Single Nucleotide Polymorphisms in , , and and the Association with Litter Size in Small-Tail Han Sheep.

, , and have been extensively studied as candidate genes because of their great influence on the reproductive traits of animals. However, little is known about the association between polymorphisms of the , , and genes and litter size in Small-Tail Han sheep. In this study, the expression levels of , , and in HPG (hypothalamic-pituitary-gonadal) axis tissues of polytocous and monotocous Small-Tail Han sheep were analyzed by qPCR. To better understand the effects of four single nucleotide polymorphisms (SNPs) comprising of g.70067210 T > C in , g.25350431 C > T and g.25360220 T > C in , and g.14413132 C > T in , a population genetic analysis was conducted using data obtained from genotyping in 728 sheep from seven breeds. The results indicated that all genes included in this study were differentially expressed in the pituitary and uterus of polytocous and monotocous Small-Tail Han sheep ( < 0.05). The associations of these four SNPs and the mutation with litter size in 384 Small-Tail Han sheep were analyzed, therefore, and it was found that both g.70067210T > C and the mutation were significantly associated with litter size ( < 0.05). The linear regression analysis of the association of multiple markers ( and g.70067210 T > C in ) with litter size indicated that homozygous ewes carrying the BB/TT genotype had larger litter size than any ewes with any other genotype. In conclusion, the SLC5A1 SNPs significantly affect litter size in sheep and are useful as genetic marker for litter size.