The cryoprotective effects of ascorbic acid supplementation on bovine semen quality

To investigate the effects of ascorbic acid supplementation on standard semen quality parameters and antioxidant activities after thawing of bovine frozen semen, antioxidant ascorbic acid was added at concentrations of 2.5, 4.5, 6.5 and 8.5 mg/ml to bovine semen cryoprotective medium. The results showed that the sperm motility and motion characteristics were improved in the presence of ascorbic acid in extender, as compared to the control. The motility and straight linear velocity (VSL), linearity index (LIN), average path velocity (VAP), wobble coefficient (WOB), lateral head displacement (ALH) values and the percentage of "grade A" sperm in the extender supplemented with 4.5 mg/ml ascorbic acid were significantly higher than that of other treatment groups (P<0.05). The acrosome integrity and membrane integrity were significantly improved (P<0.05) by supplementing with 4.5 mg/ml ascorbic acid in the extender compared with a control. The extender supplemented with ascorbic acid did not lead to any improvement in superoxide dismutase (SOD) levels. The catalase (CAT) activity was higher in the extender supplemented with ascorbic acid at 4.5 mg/ml, when compared with other groups (P<0.05) and the extender supplemented with ascorbic acid significantly decreased glutathione peroxidase (GSH-Px) activity, whereas reduced glutathione (GSH) activities were significantly enhanced, compared with the control (P<0.05). Increasing the doses level of ascorbic acid decreased GSH-Px and GSH activity, the supplementation of 8.5 mg/ml ascorbic acid produced the lowest level of GSH-Px and GSH activity among groups (P<0.05). The extender supplemented with ascorbic acid could reduce the oxidative stress provoked by freezing-thawing and improve bovine semen quality. The particular properties of ascorbic acid are poorly related to its effectiveness in membrane cryopreservation. Further studies are required to determine lipid peroxidation and antioxidant capacities of ascorbic acid in cryopreserved bovine semen.