Fish Oil Affects Glucose Clearance in Horses on High-Fat Diets

Fats and oils are good sources of energy for horses, but there is a link in some species between high-fat diets and insulin resistance. Long-chain omega-3 fatty acid supplementation (DHA and EPA) prevented the development of insulin resistance and improved insulin sensitivity in some species, and previous work in horses indicated fish oil (as a source of DHA and EPA) supplementation moderated glucose response to a grain meal, but did not affect insulin sensitivity. The aim of this study was to investigate the glucose dynamics in horses fed a high-fat or moderate-carbohydrate diet and to investigate if fish oil moderated these effects.

Four aged, nonobese Thoroughbred geldings were used in a study performed at Kentucky Equine Research. The treatments consisted of 1.5% body weight grass hay and 120 g/d vitamin/mineral supplement and either oats and corn oil; oats and fish oil; hay cubes and soy oil and corn oil; or hay cubes and soy oil and fish oil. At the end of each four-week treatment period, a frequently sampled intravenous glucose tolerance test was performed for three hours. At 20 minutes post glucose infusion, insulin was administered. Plasma samples were tested for triglycerides, insulin, and glucose.

Horses fed a high-fat diet (hay cubes and oil) had decreased glucose clearance compared with horses fed a moderate-carbohydrate diet (oats and oil). Fish oil significantly affected glucose clearance in the high-fat diet but had no effect on glucose clearance in the moderate-carbohydrate diet. Glucose clearance in the hay cubes/fish oil diet was not significantly different from either of the oat diets. Results of this study suggest that supplementing with fish oil can improve glucose clearance in horses fed a high-fat diet.