Association Analysis between a Polymorphism in the 5' Regulatory Region of the IL-6 Gene and Litter Size in Pigs

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.