Population-Level Lambing Interval Patterns and Evaluation of Three Previously Reported Candidate SNPs in Hu and Tan 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.