Identification of Reproductive Trait-Associated Loci and Candidate Genes in Commercial Pigs via 50K SNP Genotyping and Genome-Wide Association Study.

To unravel the genetic basis of economically critical reproductive traits in swine, we genotyped 839 sows from three commercial breeds (Duroc, Landrace, Yorkshire) using the Porcine Breeding Chip_plus 50K SNP array, and analyzed three key traits: total number born (TNB), number born alive (NBA), and number of healthy piglets (NHP). We integrated principal component analysis (PCA) for population structure, runs of homozygosity (ROH) detection, genome-wide association studies (GWAS), and GO/KEGG enrichment analysis. Phenotypically, Yorkshire sows exhibited superior and persistent reproductive capacity across parities 1-7 (peak TNB: 14.17 ± 2.82 at parity 4 based on N ≥ 3 data), Duroc sows had limited data with only parity 1 available (TNB: 9.44 ± 2.13), and Landrace sows showed moderate to high performance across parities 1-4 and 7, with peak TNB at parity 4 (17.08 ± 4.61). ROH analysis further revealed that short ROH fragments (1-5 Mb) were the most abundant category across breeds, while the majority of detected ROH were under 10 Mb in length. GWAS identified significant SNPs concentrated on chromosomes 1 and 2, and annotated candidate genes including AMH (ovarian reserve), IZUMO4 (embryo implantation), ACSBG2 (steroid synthesis), RFX2 (follicular maturation), and DOT1L (embryonic development). GO/KEGG enrichment highlighted pathways such as "histone methyltransferase activity" and "fatty acid biosynthesis", which are critical for reproductive processes. This study clarifies breed-specific reproductive patterns and identifies key genetic loci/genes for porcine reproductive traits, providing molecular markers and a theoretical basis for improving swine reproductive performance via molecular breeding.