Using a data set from our laboratory, we assessed the effects of several factors on pig cloning ef?ciency. The results demonstrated that cells at high con?uence( > 90%) used as donor cell resulted in higher pregnancy rate, delivery rate and overall cloning ef?ciency(number of live offspring born per reconstructed embryo transferred to recipients) compared with the cells at 60% to79% con?uence and 80% to 89% con?uence. Cells with four, ?ve and six passages compromised the pregnancy and delivery rates compared with ?rst passage cells. The number of blastocysts transferred by somatic cell nuclear transfer(SCNT) did not signi?cantly affect the cloning ef?ciency, but transfer of blastocyst derived from in vitro culture 5 d after SCNT achieved a signi?cantly 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 ?broblasts 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 ef?ciency in pigs.
