Stimulated growth hormone (GH) release in Friesian cattle with respect to GH genotypes

The effects of bovine growth hormone (GH) polymorphism at the amino acid position 127 (substitution of leucine to valine) on milk and meat production traits have been reported; however, the physiological background of this influence has not yet been recognised. The aims of this study were to estimate allele frequencies of the growth hormone gene in a population sample of Friesian cattle, and to characterise the TRH-induced GH release with respect to GH genotypes. The analysis covered data on 214 Polish Friesians, aged 11 months, used to identify GH genotypes by the PCR-RFLP technique. Frequencies of leucine (Leu) and valine (Val) alleles were 0.69 and 0.31, respectively. The GH release was analysed after thyrotropin releasing hormone (TRH) stimulation in blood samples collected over a period of 2.5 h. There was a lack of significant difference in the overall characteristics of GH release in the blood of Friesian cattle with different GH genotypes (P > 0.05). Nevertheless, the Val/Val homozygotes had higher GH baselines both within heifers and bulls (14.1 +/- 2.8 and 14.6 +/- 2.0 ng.mL-1, respectively) than others. Moreover, males of the Val/Val genotypes showed the highest peak amplitude of GH release (55.5 +/- 8.1 ng.mL-1) in comparison to all other animals. The results presented provide evidence for the lack of difference in stimulated GH release with respect to GH genotypes in dairy cattle.