Impact of using a fast-freezing technique and different thawing protocols on viability and fertility of frozen equine spermatozoa.

The effects of freezing technique and thawing protocol on thawed semen viability and fertility were studied. Ejaculates from 5 stallions (n = 25) were frozen by conventional or a fast-freezing technique. Frozen semen was thawed by two thawing protocols (37 °C 30 s(-1) or 75 °C 7 s(-1) ). Thawed semen was evaluated by progressive motility, vigour, morphology and plasma membrane integrity. Mares (n = 25) were inseminated with 300 (n = 11) or 150 (n = 14) million spermatozoa. A greater (P < 0.05) vigour and progressively motile spermatozoa were detected, respectively, at thawing and after 20 min post-thawing in the fast-freezing technique than in the conventional one. Plasma membrane integrity was also greater (P < 0.05) in semen frozen with the fast-freezing technique. Semen viability was not affected by thawing protocol. Pregnancy rate using the fast-freezing technique was 76% (19/25), and did not differ (P > 0.05) between insemination doses. We concluded that the 150 million progressively motile spermatozoa per dose using a deep-horn insemination maximises the use of equine semen. The fast-freezing technique, as compared to the conventional one, efficiently preserves the viability and fertilising capacity of spermatozoa, indicating a new method to improve the fertility of frozen equine semen.