Effect of maltodextrin supplementation on blood glucose, lactate, insulin, and cortisol levels of horses subjected to submaximal incremental exercise test

Riders and trainers believe that oral maltodextrin (MD) supplementation prior to exercise increases blood glucose availability and delay the onset of fatigue in horses, although there is no evidence supporting this claim. Therefore, we aimed to evaluate the effect of MD supplementation on blood glucose, L-lactate, insulin, and cortisol levels and heart rate in horses subjected to an incremental exercise test. A randomized placebo-controlled crossover trial was designed to test the effect of three doses of MD (50 g, 100 g and 200 g) on blood glucose, L-lactate, insulin, and cortisol levels and heart rate of four Purebred Lusitanian geldings. A seven-step incremental field exercise test was used; the initial speed was set at 2.5 m/s, followed by 3.3 m/s, 4.1 m/s, 5.0 m/s, 6.6 m/s, and 8.4 m/s. There was a significant influence of exercise itself on plasma glucose and L-lactate concentrations and on heart rate (p < 0.05), whereas the amount of MD administered changed only the cortisol levels (p < 0.05). During rest and exercise, the variables remained within the normal reference range for stalled and exercising horses, respectively. Blood glucose levels in the placebo group at rest, 5.0 m/s, and 8.4 m/s were 87.63 ± 3.25 mg/dL, 78.33±10.08 mg/dL, and 95.18 ± 14.73 mg/dL, respectively, whereas those for the group supplemented with 200 g MD were 99.25±12.19 mg/dL, 79.55±13.81 mg/dL, and 97.30 ± 16.46 mg/dL, respectively. The mean cortisol levels in the placebo and 200 g MD groups at 8.4 m/s were 1.20 ± 0.53 mmol/L and 5.54 ± 4.73 mmol/L, respectively. In conclusion, MD supplementation increased serum cortisol levels and showed no effect on heart rate, blood glucose, L-lactate and serum insulin levels of horses submitted to an incremental exercise test.