Efficacy of a fat-supplemented diet to maintain muscle glycogen stores and reduce thermal stress in exercising Thoroughbred horses

Abstract

Trial I. Twelve mature Thoroughbred horses were used to evaluate the efficacy of a fat-supplemented diet to maintain muscle glycogen stores and reduce thermal stress in exercising horses. In this study, exercising Thoroughbred horses were maintained in three body conditions (moderately low--condition score 4, moderate--condition score 5, and moderately high--condition score 6) and fed experimental diets containing similar nutrient-to-calorie ratios. The diets were (1) control (no added fat) and (2) 10% added fat. The horses performed standard exercise tests during which muscle biopsies were obtained from the biceps femoris. The muscle biopsies were utilized to determine muscle glycogen concentrations. Pre-test muscle glycogen concentrations were similar (P >.05) for horses in ML, M and MH condition groups. When the horses were fed the fat-supplemented diet, the comparable pre-test muscle glycogen concentrations were higher (P <.05) averaging 21.07, 26.06 and 24.42 mg/g, which was a 30%, 55% and 31%, increase, respectively, in resting muscle glycogen concentrations. Post-test muscle glycogen concentrations were similar (P >.05) for horses on all treatments. Trial II. Eight of the original Thoroughbreds, four males and four females were randomly divided into two groups of four with equal number of males and females. Following a pre-trial adjustment period, four horses from each treatment group were fed a control diet and the other four horses were fed a fat-supplemented diet. After the experimental period, a SET and energy balance trial was conducted. Upon completion of the energy balance trial, the horses were switched to the other diet. Again, a SET and energy balance trial were conducted. While consuming the fat-supplemented concentrate, horses had significantly lower (P <.01) total heat production. This reduction in total heat production resulted in a significant increase (P <.05) in available net energy for work for horses consuming the fat-supplemented concentrate. The heat increment of the fat-supplemented concentrate was significantly lower (P <.01) than the heat increment associated with the control diet. Thus, a significantly greater (P <.05) percentage of the net energy available in the horses consuming the fat-supplemented concentrate was available for work.