How Do Dietary Fat and Starch Affect Tying-Up in Horses?

Recurrent exertional rhabdomyolysis (RER) occurs in fit, nervous Thoroughbreds fed diets high in nonstructural carbohydrate (NSC). Clinical signs are diminished by feeding low-NSC, high-fat diets; however, the mechanism is unclear. This study was performed to determine if the glucose, insulin, and cortisol responses to isocaloric diets varying in fat and NSC availability differ in fit vs. unfit Thoroughbreds with RER.

Four fit RER Thoroughbred mares were exercised and fed 3 isocaloric diets in a 5-day/diet block design. Two high-NSC concentrated, sweet feed (SF) and a processed pelleted feed (PL) and a low-starch, high-fat feed (FAT) were used. After 24 h of rest and a 12 h fast, horses ate half their daily concentrate. Blood sampled for glucose, insulin, and cortisol was obtained before, immediately after, and at 30-60 minute intervals for 420 minutes. After a 3- to 6-month detraining period, the block design was repeated.

Results for SF and PL were similar. Regardless of diet, cortisol was higher in fit vs. unfit horses. Fit horses on SF/PL had higher post-prandial insulin and insulin:glucose ratios than unfit horses. FAT resulted in lower post-prandial glucose and insulin vs. SF/PL. Higher insulin in fit vs. unfit horses was not seen on the FAT diet. Increased postprandial glucose, insulin, and cortisol induced by high-NSC, but not high-fat, feeds are enhanced by fitness in RER horses. This combination may trigger rhabdomyolysis through increased excitability in RER Thoroughbreds.

This report of KER’s 2010 research was published in Equine Veterinary Journal.