Two step freezing of cow embryos in 1.4 M glycerol.

Day 6 1 2 -7 1 2 cow embryos were frozen in 1.4 M glycerol in PBS, at 0.3 degrees C/min to -30 (group I), -35 (group II), and -40 degrees C (group III) before being plunged into liquid nitrogen. They were subsequently thawed by direct transfer to water at 37 degrees C. In Experiment I, embryos frozen and thawed were cultured in vitro, 12 out of 19 embryos (63%) survived and there were no significant (p > 0.05) differences in survival rates among the three freezing groups. In Experiment II, 29 embryos frozen to -30 or -35 degrees C were transferred non-surgically to heifers on day 7. Seventeen of 29 recipients (59%) were pregnant at day 60. Five embryos frozen to -35 degrees C resulted in 5 pregnancies (100%) after thawing and surgical transfer.