Dairy cattle breeding employs both heterogeneous and homogeneous selection. The impact of the inbreeding level on productive traits and length of the productive life of cows is assessed. It is found that despite an insignificant increase in milk yield of inbred animals (by 93–378 kg, depending on the inbreeding level, and on average by 73 kg per the inbred animals group), their milk quality, namely mass content of fat and protein, is found to decrease, and the live weight is revealed to significantly increase (P⩽0.05). Herd cows are superior in terms of the requirements of the standard for black-motley breed by 2500–2947 kg in groups (on average by 2624 kg) in milk yield and by 0.31% in the fat content in milk. For the Holstein breed, these results are insignificantly lower and amount to 1500–1924 kg (an average of 1624 kg) for milk yield. Inbred cows with moderate levels of inbreeding and outbred animals yielded the greatest amount of milk and nutrients due to an increased length of productive life. With age, milk production of cows virtually does not change and remains at a sufficiently high level. Closely related crossbreeding and an increased pedigree index in the Holstein breed increase the milk yield and the length of productive life by 0.2–0.4 lactation. Inbred cows with a moderate degree of inbreeding remain superior to outbred cows in life-long productivity.

In the Sverdlovsk region Holsteinized Black Pied cattle of the Ural type are bred which are represented by large, highly productive animals with a high genetic potential for productivity. Great importance is attached to the rearing replacement calves. The aim of the study was to study the dynamics of the live weight of replacement heifers from different seed bulls during rearing and its dependency on the age of the first insemination. The highest average daily weight gains were in the dairy period of heifers development, they ranged from 989 g for the daughters of the bull Thunderline to 1054 g for their peers from the bull Maximum. There were also high average daily gains during this period when rearing heifers from the bull Renigend. In the second period of rearing from 6 to 10 months of age there was a decrease in the average daily weight gain in all groups. Heifers from different seed bulls reach the required live weight for the first insemination at different ages. Maximum’s daughters, which had the weight of 399.4 kg at the age of 12.9 months. reached the required live weight most quickly. Their peers from other seed bulls reached the aforementioned live weight only at the age of 13.7 months.