The effect of combined cryoprotectants on the cryotolerance of boar sperm.

Abstract

Objective: The frozen semen has the significant advantages of long-term storage and long-range transportation. However, due to the low cryotolerance of boar sperm, the global utilization of frozen boar semen in artificial insemination was less than 1% until the year 2000.

Methods: In this study, the effects of five cryoprotectants at different concentrations on the cryotolerance of boar semen were evaluated when they were added separately, and the optimal concentrations for each cryoprotectant were determined, then their combined additive effects were further assessed.

Results: At a glycerol (GLY) concentration of 5%, the quality of frozen-thawed sperm reached its maximum value, which was significantly higher than the 4% GLY group (p<0.05) and 0% GLY group (p<0.01). The straight-line velocity (VSL), curvilinear velocity (VCL), average path velocity (VAP), sperm plasma membrane integrity (SPMI), sperm acrosome integrity (SAI) and sperm mitochondrial activity (SMA) of the frozen-thawed sperm in treated egg yolk group exhibited significant improvements compared to the untreated egg yolk group (p<0.05). The total motility (TM), progressive motility (PM), SPMI, SAI, and SMA of 2% Equex STM paste group were significantly higher than the rest groups (p<0.05). The TM, PM, VSL, VCL, and VAP of frozen-thawed sperm in the 250 nM and 300 nM Mitoquinone mesylate groups showed significant improvements compared to the other groups (p<0.05), and the reactive oxygen species levels in sperm cells were also significantly lower (p<0.05). The quality of frozen-thawed boar sperm in 0.6 mM L-ergothioneine group reached its peak value and was significantly higher than the rest groups (p<0.05). When these five cryoprotectants were used in combination, the quality of frozen-thawed boar sperm exhibited a significant improvement compared to when they were used individually (p<0.05). Utilizing the frozen-thawed boar semen to inseminate estrus sows, the reproductive performance of the sows did not differ significantly from the sows inseminated with fresh semen (p>0.05).

Conclusion: The optimized boar semen cryopreservation system can substantially enhance the quality of frozen-thawed boar sperm, making it suitable for artificial insemination in pig farm.