Survival of bovine embryos stored at 4°C

These experiments were designed to test the efficacy of storing bovine embryos at 4°C. Of particular interest were the age of embryo at which maximum post-storage survival could be achieved and longevity at 4°C. A greater proportion of day 8 blastocysts developed in vitro at 37°C following refrigeration for 48 hr than did embryos collected 2, 4 or 6 days after estrus (P<0.01). Survival of blastocysts stored at 4°C for 48 hr was similar to that of nonstored blastocysts. In a subsequent experiment, day 8 blastocysts were recovered nonsurgically and assigned to one of the following treatments: (a) immediate transfer; (b) culture at 37°C; or (c) storage at 4°C for 1, 2, 3 or 5 days. Post-storage viability was assessed by either development in culture at 37°C or embryo survival following nonsurgical transfer to synchronized recipients. In vitro survival of nonstored embryos and embryos stored 1 day did not differ. Survival decreased after storage for 2 days (P<0.10) or longer (P<0.05). Similar results were observed for survival after transfer, but embryo viability decreased even more rapidly with increasing duration of storage. In vitro survival was approximately 50% for blastocysts stored for 3 and 5 days, but few pregnancies resulted from transfer of embryos stored for these periods. In another experiment survival after transfer of blastocysts stored at 4°C for up to 2 days was similar to that of nonstored blastocysts.