Oxidative Stress in Horses in Three 80 km Races

Oxidative stress and muscle membrane leakage were compared in horses finishing (F; 24) or not finishing (NF; 16) in Research Ride 2002 (R2). These data were also compared to previous rides—Old Dominion (OD; more competitive) and Research Ride 2001 (R1; less competitive). For R2, blood samples were taken before (PRE), 27, 48 and 80 km, and 170 to 190 min during recovery. Blood was analyzed for plasma lipid hydroperoxides (LPO), α-tocopherol (α-TOC), creatine kinase (CK), aspartate aminotransferase (AST), and red and white blood cell (RBC and WBC, respectively) total glutathione (GSH-T) and glutathione peroxidase (GPx). Activities of CK and AST were higher (P < 0.05) before, during and after the ride in NF than in F. In R2, increases were found for RBC and WBC GSH-T, LPO, CK, and AST (P < 0.001); decreases for RBC and WBC GPx, and α-TOC (P < 0.001) as compared to the PRE sample. Correlations were found between RBC GPx and GSH-T with CK and AST, and these associated oxidative stress and muscle leakage. Values of CK, LPO and RBC GPx and GSH-T were higher (P < 0.05) in R2 than R1 or OD. High CK values during and after a race were found in F as well as NF horses. Thus CK was a better indicator of lack of fitness before than during a race. Overall, comparison of races revealed inconsistencies with difficulty and competitiveness, which suggests the need to consider other factors, such as the horse’s fitness, terrain and ambient conditions.