Improving the post-thaw viability of cryopreserved stallion spermatozoa
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The present study was to improve the success for the cryopreservation of stallion spermatozoa, especially as the costs of using low post-thaw motility or sub-optimal fertility deters owners and breeders from using frozen semen. The aim was to develop a freezing extender/process that supports cell survivability throughout the freezing. Eleven stallions were collected and frozen in INRA 96 with two different concentrations of glycerol added. The mean post-thaw motility as assessed by percent alive (57.93% and 66.50%) was significantly (p<0.05) higher for two experimental glycerol concentrations (3.5% and 6.0%) when compared to the control, Minitube Cryoguard egg-yolk extender (39.71%). The Minitube semen freezing protocol has been one of the processes that we typically use for freezing equine spermatozoa. The addition of glycerol (6.0% concentration) to INRA 96 had the highest survivability and was used in the fertility trials. To evaluate the fertility of the frozen semen, eight mares were bred over two cycles with both fresh and frozen semen. The pregnancy rate of mares bred with frozen semen (55.56%) was not statistically (p<0.05) different from the pregnancy rate of mares bred with fresh semen (55.56%). INRA 96 with 6.0% glycerol improved the survivability of stallion spermatozoa through the cryopreservation process, and subsequent fertility was not statistically (p<0.5) different from fresh, extended semen.