Genetic connectedness and genotype-by-environment interaction in a maternal pig line across countries

Genetic connectedness between management units quantifies the extent to which estimated breeding values (EBV) can be accurately compared across management units or subpopulations. When there is a sufficient level of genetic connectedness, best linear unbiased prediction (BLUP) of EBV enables fair comparisons across these units. Genotype-by-environment (G × E) interaction can alter an individual's expression of genetic potential across environments, thereby compromising the accuracy of selection decisions. The aim of this study was to investigate the extent of genetic connectedness and G × E interaction for a maternal pig line between countries (France, China, and Thailand) for five traits: age at 100 kg (AGE), number of functional teats (NFT), birth weight (BW), backfat thickness at 100 kg (BFT), and number of piglets born alive (NBA). We observed high connectedness across the three countries, as reflected by high coefficient of determination (CD) values (ranging from 0.61 to 0.96) across all traits and time periods. For all traits, the pair France-China had higher CD values (0.80 on average) than the pair France-Thailand (0.70 on average) between 2023 and 2024. These results were in line with Fst estimates, which were 0.015 between France and China, 0.006 between France and Thailand, and 0.020 between China and Thailand, indicating that the populations in the three countries are genetically close. Genetic correlations among the countries ranged from 0.70 to 0.79 for AGE, 0.95 to 0.98 for NFT, 0.53 to 0.83 for BW, 0.81 to 0.97 for NBA, and 0.77 for BFT. Therefore, there was no evidence of G × E interaction except for BW between France and China (0.67), and BW between China and Thailand (0.53). In conclusion, we found high genetic connectedness across countries, demonstrating that animals from different countries share sufficient genetic links to enable accurate and fair across-country genetic evaluations and comparison of EBVs. No biologically significant G × E interaction was detected (except for BW), which suggests that there is no substantial reranking of animals between the countries. Therefore, a single breeding program across these countries is appropriate and effective.