GROWTH-HORMONE AND INSULIN-LIKE GROWTH-FACTOR-I CONCENTRATIONS IN BULLS OF VARIOUS GROWTH-HORMONE GENOTYPES

A leucine/valine substitution at amino acid position 127 was identifie d by the polymerase chain reaction and restriction fragment length pol ymorphism in the bovine growth hormone gene. Genotyping was performed in 84 AI bulls of three different breeds, in which plasma concentratio ns of growth hormone (GH) and insulin-like growth factor I (IGF-1) wer e also measured. Gene frequencies of variants L (leucine) und V (valin e) were 0.80/0.20 (Black and White), 0.90/0.10 (Brown), 0.71/0.29 (Sim mental). Hormone concentrations were measured during different physiol ogical conditions (normal feeding, fasting, realimentation) in the maj ority of animals. Generally, genotype LL was associated with higher co ncentrations of GH than LV. This difference was significant in Black a nd White bulls (P < 0.05). In contrast, IGF-1 concentrations were high er in LV than in LL animals. This was most pronounced in mature, reali mented Simmental bulls. We conclude that the various GH alleles influe nce the circulating concentrations of GH and IGF-1.