Effect of antioxidant supplementation on oxidative stress in young exercising horses

Abstract

The production of reactive oxygen species (ROS) increases with exercise. An excess of ROS compared to antioxidants, known as oxidative stress (OS), can contribute to inflammation and diseases detrimental to horse performance. Our objective was to evaluate the effect of an antioxidant supplement on OS in young horses beginning training. 18 horses (10 geldings, 8 mares; age 29.0±6.5 months; BW 457.6±45.4 kg; BCS 5.5±0.6) were blocked by age and sex into 2 treatments groups; supplement (SUPP) or placebo (CON). After treatment began, horses underwent 30 days at maintenance followed by 30 days at moderate work. On days 30 and 60, horses completed a standardized exercise test (SET). Blood samples were collected once on day 0, before each SET (PRE), and 0 (POST), 1 (1h), and 24 hours (24h) after. Plasma was analyzed for glutathione peroxidase activity (GPX), superoxide dismutase activity (SOD), and thiobarbituric acid reactive substances concentration (TBARS). Horses were recorded at the walk (W) and trot (T) to determine stride duration (SD), and knee and hock range of motion (KRM, HRM) using motion analysis software. Data were analyzed using mixed linear models with type II ANOVA and estimated marginal means. There was a time effect for GPX (p<0.001), SOD (p=0.041), and TBARS (p<0.001). Compared to d30-PRE, GPX was still elevated at d30-1h (p=0.026) and TBARS did not recover until d30-24h (p=1.00). On d60, GPX (p=0.771) was unchanged and TBARS recovered by d60-1h (p=1.00), suggesting conditioning led to greater antioxidant capacity. Over all time points, TBARS tended to be lower for SUPP than CON (p=0.071). Treatment x day effect was significant for T-KRM (p=0.014) and a trend was found for W-DUR (p=0.099) and W-HRM (p=0.061), suggesting SUPP mitigated some decreases in mobility. Day had an effect on T-SD (p<0.001), W-KRM (p<0.001), and T-HRM (p<0.001), indicating reconditioning may have led to restricted movement. In conclusion, though the most significant changes to antioxidant status were due to reconditioning, SUPP mitigated aspects of exercise-induced OS and related changes in movement in young horses undergoing training.