HIGH FERTILIZING ABILITY OF MOUSE SPERMATOZOA DILUTED SLOWLY AFTER CRYOPRESERVATION

Mouse epididymal spermatozoa in cryopreservation solution (18% raffinose and 3% skim milk in distilled water) were frozen and stored at -196-degrees-C , and later thawed at room temperature. After thawing, the sperm suspension was diluted either quickly or slowly, and the effects of dilution speed on sperm motility and fertilizing ability were examined. There was no difference in motility between the slowly diluted and quickly diluted spermatozoa, but there was a significant difference in fertilizing ability, with greater fertility in the slowly diluted spermatozoa. These results indicate that slow dilution after thawing prevents the sharp change in osmolarity and viscosity between the cryopreservation solution and diluent. Furthermore, slow dilution protects the fertilizing capacity of frozen-thawed mouse spermatozoa.