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

## TL;DR

This study identifies key factors affecting pig cloning success, including donor breed, season, and embryo numbers, offering practical guidance to improve cloning efficiency.

## Contribution

The study provides new insights into breed-specific effects and optimal embryo transfer numbers for pig cloning based on a large-scale retrospective analysis.

## Key findings

- Pietrain and Duroc donor cells yield higher cloning efficiency compared to Large White and Yorkshire.
- Transferring 100–150 embryos per surrogate optimizes cloning efficiency without compromising pregnancy or delivery rates.
- Summer is the least favorable season for embryo transfer, with lower success rates compared to other seasons.

## Abstract

Pig cloning is an important technology, but its low efficiency limits wider application. By analyzing five years of data involving over 2000 surrogate sows and 367,000 embryos, we identified several important factors affecting cloning success. We found that the breed of the donor cell significantly influences outcomes, with notable differences observed between breeds. Compared to Summer, the other three seasons are more suitable for embryo transfer. Interestingly, using fewer embryos (100–150 per surrogate) resulted in better efficiency than using larger numbers. This contrasts with recommendations from a decade ago, suggesting that optimal embryo numbers need continual adjustment as cloning techniques improve. Our findings provide clear, practical guidance to improve the production of cloned pigs for agriculture and biomedical research.

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.