The effect of length of cryopreservation on the viability of bovine embryos in a commercial operation

A total of 2,232 bovine embryos was obtained from 294 flushings at a commercial embryo transfer operation. The embryos were frozen in groups from individual flushings using 0.25-cc straws and a conventional freezing procedure with glycerol as a cryoprotective agent. The embryos were stored in liquid nitrogen for up to 28 months. Sucrose was used for the removal of glycerol after the thawing of embryos. The thawed embryos were then examined morphologically, and 1,097 embryos (49%) with no apparent defects were used for subsequent transfer. The viability of the thawed embryos from the individual flushes was evaluated in relationship to the length of cryopreservation. No correlation (P > 0.1) was found between the two parameters in embryos from superovulations with above and below average yields. This finding was further confirmed in a proportion of the embryos by the evaluation of pregnancy rates. Thus, neither the typical length of embryo storage in a commercial operation nor the success of superovulation influenced the survival rate of embryos after thawing based on morphological criteria and pregnancy rates.