affects glycemic response in some other manner. An experiment carried out at Kentucky Equine Research (KER) was designed to evaluate whether adding fat to a grain meal would affect glucose and insulin response to feeding when the level of grain intake remained the same.

Nine Thoroughbred horses were used in this two-period switchback design experiment. Five of the horses were in training and were physically fit, and four were untrained. During period one, each horse was fed 2.27 kg (5 lb) 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 (6 lb) 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 post feeding. Water was available to the horses at all times. 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 the first period.

Blood samples were collected and analyzed for lactate, glucose, and insulin at the conclusion of the study. Blood glucose was significantly lower one hour after feeding when soybean oil was added to the diet. Glucose remained lower for 3 hours post feeding. After 6 and 10 hours, blood glucose was higher in the fat-supplemented group. Insulin was lower in the fat-supplemented group 1 hour after feeding. After 8 and 10 hours, insulin was higher in the fat-supplemented group. Plasma L-lactate tended to be higher in the control group 4 hours after feeding and higher in the fat-supplemented group 6 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 article was based on information in a paper titled “Responses of Blood Glucose, Lactate and Insulin in Horses Fed Equal Amounts of Grain With or Without Added Soybean Meal” by J. Pagan, T. Rotmensen, and S. Jackson. The complete paper can be found in Advances in Equine Nutrition, Joe Pagan, PhD, editor.