Forced Collapse of the Blastocoel Cavity Improves Developmental Potential in Cryopreserved Bovine Blastocysts by Slow‐Rate Freezing and Vitrification

This study was conducted to evaluate the effectiveness of forced collapse of the blastocoel before slow‐rate freezing and vitrification of bovine blastocysts. Cryopreservation of bovine blastocysts has been proposed as a tool to improve the feasibility of cattle production using the embryo transfer technique. However, the low efficiency of frozen–thawed embryos survival and further development is a crucial problem. In this study, bovine in vitro and in vivo blastocysts were slow‐rate frozen and vitrified after forced blastocoele collapse (FBC) of the blastocyst cavity by puncturing the blastocoele with a pulled Pasteur pipet. Differences in the developmental potential of frozen–thawed blastocysts derived from FBC and non‐FBC groups were found in both slow‐rate freezing and vitrification. Furthermore, we found that the total cell number of blastocysts in FBC groups was increased and the index of apoptosis in FBC groups was decreased. Consistent with these results, real‐time RT‐PCR analysis data showed that expression of the anti‐apoptotic Bcl‐XL gene was significantly increased by FBC groups, whereas expression of the pro‐apoptotic Bax gene was significantly decreased by FBC groups. Our results also showed that pregnancy outcomes in both slow‐rate frozen and vitrified bovine in vivo blastocysts could be improved by reducing the fluid content after FBC of the blastocyst cavity. Therefore, we suggest that FBC of the blastocyst cavity with a pulled Pasteur pipet is an effective pre‐treatment technique for both slow‐rate freezing and vitrification of bovine blastocysts.