Effect of evening primrose oil on biochemical parameters of thoroughbred horses under maximal training conditions

The antioxidative effect of evening primrose oil (EPO) administration on the oxidative stress of race horses during their regular training period was determined. The eight-week experiment was performed on ten clinically healthy thoroughbred horses. All the horses were enrolled in a regular training program. Eight weeks before the experiment, the horses were fed a diet which remained the same for the following eight weeks, only supplemented with 150 ml EPO (blood samplings 3 times). Total antioxidant reactivity (TAS), thiobarbituric acid reacting substances (TBARS), uric acid (UA) levels, activities of muscle enzymes - aspartate aminotransferase (AST), creatine kinase (CK), and parameters of fatty acid metabolism such as triacylglycerols (TAG) and nonesterified fatty acids (NEFA) were determined. Average values of TAS after supplementation with EPO rose gradually and were detected at significantly higher levels (P ≤ 0.05) in the sixth week in comparison with the control. The concentration of malondialdehyde, measured as TBARS, decreased significantly (P ≤ 0.05) compared with the untreated control. The activities of AST and CK fluctuated, but no disturbance was demonstrated in muscle homeostasis. The present results indicate that the total antioxidant activity of the thoroughbred horses fed a diet supplemented with EPO was higher, and it helped stabilize the permeability of the muscle cell membranes in the horses at full workload.