Polymorphisms in the 3′UTR of the TGF-β1 gene associated with litter size in Ujimqin and Sonid sheep

Reproductive characteristics like ovulation frequency and litter number significantly impact the sheep industry. Transforming growth factor beta 1 (<i>TGF-β1</i>) functions as a multifunctional regulator of key reproductive processes, plays a pivotal role in mammalian ovarian development. However, research on the role of the <i>TGF-β1</i> gene in the reproduction of Ujimqin and Sonid sheep breeds remains scarce. Thus, this study identified 11 new variants of the <i>TGF-β1</i> gene in these breeds by direct sequencing. In these 11 variants, the Sonid-linkage disequilibrium (LD)1 and Ujimqin-LD1 (comprising the g.50044287 G > A and g.50044526 G > C polymorphisms) in the 3' untranslated region of the <i>TGF-β1</i> gene were significantly associated with litter size in Sonid and Ujimqin ewes (<i>p</i> < 0.01, <i>p</i> < 0.05, respectively), and the single g.50044837 C > T polymorphism in the 3'UTR was also associated with litter size in Sonid sheep (<i>p</i> < 0.01) through association analyses. These findings may provide potential genetic markers for improving prolificacy in sheep.