Rapid thawing of rabbit embryos after storage at -196 degrees C

Rabbit morulae frozen to -25 degrees C and transferred from this temperature to -196 degrees C were thawed at different rates. Maximum survival of the embryos was obtained at thawing rate of 650 degrees C/min. Slower and more rapid thawing decreased the survival. At thawing rates of 25 degrees C/min and 1 550 degrees C/min all morulae died. The ability of morulae to develop after storage at -196 degrees C and thawing at 650 degrees C/min was assayed by culture in vitro and transfer into the recipients. Of 241 morulae obtained after thawing, 197 (81.7%) continued normal development. Of 100 unfrozen morulae, 97 (97%) developed to the blastocyst stage. Of 41 frozen and 20 unfrozen embryos transferred into the recipients, 28 (68.3%) and 19 (95%), respectively, implanted. After transfer of 37 blastocysts obtained by culture of morulae thawed at 650 degrees C/min, 5 recipients have born 21 (56.8%) live offspring.