Glucose infusion increases maximal duration of prolonged treadmill exercise in Standardbred horses

Abstract

SummaryThe main purpose of this study was to describe the effect of glucose infusion on selected physiological variables and on the duration of treadmill exercise to fatigue. Six, 3–4 year old, clinically normal, Standardbred fillies were used in a randomised and balanced crossover design. The treatments were either an infusion of glucose (an initial bolus followed by an infusion rate adjusted during exercise to maintain glucose at approximately 9.0 mmol/l) or an infusion of a similar volume of normal saline. Saline was also infused during the first 30 min of recovery in both treatments. Treadmill speed and grade were 6.0 m/s and 2°. All horses underwent an exercise and dietary control period for 3 days prior to each treatment. A period of 7–10 days separated the treatments. Treadmill exercise duration was prolonged with glucose (89.8 min ± 15.4 s.e.m.) compared to saline (78.7 ± 12.4 min) (P<0.05). Plasma glucose concentrations were similar at rest and increased (P<0.05) above resting concentrations throughout exercise beginning at 15 min and 35 min for the glucose and saline trials, respectively. By 15 min of exercise, glucose concentrations were 8.72 ± 0.22 and 5.78 ± 0.28 mmol/l (P<0.05) for the glucose and the saline trials, respectively. Changes in haematocrit, plasma lactate, plasma total solids, plasma electrolytes, heart rate, core temperature, body weight and body water loss were similar for both treatments. An explanation for the glucose‐induced prolongation of exercise could be the availability of additional substrate during exercise.