A preliminary evaluation towards a breeding value of the Holstein breeding bulls with different genotypes of somatotropin cascade genes is presented: pituitary transcription factor or growth hormone factor (PIT1), prolactin (PRL), somatotropin (GH), somatotropin releasing hormone (GHRH), insulin-like (IGF-1) in the conditions of the Republic of Tatarstan. The research studies the signs (indices) of milk productivity (milk yield and fat in milk) of the closest female ancestors of bulls with different genotypes of somatotropin cascade genes. Studies and analysis have shown that the bulls with the mixed genotypes ABAALLBBAA (10269 kg), AAAALLBBAB (4.13 %) and BBAALLABBB (9402 kg and 4.06 %) had the highest and optimum evaluation by origin, judging by the bulls’ pedigree (geneological) index. The frequency to meet bulls with the desired mixed genotypes was low and amounted to 4.28–5.71 %.

As numerous studies of scientists show, the genotype for prolactin (PRL) and somatotropin (GH) genes of cows affects the milk productivity and the quality of their milk. In this regard, the purpose of this study was to study the milk productivity and qualitative composition of milk in Tatarstan-type cows with different genotypes of prolactin and somatotropin in the conditions of the Republic of Tatarstan. The analysis of the milk productivity of the first heifers of the Tatarstan type with different genotypes according to the loci of the prolactin and somatotropin genes showed that the highest indicators for milk yield, the amount of milk fat and protein had the genotypes PRL/AA, GH/LL and GH/LV compared with analogues of other genotypes.

. Polymorphisms of genes may be useful as genetic markers for additional selection criteria in dairy cattle breeding for economically advantageous traits. The presented study is dedicated to the influence of gene polymorphism, responsible for milk quality and milk productivity was carried out among Holstein cow-heifers in Integrated Agricultural Production Centre “Stud farm named after Lenin” of Atninsky district of the Republic of Tatarstan. DNA samples were isolated from blood samples of 130 cows for genotyping according to gene of growth hormone (GH) by PCR-RFLP analysis method. The genotypes distribution of the somatotropin gene were as follows: LL – 63.8% (83 animals), LV – 30.0% (39 animals), VV – 6.2% (8 animals), the distribution in frequency of occurrence of alleles L - 0.788 and V - 0.212. When considering the gene polymorphism association with the signs of milk production and the qualitative composition of milk showed prominent results cow-heifers with a LL genotype. The identified relationships indicate the possible genetic improvement of the investigated herds using marker-assisted selection.

A preliminary evaluation towards a breeding value of holstinized Black-and-White breed bulls with different genotypes of somatotropin cascade genes is presented: pituitary transcription factor or growth hormone factor (PIT1), prolactin (PRL), somatotropin (GH), somatotropin releasing hormone (GHRH), insulin-like (IGF-1) in the conditions of the Republic of Tatarstan. The research studies the signs (indices) of milk productivity (milk yield and fat in milk) of the closest female an-cestors of bulls with different genotypes of somatotropin cascade genes. Studies and analysis have shown that the highest rating by origin, based on the pedigree index of bull, were bulls with geno-types PIT1/АB, PRL/AA, GH/LL, GHRH/АВ, IGF1/AA (by milk yield) и PIT1/AA, PRL/AB, GH/LV, GHRH/BB, IGF1/BB (by fat content) in comparison with analogues of other genotypes.