Effect of thawing methods on frozen semen quality of yak (Poephagus grunniens L.) bulls

Aim: To evaluate different thawing temperatures and duration on the post-thaw semen quality of Indian yaks bulls. Materials and Methods: Semen ejaculates from four different yak bulls were collected using artificial vagina method and extended with tris extender containing 6.4% glycerol at 35 degrees C, cooled gradually from 35 degrees C to 5 degrees C at 1 degrees C/3 min and equilibrated at 4-5 degrees C for 4 h and frozen in French mini straws using a programmable bio-freezer and finally stored in liquid nitrogen. Thawing of frozen semen straws was carried out using three methods i.e., 35 degrees C for 60 s (thawing method I), 37 degrees C for 30 s (thawing method II) and 75 degrees C for 9 s (thawing method III). The post-thaw semen quality parameters assessed were sperm motility, percent live sperm, hypo-osmotic swelling test (HOST)-reacted sperm, acrosomal changes, and alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities in the extracellular media. Results: The percent sperm motility, total incidence of acrosomal changes, and extracellular release of AST varied significantly (p<0.01) between thawing methods but live sperm and HOST-reacted sperm did not vary significantly between thawing methods. The percent sperm motility of frozen yak semen for thawing method III was significantly (p<0.05) higher than that for thawing methods I and II, the difference between thawing methods I and II being non-significant. The critical difference test revealed that the total incidence of acrosomal changes and extracellular release of AST were significantly (p<0.05) lower when thawing was done using methods I and II than in method III. Conclusion: On the basis of the present experiment, we can conclude that barring the post-thaw sperm motility, thawing of frozen yak semen in water either at 35 degrees C for 60 s or 37 degrees C for 30 s gives better post-thaw semen quality than at 75 degrees C for 09 s.