Features of dairy productivity of cows depending on age and selection

Relevance. An analysis of the structure of the breeding stock, including the selection method for breeding Holstein cattle, revealed a large number of cows obtained as a result of inbreeding, the degree of which will increase over time. Methods. The object of the study is repair heifers and cows born in 2018, divided into groups according to the type of selection – heterogeneous selection (outbreeding) and homogeneous selection (moderate and long–term inbreeding). The material and data for comparison were the database of the IAC “SELEX-Dairy Cattle”, the results of our own research. Milk yield for 305 days of lactation was taken into account according to control milks, MJ and MDB in milk. Results. The majority of cows were obtained as a result of the use of remote inbreeding — more than 65.0%. Cows obtained by heterogeneous (unrelated) selection turned out to be only 12.4%. Cows with the highest productivity rates were found in the second lactation — 10484±135.86 kg (13.8%), which was 1450 kg more than in the first heifers and 169 kg (1.6%) in the third lactation. Further, there was a slight decrease in milk yield by 16 kg and 301 kg, respectively, or by 0.15% and 2.9%. Cows obtained as a result of a moderate degree of inbred had the best indicators. They outperformed animals from other groups by 559 kg, or 5.46% (outbred) and by 268 kg, or 2.62% (distant inbreeding). In animals obtained as a result of outbred selection and moderate inbreeding, there is a gradual decrease in the ratio from the maximum for the first to the minimum for the last (fourth) lactation. In cows with distant inbreeding, the ratio of fat and protein in milk decreased sharply after the second lactation.