SUMMARY Two hundred and twenty five morulae were submitted to a ultra rapid freezing in four different treatments. In treatment I (n=57), the embryos were first exposed to a 5.0M glycerol pre treatment, and later to a glycerol 5.0M + lactose 0.25M freezing solution. In the treatment II (n=54) the procedure was similar to the treatment I, but with 0.5M of lactose instead 0.25M. In the treatment III (n=57), the embryos were exposed directly to a glycerol 5.0M + lactose 0.25M freezing solution. In the treatment IV (n=57) the procedure was similar to the treatment III, but with lactose 0.5M instead 0.25M. The embryos were maintened 5 minutes in each solution, and then loaded in groups of 6 to 12, in 0.25ml plastic straws. After thawing in a water bath at 37 °C, the cryoprotector was removed by five minutes exposure to a lactose solution in the same concentration than that used in the freezing procedure. After 48 hours of culture, the highest viability was observed in treatment IV (80.7%), followed by treatment III (66.7%), treatment II (66.7%) and treatment I (31.6%). Pretreatment determined a decrease in the viability (49.2%) when compared with the viability of groups without pre treatment (73.7%). The embryo viability was higher with lactose 0.5M (73.7%) than with lactose 0.25M (49.2%).
ultra rapid freezing; pretreatment; lactose
