We assessed the interaction of GH gene polymorphisms (AA, AB and BB genotypes) with body weight and measures of endocrine function in Japanese black calves at 10 months of age. The average body weight for the BB genotype (281 ± 5 kg) was significantly lower (P = 0.0017, ANOVA) than those for the AA (324 ± 9 kg) and AB (317 ± 7 kg) genotypes. Plasma concentrations of insulin and IGF-I were greater for the AA genotype than for the AB genotype, and AB and BB genotypes, respectively. There were significant differences in the triglyceride and cholesterol concentrations among the GH genotypes. The area under the basal GH concentration was significantly greater (P = 0.0314) for the AA genotype than for the two other genotypes. The incremental area over the basal GH concentrations in response to intravenous GHRH injection (0.4 μg/kg BW) was significantly smaller (P = 0.0005) for the BB genotype than for the two other genotypes. In addition, linear regression analysis between GH incremental area induced by GHRH and body weight demonstrated that there was a positive linear correlation (r = 0.6496, P < 0.002) for incremental areas less than 600 ng min/ml, but a negative correlation (r = 0.6473, P < 0.05) for incremental areas over 600 ng min/ml. These findings indicate that the GH genotypes of the animals could be associated with difference in the GH response in Japanese black cattle at 10 months of age. We also observed a relationship between genotype and animal performances, but other studies on more animals in different conditions must be realized to make a definite conclusion.
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