Molecular genetic markers for blood serum insulin-like growth factor I concentration and growth traits in beef cattle

This study was designed to identify genetic markers associated with blood-serum insulin-like growth factor I (IGF-I) concentration and growth traits in beef cattle. The experimental animals were purebred Angus calves divergently selected for high or low blood serum IGF-I concentration. The promoter and coding regions of the IGF-I, growth hormone (GH), and growth hormone receptor (GHR) genes were examined for polymorphisms using SSCP or DGGE methods, and were sequenced. PCR-RFLP procedures were developed to determine the genotypes of the calves for the polymorphisms. The IGF-I concentration and growth traits were analyzed using animal models with an additive genetic relationship matrix. A two-allelic polymorphism was identified in the promoter region of the bovine IGF-I gene, and was determined to be a T to C transition. Marker genotypes were determined for 760 Angus calves born in the spring and fall from 1993 to 1997. In addition, three new single nucleotide polymorphisms (SNPs) were identified in the promoter region of the GH gene. Genotypes for the first two SNPs and a polymorphism at codon 127 were determined for 468 Angus calves born in the spring and fall from 1995 to 1997. One SNP in the promoter region of the GHR gene and four SNPs in the 10th exon of the GHR gene also were identified. Marker genotypes were determined for 470 Angus calves born in the spring and fall from 1995 to 1997. The analysis showed that the polymorphism at the IGF-I locus is a potential genetic marker for postweaning growth, especially growth during the first 20 d after weaning. The polymorphisms in the GHR gene were significantly associated with blood serum IGF-I concentration. The polymorphisms in the promoter region of the GH gene were associated both with blood serum IGF-I concentration and with postweaning growth traits. Marker associated effects may differ from population to population. Therefore, the associations of these genetic markers with serum IGF-I concentration and growth traits need to be verified in other populations.