Effects of vitamin E supplementation in the extender on frozen-thawed bovine semen preservation

The maturing sperm cells discard the majority of their cytoplasm during the final stages of spermatogenesis and lose some of their defense enzymes. The purpose of this study was to investigate the effects of vitamin E supplementation on standard semen quality parameters and antioxidant activities of frozen-thawed bovine sperm. Vitamin E was added at concentrations of 0.5, 1.0, 1.5 and 2.0 mg/ml to bovine semen cryoprotective medium. The results showed that the sperm motility and VSL, STR values in the extender supplemented with 1.0 and 1.5 mg/ml of vitamin E, were significantly higher than that of other concentrations (P < 0.05). The percentages of acrosome-intact and membrane-intact sperm were significantly improved (P < 0.05) by supplementing with 1.5 mg/ml of vitamin E. In biochemical assays, the extender supplemented with vitamin E did not exhibit significant improvement in SOD (superoxide dismutase) levels, compared with the control (P > 0.05). Compared with other groups, CAT (catalase) levels were demonstrated to be greater with the supplementation of vitamin E at 1.0 and 1.5 mg/ml (P < 0.05). The extender supplemented with 1.5 mg/ml of vitamin E caused the highest levels of glutathione peroxidase (GSH-Px), compared with other groups (P < 0.05). The glutathione (GSH) activity was significantly higher with the supplementation of 0.5, 1.0 and 1.5 mg/ml of vitamin E, compared with 2.0 mg/ml in the vitamin E group and control (P < 0.05). Moreover, increasing the doses of vitamin E decreased sperm antioxidant activities, the extender supplemented with 2.0 mg/ml of vitamin E, caused the lowest levels of GSH-Px and GSH activities, compared with other treatment groups (P < 0.05). In conclusion, the beneficial effects of vitamin E noted in this study can be attributed to the antioxidant characteristics. Vitamin E supplementation in the extender reduced the lipid peroxidation potential and improved semen quality during freezing-thawing. More researches are needed to evaluate and understand the precise physiological role of vitamin E in reproduction.