Aim: This study aimed to study the electrophoretic properties of seminal plasma and sperm proteins of Black Bengal buck semen and their correlation with in vitro sperm characters and freezability.
Materials and methods: Semen ejaculates from nine Black Bengal bucks were collected by artificial vagina (n=20/buck). Ejaculates were evaluated for in vitro sperm characters and electrophoretic profile of seminal protein. In vitro sperm characters were evaluated immediately after collection, after completion of equilibration period, and after freeze-thawing. For seminal protein studies, seminal plasma proteins were precipitated by ice-cold ethanol method, and sperm proteins were extracted by Triton X detergent extraction method. Discontinuous sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was performed to assess the molecular weight of seminal proteins. Correlation between in vitro sperm characters and protein bands was determined by Pearson's correlation coefficient, and two-way ANOVA was applied to find the individual buck differences.
Results: Significant difference (p<0.01) among the bucks was noticed in the in vitro sperm characters evaluated at all the three stages of semen evaluation such as immediately after collection, after completion of equilibration period, and post-freeze thawing. Progressive loss of sperm motility, membrane integrity, and other in vitro sperm characters were noticed during cryopreservation. A total of ten protein bands in the molecular weight ranging from 17 to 180 kDa were found in the SDS-PAGE of seminal plasma proteins, while nine bands of 17-134 kDa were observed in sperm proteins. Seminal plasma proteins of molecular weight 75, 62-49, 20, and 17 kDa and sperm proteins of 75, 20, and 17 kDa were present in all the nine bucks (100%) screened, and variation among the bucks was noticed for the presence of other proteins. Seminal plasma protein of 180-134 kDa showed a negative correlation with individual motility (-0.716) and functional membrane integrity of sperm cells (-0.724) in post-freeze-thaw analysis and 48 kDa protein had a positive correlation with individual motility (0.649) and functional membrane integrity of sperm cells (0.664) in post-thaw analysis. Sperm proteins of 63 kDa had a negative correlation (-0.616) with sperm concentration in neat semen.
Conclusion: Variation among the bucks was noticed in the in vitro sperm characters and semen freezability. Correlation between seminal proteins and in vitro sperm characters and semen freezability had been found which might be useful as a tool to select breeding bucks.
Keywords: buck; in vitro characters; semen; seminal proteins.