Computerized staged-freezing technique improves sperm survival and preserves penetration of zona-free hamster ova.

Sperm cryosurvival was evaluated after a staged freezing program, compared with standard vapor-cooling. Fifty-nine ejaculates produced by nine proven fertile males were studied before and after preservation with glycerol or dimethylsulfoxide. Spermatozoal survival was assessed by after-thaw motility, mean sperm velocity (MSV) with the use of multiple exposure photography and by the ability to penetrate zona-free hamster ova. A significantly greater reduction in sperm motility was observed with the addition of DMSO in contrast to G (P less than 0.01). All freezing methods resulted in reduced sperm motility, compared with unfrozen samples. The after-thaw sperm motility was significantly lowered when vapor-freezing was used in comparison with the staged process (22.9% +/- 2.6% versus 32.9% +/- 3.4%; P less than 0.01). The MSV was slightly, but not significantly, lower in the after-thaw semen, compared with fresh ejaculates. A significant impairment in sperm penetration ability was evidenced with vapor-freezing, compared with the staged cooling (25.7% +/- 3.1% versus 34.9% +/- 3.0%; P less than 0.01). The programmed freezing process rendered the same sperm efficiency in penetrating zona-free hamster ova as did the fresh samples. This relatively rapid, simple, and reliable computerized cooling technique improves the efficiency of sperm cryostorage and preserves its penetration capacity.