Factors influencing the somatic cell nuclear transfer efficiency in pigs

Using a data set from our laboratory, we assessed the effects of several factors on pig cloning efficiency. The results demonstrated that cells at high confluence (>90%) used as donor cell resulted in higher pregnancy rate, delivery rate and overall cloning efficiency (number of live offspring born per reconstructed embryo transferred to recipients) compared with the cells at 60% to 79% confluence and 80% to 89% confluence. Cells with four, five and six passages compromised the pregnancy and delivery rates compared with first passage cells. The number of blastocysts transferred by somatic cell nuclear transfer (SCNT) did not significantly affect the cloning efficiency, but transfer of blastocyst derived from in vitro culture 5 d after SCNT achieved a significantly higher pregnancy rate compared with one to two cell SCNT embryos from overnight culture. The highest pregnancy rate, delivery rate and the largest litter size were obtained when Bama Miniature pig fibroblasts were used as donor cells and Landrace/Yorkshire hybrid gilts were used as recipients. Recipients treated with chemicals for estrus synchronization had higher pregnancy rates compared with untreated recipients. Our data might be helpful for improving SCNT efficiency in pigs.