[Study of the association between alleles of the growth hormone receptor and prolactin receptor genes of bulls and the milk productivity of their daughters].

A substitution of thyrosine for phenylalanine (F297Y) in the transmembrane domain of the growth hormone receptor (GHR) was tested for significance for breeding evaluation of bulls of the holstenized Black-and-White breed. The breeding value was estimated by the method of daughter yield deviation to contemporaries with modification. The frequency of genotype FF in the bulls examined was 0.37, lower than in Holstein bulls (0.67). The F297Y substitution exerted the greatest effect on the milk fat content (1.5 sigma) and milk yield (0.8 sigma) and a lower effect on the milk fat yield (0.6 sigma), milk protein yield (0.5 sigma), and milk protein content (0.6 sigma). The GHR4.2 single nucleotide substitution (SNP) in the promoter of the GHR gene did not affect the milk production traits. A substitution of asparagine for serine (S18N) in the transmembrane domain of the prolactin receptor (PRLR) was also examined, but it did not significantly affect the milk production parameters. The results are discussed in the context of the hypothesis that multiplicity of causal mutations of a particular gene is common and should be taken into account in the genetics of quantitative traits.