Feeding status affects glucose metabolism in exercising horses

Four standardbred horses were used in a Latin square design experiment to evaluate the effects of feeding status on metabolic response to exercise. Horses were deprived of food overnight and then fed 0 (control condition), 1, 2 or 3 kg of corn grain approximately 2.5-3 h before exercise. The exercise test consisted of a warm-up phase (heart rate mean = 144 beats/min) followed by 800 m of walking and then a high intensity work bout for 1600 m (heart rate mean = 206 beats/min). All tests were conducted on a high speed equine treadmill on which the horses had been previously conditioned. During exercise, the control treatment resulted in steady plasma glucose concentrations, whereas all other treatments (1, 2 or 3 kg corn) caused a decline in plasma glucose. Liver glycogen concentration was decreased by exercise in the horses only when they received the control treatment. Plasma lactate concentration was increased by exercise but was not affected by feeding state. Plasma free fatty acid concentrations were highest when the horses received the control treatment. In addition, when horses received the control treatment, plasma free fatty acid concentrations decreased during the warm-up and high intensity phases of the test and increased during the walk phase. Free fatty acid concentrations changed in the horses receiving 1, 2 or 3 kg of corn grain only during the high intensity phase of the exercise test. Feeding status affects the metabolic response of horses to exercise thus further studies are necessary to evaluate the effect of feeding status on exercise performance.