Optimization of embryonic developmental stage, embryo transfer number, synchronization method for enhancing the efficiency of cloned Ỉ pig embryo transfer

The aim of this study was to establish suitable conditions for the transfer of cloned Ỉ pig embryos by determining the appropriate embryonic developmental stage, number of SCNT Ỉ pig embryos transferred, and synchronization method. Under the conditions of the present study, our results demonstrated that the transfer of SCNT-derived blastocysts resulted in a significantly higher pregnancy rate than the transfer of embryos at 20 h post-SCNT (P < 0.05). The transfer of 60 SCNT-derived blastocysts resulted in the lowest pregnancy rate (P < 0.05). Although variation in the number of blastocysts transferred (80, 100, 120, or 150) did not significantly affect pregnancy outcomes, none of the recipients receiving 80 SCNT-derived blastocysts subsequently farrowed. Increasing the number of SCNT-derived blastocysts transferred from 100 to 150 did not significantly affect the proportion of recipients that successfully farrowed. Estrus synchronization of recipients with PGF2α, followed by eCG and hCG administration, improved the efficiency of cloned pig embryo transfer. The pregnancy rate in recipients synchronized with PGF2α + eCG + hCG was significantly higher than that in the eCG + hCG group (P < 0.05). Under the conditions of the present study, synchronization with PGF2α, eCG, and hCG combined with the transfer of at least 100 SCNT-derived blastocysts appeared to provide a more favorable strategy for improving the efficiency of cloned Ỉ pig embryo transfer.