The research was conducted in the laboratory of molecular genetic expertise in 2018 and 2019 within the framework of the state assignment on the topic "Development of genetic-selection and theoretical foundations for the conservation and effective use of the gene pool of cattle in the Ural region with the use of modern biotechnologies". The object of the study is the cattle of Holsteinized black-and-white breed. The main task is to analyze the degree of influence of the somatotropin (GH) gene polymorphism on lactation performance indicators. In the course of the study, DNA from 270 cows was isolated, the polymorphism of the somatotropin gene was determined based on the obtained data, and the relationship between different genotypes and indicators of live weight, milk yield, protein mass fraction and fat mass fraction in milk was established. The results were biometrically processed using IBM SPSS Statistics 23 software program. It was revealed that LL is the main genotype of the GH gene among the representatives of the Holsteinized black-and-white breed (frequency of occurrence 77.0%). The proportion of LV and VV genotypes in the population is 21.9 and 1.1%, respectively. During the observation period, cows carrying the LL genotype showed higher milk yields in the first and third lactations. The difference with their peers was 202-2334 kg (p ≤ 0.05). A tendency towards increased protein content in milk was recorded in animals with the VV genotype. In the first lactation, the difference with LL and LV genotype carriers was 0.03 and 0.06%, respectively. In the third lactation, individuals with the VV genotype surpassed their female counterparts in protein content by 0.07 and 0.12%, respectively.

Currently, marker genes are often used in dairy cattle breeding. Scientists are studying the relationship of gene polymorphism with such economically useful traits as milk productivity, productive longevity, growth, development, etc. The short period of the economic use of cows and the late intake of live weight necessary for insemination cause economic losses to agricultural organizations. The goal of the research was to study the relationship of the polymorphism of the somatotropin gene with live weight during the first insemination and productive longevity of cows. The study was conducted in the Sverdlovsk region on cattle of Holstein Black-Motley breed in 2018–2019. Two samples were formed: heifers and retired cows genotyped by the somatotropin gene. In animals, LV-somatotropin gene polymorphism was determined. The determination of polymorphism included the following steps: DNA isolation, polymerase chain reaction (PCR), restriction enzyme production, restriction products run on an agarose gel, visualization using a transilluminator. The research results were processed using IBM SPSS Statistics 23 software,and the reliability criterion was analyzed. LV-polymorphism is represented by three genotypes: LL,LV and VV. The authors studied the frequency of genotypes in the population of holsteinized cattle. It was revealed that the LL genotype is widely represented in the population – 77.2%, animals with the LV genotype are found more rarely – 22.2%. The VV genotype is extremely rare in the population – 0.6%. It was also revealed that the L allele is a common population allele – 88.3%. In the course of studying the relationship of LV polymorphism with live weight during the first insemination, it was found that animals with the LL genotype grow faster and reach the live weight necessary for fruitful insemination earlier. At the same age, heifers with the LV genotype had a mass of 400 kg, with those with the LL genotype – 9 kg more at p ≤ 0.01. When studying the effect of somatotropin gene genotypes on productive longevity, it was found that cows with the LV genotype have a longer economic use. The difference with peers with the LL genotype was 0.5 lactations at p ≤ 0.05. As a result of the studies, it can be concluded that the LL and LV genotypes are the desired option for the holsteinized cattle population. The LL genotype is associated with growth and development, and LV – with productive longevity.

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