Semen quality, lipid peroxidation, and seminal plasma antioxidant status in horses with different intensities of physical exercise

The aim of this study was to compare markers of semen quality, sperm membrane damage, and the seminal plasma antioxidant activity in warmblood stallions with and without sport workload stress. Four stallions were used for breeding only (control) and four both for breeding and competition in jumping. Semen samples were collected at 14-day intervals (from June to August) from each stallion (5 ejaculates per stallion). Immediately after sperm collection, a conventional examination of the ejaculate was processed. Catalytic activities of enzymes aspartate aminotransferase, alanin aminotransferase, glutathione peroxidase, superoxide dismutase and indicator of lipoperoxidation - F2(alpha) isoprostanes were measured in samples of seminal plasma. Contrary to basic semen quality indicators, the values of seminal plasma pH, aspartate aminotransferase and alanin aminotransferase were significantly (P < 0.05) impaired in the physically stressed stallions. Also, the level of F2(alpha) and the activity of superoxide dismutase were significantly (P < 0.05) increased by stress. The antioxidant activities of superoxide dismutase and glutathion peroxidase increased during the monitored period and reflected changes in F2(alpha) isoprostane concentration. We can conclude that even the conventional basic sperm indicators stay within the reference ranges of the biochemical indicators of seminal plasma such as pH or AST/ALT activity may be negatively influenced by sport workload stress. Increased concentrations of F2 alpha isoprostanes indicate that lipoperoxidation can be a mechanism of cell membrane destabilization, which is counteracted by an increase of antioxidant enzyme activities. This is the first report of oxidative stress symptoms in normospermic equine semen in relation to stallion sport workload.