Effect of synchronization of donor cells in early G 1‐phase using shake‐off method on developmental potential of somatic cell nuclear transfer embryos in cattle

In this study, we compared the developmental ability of somatic cell nuclear transfer (SCNT) embryos reconstructed with three bovine somatic cells that had been synchronized in G0-phase (G0-SCNT group) or early G1-phase (eG1-SCNT group). Furthermore, we investigated the production efficiency of cloned offspring for NT embryos derived from these donor cells. The G0-phase and eG1-phase cells were synchronized, respectively, using serum starvation and antimitotic reagent treatment combined with shaking of the plate containing the cells (shake-off method). The fusion rate in the G0-SCNT groups (64.2 ± 1.8%) was significantly higher than that of eG1-SCNT groups (39.2 ± 1.9%) (P < 0.05), but the developmental rates to the blastocyst stage of SCNT embryos per fused oocytes were similar for all groups. The overall production efficiency of the clone offspring in eG1-SCNT groups (12.7%) per recipient cow was higher than that in G0-SCNT groups (3%) (P < 0.05). The mean birth weight of cloned calves and the average calving score in the G0-SCNT groups (48.1 ± 3.4 kg and 3.3 ± 0.3, respectively) was significantly higher (P < 0.05) than those of eG1-SCNT groups (37.2 ± 2.1 kg and 2.3 ± 0.2, respectively). Results of this study indicate that synchronization of donor cells in eG1-phase using the shake-off method improved the overall production efficiency of the clone offspring per transferred embryo.