Genetic markers for genes encoding Pit-1, GHRH-receptor, and IGF-II, and their association with growth and carcass traits in beef cattle

Growth and carcass traits are economically important traits and are under the control of multiple genes. Genetic markers on these candidate genes can be useful in marker-assisted selection. Three genes, Pit-1, growth hormone releasing hormone receptor (GHRH-R), and insulin-like growth factor II (IGF-II) genes were analyzed in this research. These three genes are all responsible for animal growth.; The experimental animals used in this study are Angus beef cattle, which were divergently selected for high or low blood serum IGF-I concentration. Single strand conformation polymorphism technique was used to screen for mutations within the amplified segment. Proper restriction enzymes was determined for the polymorphism based on the DNA sequence and used to facilitate genotyping using PCR-RFLP (restriction fragment length polymorphism). The associations of the animal genotypes for each polymorphism with growth and carcass traits were analyzed using General Linear Model (GLM) procedures in SAS.; Five new polymorphisms, Pit1I3H (HinfI), Pit1I3NL ( NlaIII), Pit1I3N (NciI), Pit1I4N (BstNI), and Pit1I5 were found in Pit-1 gene. The previously reported polymorphism in exon 6, Pit1E6H (HinfI), was also studied. For Pit1E6H, a significant relationship was found with birth weight (P = .03), and preweaning gain (P = .01). Significant relationships with Pit1E6H genotypes were also observed on backfat thickness (P = .01) in high IGF-I line, and marbling score (P = .03) in low line.; One NciI polymorphism was detected in exon 6 of the GHRH-R gene in Angus cattle and one AciI polymorphism was detected in the promoter region of the GHRH-R gene in Jersey cattle. Significant relationships were observed between genotypes of the AciI polymorphism and relative value of milk production (P = .05). This polymorphism had an overdominant effect on milk production.; An AciI polymorphism was observed in intron 8 of the IGF-II gene. Significant associations were observed between genotypes and weight gain during the 20-d period between weaning and the beginning of the postweaning test (P = .05), IGF-I concentration at d 28 of the 140-d postweaning test (P = .02), ribeye area (P = .01) and yield grade (P = .03).