Freezing of Stallion Semen: in vitro and in vivo Evaluation of Sperm Motility and Acrosin Activity in Frozen-thawed Semen with Addition of Post-diluent Extenders.

This research explored the effects of post-diluents on the quality of frozen and thawed stallion semen, focusing on sperm motility and acrosin activity. However, the results indicate that these additives do not appear to have a significant impact on semen fertility or the success rate of artificial insemination in horses.

Objective and Methodology

• The study aimed to assess the impact of post-diluents on the viability of frozen-thawed stallion semen. The researchers hypothesized that these substances might enhance the cryotolerance (resilience to freezing and thawing) of the semen, but this area had not been much explored in equine studies before.
• The research involved two stallions (referred to as S1 and S2), whose cryopreserved semen samples were thawed rapidly at a temperature of 50 degrees Celsius for a brief span of 40 seconds.
• Key metrics assessed for semen quality were sperm motility (movement ability, a vital factor for reaching and fertilizing the egg) and acrosin activity (AA, an enzyme that plays a crucial role in egg penetration).

Results and Findings

• During a thermo-resistance test (TRT) that measures how sperm endure under different temperatures, the researchers found various results for the two stallions. S2’s sperm exhibited reduced progressive motility (the ability to move forward in a straight line, an important aspect of fertilization) after 60 and 90 minutes into the TRT, when compared with samples using post-diluents.
• However, for the total motility (overall movement capability, regardless of direction) of both stallions’ semen samples, a decrease was observed on the 60- and 90-minute marks of the TRT when compared against both Ringer and Merk post-diluents.
• The study discovered that acrosin activity for S1 was consistently higher than S2 throughout the TRT, suggesting individual differences between stallions in this aspect.
• Crucially, there was no significant difference in regard to pregnancy rates achieved through artificial insemination (AI) among the various post-diluents and stallions.

Conclusion

• The results suggested that the addition of post-diluents does not improve the prediction of the fertility of frozen-thawed stallion semen, nor does it contribute significantly to the efficiency of AI in horses.
• This information could be helpful for reproductive veterinary practitioners, horse breeders, and other equine professionals when deciding on the most effective semen preservation and AI techniques to employ.