BMPR1B c.746A>G (p.Gln249Arg) polymorphism is associated with litter size in Tibetan Plateau sheep

The BMPR1B (FecB) c.746A>G (p.Gln249Arg) variant is a major fecundity locus in sheep, but its distribution and association with litter size require population-specific evaluation. We analysed archived genotype and reproductive records from 120 Tibetan Plateau ewes sampled from four flocks in Qinghai Province, China. Genotypes were assigned by PCR-RFLP, and three archived TIFF export panels labelled AA, AG and GG were retained. The genotype frequencies were 0.467 for AA (n = 56), 0.383 for AG (n = 46) and 0.150 for GG (n = 18); the G-allele frequency was 0.342. An exact Hardy-Weinberg test did not detect departure from equilibrium (p = 0.107), although the sample provided limited power for population-genetic inference. In a general linear model treating genotype and flock as categorical fixed effects, genotype (F2,114 = 82.57, p < 0.001) and flock (F3,114 = 4.06, p = 0.0088) were associated with the recorded litter-size outcome. Equal-flock-weight adjusted means were 1.020, 1.759 and 1.750 lambs for AA, AG and GG, respectively. Both G-carrier genotypes differed from AA (Tukey-adjusted p < 0.001), whereas AG and GG did not differ (p = 0.995). Because the GG subgroup was small and parity, lambing season and individual age mapping were unavailable, these findings should be interpreted as exploratory evidence rather than a causal estimate. Independent, prospectively recorded flocks are needed before breeding application.