[Cryoconservation of 8-celled stage rabbit embryos in an automated "open system"]

Rabbit embryos were successfully frozen at the 8-cell stage, employing a rapid and a slow freezing-thawing program. They were then stored at -196 degrees C (liquid nitrogen) for 10 to 60 days. After thawing the embryos were examined for viability in vitro and in vivo. Using the slow program B 82.5% were morphologically intact, compared to only 69.3% after the rapid procedure (program A). 88.8% of the group first mentioned above, and 56.8% of the latter developed to the blastocyst stage after 4 to 5 days in culture. The implantation rate was 18.1%, when embryos were transferred to minus 18 hours asynchronous recipients, after thawing. With 40%, a significantly higher implantation rate could be achieved, when the embryos were transferred to minus 24 hours asynchronous foster mothers. 18 viable young were born 30 to 32 days after transfer.