Post-cooling sperm processing can rescue sperm quality of cooled-stored stallion semen.

The study investigates the usefulness of post-cooling sperm processing in improving the quality and fertility rates of cooled-stored stallion semen for artificial insemination.

About the Research

This research is focused on rectifying a problem that has been identified in equine reproduction: cooled-shipped semen often results in suboptimal fertility in horses. To do this, the researchers conducted a series of experiments to understand whether post-cooling sperm processing could enhance the quality of cooled-stored semen.

Operations and Experiments

• The research was conducted across four experiments. In all cases, they collected ejaculates, processed these, and diluted in a skimmed milk-based (SM) medium before storing at 5°C over 24 hours.
• In the first experiment, cooled-stored semen from 16 stallions was processed using a SpermFilter or centrifugation and then resuspended in an egg yolk-based freezing medium containing infiltrating cryoprotectants. The researchers checked sperm recovery and motility parameters immediately after sperm resuspension in both groups and compared with unprocessed samples.
• The second experiment followed similar methods but involved cooled semen samples from six different stallions. The research in this case compared three groups: unprocessed, SM, and the egg yolk-based medium.
• The third experiment cooled semen from four stallions, processing with a SpermFilter, before resuspending in the SM, egg yolk-based medium, or an egg yolk-based medium without cryoprotectants. These were also put through a thermoresistance test.
• The final experiment involved 39 estrous cycles of 11 mares being inseminated with either unprocessed cooled-stored semen or semen cooled and then processed by a SpermFilter and resuspended in one of the following: SM, the egg yolk-based medium with or without cryoprotectants, or centrifuged and resuspended in egg yolk-based medium.

Results

• General findings revealed that after processing and resuspension, semen in egg yolk mediums (with or without cryoprotectants) improved sperm parameters compared to unprocessed semen.
• A larger percentage of sperm was recovered following centrifugation than with the SpermFilter.
• Sperm resuspended in the egg yolk-based medium without cryoprotectants also showed better parameters throughout the thermoresistance test than the other groups.
• The fertility rates were similar across all groups, providing no significant advantage in one method over the others.

Conclusion

This study provides evidence to help improve the quality of cooled-stored stallion semen for artificial insemination. Specifically, enhancing the sperm processing and resuspension in egg yolk medium procedure resulted in improvement of sperm parameters. These findings could assist in rectifying the problem of poorer fertility rates with cooled-shipped equine semen.