Freezing Hu ram semen: influence of different penetrating cryoprotectants and egg yolk level on the post-thaw quality of sperm.

Objective: The Hu sheep is a renowned breed known for its high reproductive rate. It is in estrus all year round, and its breeding population is gradually expanding. However, the current techniques for cryopreserving semen have limited effectiveness, which hinders the continuous development of this species. The purpose of this study is to explore the effects of different penetrating cryoprotectants (CPAs) and egg yolk (EY) concentrations on the cryopreservation of Hu ram semen to determine the most effective combination.

Methods: In this study, the effects of glycerol (GLY), ethylene glycol (EG), dimethylacetamide, dimethyl sulfoxide, different proportions of GLY and EG, EY on sperm quality after thawing were investigated by detecting sperm total motility (TM), progressive motility (PM), straight-line velocity, curvilinear velocity, average path velocity, amplitude of lateral head displacement, wobble movement coefficient, average motion degree, functional integrity (plasma membrane integrity, acrosome integrity) and reactive oxygen species (ROS) level.

Results: When GLY and EG were added together, compared to other concentration groups, 6% GLY significantly (p<0.05) increased TM, PM, plasma membrane integrity, and acrosome integrity of thawed sperm. Additionally, it significantly (p<0.05) decreased the ROS level of sperm. In this study, the TM, PM, and membrane integrity of the 6% EG were significantly (p<0.05) higher than those of the control, 1% GLY+5% EG and 6% GLY+6% EG groups. Compared to other concentration groups, 20% EY significantly (p<0.05) improved the TM, PM, and plasma membrane integrity of thawed sperm. However, the integrity of the acrosome increased with the higher concentration of EY.

Conclusion: In conclusion, the post-thawed Hu ram semen diluted with a diluent containing 6% GLY and 20% EY exhibited higher quality compared to the other groups.