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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 the present study was to investigate the effects of Vitamin E supplementation on standard semen quality parameters and anti-oxidant 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 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 Vitamin E.In biochemical assays, the extender supplemented with Vitamin E did not exhibit significant improvement in SOD levels, compared with the control (p>0.05).Compared with the other groups, CAT levels were demonstrated to be greater with the supplementation of Vitamin E at 1.0 and1.5 mg/ml (P<0.05).The extender supplemented with 1.5 mg/ml Vitamin E caused the highest levels of GSH-Px, compared with other groups (p<0.05).The GSH activity was significantly higher with the supplementation of 0.5, 1.0 and 1.5 mg/ml Vitamin E, compared with 2.0 mg/ml 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 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 the present study can be attributed to the antioxidant characteristics.Vitamin E supplementation in the extender reduced the lipid peroxidation potential and improved semen quality during the freezing-thawing.More researches are needed to evaluate and understand the precise physiological role of Vitamin E in reproduction.