Survival and viability of fresh and frozen-thawed in vitro bovine blastocysts.

Three experiments were undertaken to investigate the effect of some factors on survival and viability of bovine blastocysts produced in vitro in serum-free oviduct-conditioned media. In vitro survival to freezing was higher for blastocysts appearing on days 6 and 7 than for day 8 blastocysts (67 and 50% hatching rate vs 12%). Transfer success of day 8 blastocysts to recipient heifers was 35% (9/26) calves born vs 19% (4/21) for cows. Embryo mortality occurred mainly during the peri-implantation period (between days 21 and 45) for cows compared with heifers. Calving rate after direct transfer of frozen blastocysts without dilution was 24% (4/17) compared with 31% (5/16) for control unfrozen blastocysts.