Polymorphisms of IGF-IR gene and their association with economic traits in two indigenous Chinese dairy goat breeds

The insulin like growth factor 1 receptor (IGF-IR) plays an important role in regulating growth and development. To investigate the effects of IGF-IR polymorphisms on the economic traits of dairy goats, polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) and DNA sequencing methods were used to screen single nucleotide polymorphisms (SNPs) within 9 IGF-IR fragments in Xinong Saanen dairy goat (XS, n = 268) and Guanzhong dairy goat (GZ, n = 440). Consequently, two SNPs, including NC_007319: g.26688 C > T (Leu 608 Leu) and NC_007319: g.28273 T > C within exon 9 and intron 10 were identified in R8 and R9 loci, respectively. At R8 locus, three genotypes were found, including CC, CT and TT, with genotypic frequencies of 0.11, 0.65 and, 0.24 respectively in XS goats, and 0.13, 0.78 and 0.09 in GZ goats; three genotypes which are C1C1, C1T1 and T1T1 were also found in R9 locus, with the genotypic frequencies of 0.48, 0.20 and 0.32 in XS goats, and 0.43, 0.22 and 0.35 in GZ goats, respectively. Based on x(2) test, both XS and GZ populations were deviated from Hardy-Weinberg equilibrium at above two loci. The association analysis revealed that XS goats with CC genotype at R8 locus had heavier milk density than the CT ones (P < 0.05). At R9 locus, the body height of GZ goats with C1C1 and T1T1 genotypes was significantly higher than those with C1T1 genotype (P < 0.01 or P < 0.05). The individuals of GZ goat with C1C1 genotype had longer body length than those with T1T1 genotype (P < 0.05). The individuals of XS with T1T1 and C1T1 genotypes had higher body height than those with C1C1 genotype (P < 0.05). This study can provide theoretical and practical significances to improve the milk production traits and promote the growth and development in two Chinese indigenous dairy goat breeds.