The aim of this study was to determine the effects of an IL-6 gene polymorphism, discovered in the 5＇ regulatory region, on porcine litter size. An association analysis was performed between the polymorphism and total number born （TNB） and number born alive （NBA） in 421 sows. The polymorphism was at Hpy188I within the 5＇ regulatory region of IL- 6 gene. Three genotypes of AA, AG, and GG were detected in Landrace, and two genotypes, AA and AG, were detected in Yorkshire and Duroc pigs. The A allele was the superior allele in all three breeds, with allele frequencies ranging from 0. 901 to 0.993. The IL-6 genotype was highly significantly associated with TNB and NBA in the third and following parities （ P 〈 0.01 ）, and with total parities （ P 〈 0.05）. In general, the TNB and NBA showed a tendency of GG 〉 AG 〉 AA, indicating that the common allele was the least favorable for litter size. Thus, there is an enormous opportunity to increase litter size if this effect is confirmed in other studies.
Background： Embryonic mortality during the period of implantation strongly affects litter size in pigs. Progesterone receptor（PGR） paracrine signaling has been recognized to play a significant role in embryonic implantation. IHH,NR2F2, BMP2, FKBP4 and HAND2 were proved to involve in PGR paracrine signaling. The objective of this study was to evaluate the expression of IHH, NR2F2, BMP2, FKBP4 and HAND2 in endometrium of pregnant sows and to further investigate these genes＇ effect on litter size in pigs. Real-time PCR, western blot and immunostaining were used to study target genes/proteins expression in endometrium in pigs. RFLP-PCR was used to detect single nucleotide polymorphisms（SNPs） of target genes.Results： The results showed that the m RNA and protein expression levels of IHH, NR2F2 and BMP2 were up-regulated during implantation period（P 〈 0.05 or P 〈 0.01）. All target proteins were mainly observed in luminal epithelium and glandular epithelium. Interestingly, the staining of NR2F2 and HAND2 was also strong in stroma. SNPs detection revealed that there was a-204 C 〉 A mutation in promoter region of NR2F2 gene. Three genotypes were found in Large White, Landrace and Duroc sows. A total of 1847 litter records from 625 sows genotyped at NR2F2 gene were used to analyze the total number born（TNB） and number born alive（NBA）. The study of the effect on litter size suggested that sows with genotype CC tend to have higher litter size.Conclusions： These results showed the expression patterns of genes/proteins involved in PGR paracrine signaling over implantation time. And the candidate gene for litter size was identified from genes involved in this signaling. This study could be a resource for further studies to identify the roles of these genes for embryonic implantation in pigs.
