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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 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.Keywords: bovine semen, vitamin E, cryopreservation, standard semen quality parameters, antioxidant activities ImplicationsBovine semen cryopreservation allows the widespread dissemination of valuable genetic material. However, the overproduction of reactive oxygen species (ROS) causes sperm membrane structural damage and results in the loss of 40% to 50% of viable sperm during freeze-thaw. As the primary component of the sperm antioxidant system, vitamin E is the major membrane protectant against ROS. No data seem to be available regarding the effects of vitamin E on frozen-thawed semen of the Chinese Holstein Cattle. This study was set up to determine the effects of vitamin E on standard semen parameters and antioxidant activities following the freeze-thawing of bovine semen.

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In the current study, the difference between the sex‐sorted and non‐sex‐sorted frozen semen of Holstein Friesian breed cattle was investigated. Significant variation (p < .05) was found in the semen quality parameters such as motility; vitality; acrosome integrity rate; the anti‐oxidative enzyme activity including GSH (glutathione); SOD (superoxide dismutase); CAT (catalase); GSH‐Px (glutathione peroxidase) and the rate of fertilization. The results showed that the sperm acrosome integrity and motility of the non‐sorted sperm were higher compared to sex‐sorted sperm (p < .05). The linearity index and mean coefficient analysis revealed that the percentage of ‘grade a’ in sex‐sorted sperm were significantly (p < .05) lower than non‐sorted sperm. Interestingly, low SOD level and high CAT level was found in the non‐sexed semen than in the sexed semen (p < .05). Furthermore, the GSH and GSH‐Px activity in the sexed semen was found lower than the non‐sexed semen (p < .05). In conclusion, sperm motility characteristics were lower in sex‐sorted semen than in non‐sex‐sorted semen. This might be related to the complex process of sexed semen production, which could reduce sperm motility and movement characteristics, acrosomal integrity, CAT, SOD, GSH and GSH‐Px, and finally lead to the decline in the fertilization rate.