Oxidative Stress and Antioxidant Supplementation of Horses During Endurance Exercise

To compare effects of a dietary supplement containing vitamin E alone or vitamin E plus vitamin C on antioxidant status, oxidative stress and membrane leakage during endurance exercise. A nutritional pre-competition survey allowed horses to be paired and randomly assigned to two groups. Three weeks prior to the competition, one group (E) was orally supplemented with 5,000 IU vitamin E/d, the other group (EC) with 5,000 IU vitamin E plus 7 g vitamin C/d. The ride covered 80 km of varying terrain. Blood samples, temperature and heart rate were taken the day before the race, 21 and 56 km during the ride, at completion, and after 20 min of recovery. Plasma lipid hydroperoxides (LPO), α-tocopherol (α-TOC), total ascorbate (ASC), albumin (ALB), creatine kinase (CK), and aspartate aminotransferase (AST), RBC and WBC total glutathione (GSH-T) and glutathione peroxidase (GPx) were analyzed. Thirty-four horses completed the race, 12 horses did not finish for reasons including lameness, metabolic problems, and rider option. Treatment had no significant effect on any of the variables measured, except for ASC, which had a treatment effect (P = 0.045). Creatine kinase, AST, RBC GPx, WBC GSH-T, and LPO increased, but RBC GSH-T and WBC GPx decreased with distance (P < 0.0001). Positive correlations were found for plasma LPO on CK (r = 0.25; P = 0.001) and AST (r = 0.33; P < 0.001). Positive correlations establish an association between muscle leakage and a cumulative index of oxidative stress. No advantage was found for EC over E, but comparison with previous studies suggest that the combination may be beneficial during more strenuous races.