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.

BACKGROUND: Post-diluents could potentially increase semen cryotolerance, but remain poorly explored in horses. OBJECTIVE: The aim was to evaluate the efficiency of post-diluents on frozen-thawed semen viability of two stallions (S1-S2). MATERIALS AND METHODS: The cryopreserved semen was thawed at 50°C for 40 seconds. Semen motility and acrosin activity (AA) were determined during the thermo-resistance test (TRT). RESULTS: Progressive motility of S2 semen decreased after 60 and 90 minutes of TRT (TRT60 and TRT90) on the control compared to both post-diluents. The total motility of both S1 and S2 decreased on TRT60 and TRT90 semen control versus both Ringer and Merk post-diluents. The AA on S1 was higher than S2 throughout the TRT. Pregnancy rates after artificial insemination (AI) were similar among post-diluents and stallions. CONCLUSION: Post-diluents do not contribute to predicting frozen-thawed semen fertility or the efficiency of equine AI.