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.

Lambing interval is an indicator of reproductive efficiency in ewes. This study characterized population-level lambing interval patterns in Hu and Tan sheep and evaluated three previously reported candidate SNPs in ADAMTSL1, CD226, and PAPPA. Among 256 genotyped Hu ewes and 94 genotyped Tan ewes, 244 and 92 ewes, respectively, had at least two valid lambing dates. After applying a unified quality-control range of 180–450 days, 711 intervals from 230 Hu ewes and 219 intervals from 82 Tan ewes were retained. The raw mean lambing intervals were 277.81 ± 27.56 days in Hu sheep and 368.81 ± 22.51 days in Tan sheep. After adjustment for parity, year, season, preceding litter size, and repeated ewe records, Tan sheep had an 80.99-day longer interval than Hu sheep (95% CI: 75.34–86.64 days; p = 3.17 × 10⁻¹²⁶). This difference remained significant across all parity groups. None of the three candidate SNPs was significantly associated with adjusted lambing interval after false-discovery-rate correction. Analyses of within-ewe interval variability also yielded no supported associations, although CD226 showed a weak, non-significant tendency toward lower variability in Hu sheep. These findings demonstrate a marked population-level difference in reproductive timing but do not support the immediate use of the tested SNPs as markers for lambing interval or within-ewe interval variability.