Frozen Storage and Transfer of Bovine Embryos

Abstract

Viability of bovine embryos after freezing and thawing was studied to determine the optimal stage of development for freezing and requirements for synchrony of recipient and embryo for successful transfer. There was no significant difference in viability of frozen-thawed blastocysts obtained on day 7 and 8 after estrus providing they were enclosed in the zona pellucida. Pregnancy rates in recipients synchronous with the age of the embryo and those 1 day earlier in an estrous cycle were similar. Overall, 52% of frozen embryos continued normal development in vitro and 40% resulted in pregnancies when transferred to recipients. Fewer day 8 embryos which were free from the zona (hatched) developed in vitro after freezing (25%) and no pregnancies were obtained after 10 embryos were transferred to recipients. Embryos obtained 11 to 13 days after estrus developed normally in vitro after exposure to 2M DMSO, seeding at −7 C and freezing to −20 C but survival was low after freezing to −110 C and storage at −196 C. Freezing rates between 1 and 2.4 C/min and concentrations of DMSO between 1.0 and 3.0 M had no marked effect on survival of embryos but there was a tendency for higher survival rates with rapid thawing. It is concluded that the optimal stage for freezing bovine embryos is the blastocyst prior to hatching. For transfer after thawing, recipients may be either synchronous or a day earlier in an estrous cycle than the donor of the embryos. Copyright © 1978. American Society of Animal Science . Copyright 1978 by American Society of Animal Science.