Screening of Candidate SNPs Potentially Associated with Multi-Parity Litter Size and Litter Weight in Hu Sheep

Multi-parity records improve ewe evaluation but require long-term follow-up. This study compared litter size, litter weight, and lambing type across four parities in 256 Hu sheep and 90 Tan sheep and evaluated six candidate SNPs in Hu sheep. The SNPs were confirmed by PCR and Sanger sequencing and genotyped using PARMS; repeated records were analyzed with mixed-effects models. The Hu sheep population showed higher litter weight and multiple-birth proportions than the Tan sheep population, together with a higher mean litter size. Analysis of 822 records from 256 Hu ewes showed that both traits increased from the first to the third parity and then remained stable; the same pattern occurred in 156 ewes with complete records. After BH-FDR correction, BMPR1B rs418841713 and TSHR rs406686139 were significantly associated with both traits. Association directions were unchanged when analyses were restricted to complete records, low-frequency genotypes were recoded, or lambing year was included. In an independent population, combined-genotype differences were nonsignificant, although GGCG had the numerically highest total litter size. An exploratory model indicated that first-parity litter size and both genotypes provided information on subsequent litter weight, but predictive performance was limited. These findings support further validation of BMPR1B and TSHR in Hu sheep.