Genotypic and paratypic factors in the herd of Holstein cattle on the example of a breeding reproducer

In the selection of dairy cattle, great importance is given to population genetic parameters. The studies were carried out in 2021-2022 at the Federal State Budgetary Scientific Institution of the Federal Scientific Center of the WBC of the Oryol Region, in a herd of black-and-white Holsteinized cows, corresponding in terms of genotype and productivity to the standards of the Holstein breed. Feeding was carried out in accordance with physiological norms and needs. The heritability of selection traits was studied, as well as the proportion of genotypic and paratypic variability of selection traits in the herd. It was found that in the herd of cows of V.B. Ideal and R. Sovereign differed significantly in heritability of milk production traits. So, if heritability (h2) for milk yield in the line of V.B. Ideal (n=460) was 0.160, then in the R. Sovereign line (n=220) it was 0.592. With an increase in milk yields up to 6000 kg of milk and above, there was a tendency to increase the genotypic variability of milk yields up to 0.60, there was a tendency to increase the heritability of the amount of milk fat up to 0.44. This may be evidence that purposeful selection has been carried out in the herd over the past 5 years. In general, for the herd, the genotypic variability of milk yield for 305 days of lactation was 183.4 kg, the environmental variability was 516.6 kg of milk. For milk fat content, these indicators were approximately 0.01 and 0.07%, respectively, for protein content in milk - 0.01 and 0.05, respectively, for the live weight of first-calf heifers, genotypic variability was 9.5 kg. This allows for further selection.