Factors Influencing the Production Efficiency of Cloned Pigs: A Large-Scale Retrospective Analysis

Pig somatic cell nuclear transfer (SCNT) has valuable applications in agriculture, biomedicine, and life sciences, yet low cloning efficiency remains a major constraint limiting its application. To systematically investigate factors related to the production efficiency of pig cloning, this study conducted a retrospective analysis of 367,701 SCNT embryos transferred into 2019 surrogate sows over five years, focusing on breeds of donor cells, the season of embryo transfers, and the number of embryos transferred per surrogate. Our data demonstrate that the genetic background of donor cells is a critical determinant. SCNT embryos generated by wild-type (WT) Pietrain and Duroc pigs yielded significantly higher cloning efficiencies compared to those from Large White and Yorkshire pigs. This breed-specific influence was also observed with genetically modified (GM) donor cells. Nevertheless, within the GM groups, GM-Duroc and GM-Yorkshire showed superior efficiency compared to GM-Large White and GM-Bama. Furthermore, Summer was identified as the least favorable season for embryo transfer, with significantly lower pregnancy rates, delivery rates, and cloning efficiency compared to the other seasons. Importantly, we established that transferring 100-150 embryos per recipient optimized cloning efficiency, significantly outperforming groups receiving higher embryo numbers without compromising pregnancy rates, delivery rates, or average litter sizes. Our findings provide valuable guidance for optimizing large-scale SCNT protocols in swine.