Influence of the age of cows on the dynamics of dairy efficiency depending on a breeding line

The article suggests that one of the most widespread dairy breeds in the world is the Holstein breed; and the black-mottled breed in the Russian Federation. This breed has been improving during the past four decades by interbreeding it with the best one, the Holstein breed. A large set of the Holsteinized black-mottled livestock of the high thoroughbred cows of the Holstein breed has been produced. The aim of the work is to study the effect of age on the dynamics of dairy efficiency of the Holsteinized cows depending on the breeding line. At present, the dairy herd of the farm actually consists of cows of three breeding lines, Reflection Sovering 198998, Vis Back Ideal 1013415, Montvik Chieftain 95679. The rest breeds are not developing due to the absence of breeding valuable breeding bulls. It was found that the Reflection Sovering breeding line 198998 has that the highest milk yield during the sixth lactation, and then there is a decrease in milk yield. The article considers that the milk yield changes with age, starting from the first lactation, increasing during the second lactation and then it is gradually decreasing in productivity to the fifth one. The regularity of the increase in milk yield of mature cows during the third and fourth lactation is not confirmed of the dairy cows of this breeding line. It can be explained by the intensity of herb replacement, when it accumulates a significant amount of nutrients in the body. That is why, they can be used during the first and the second lactations without restoring nutrients in further. Dairy cows of the Vis Back Ideal 1013415 breeding line have a gradual increase in milk yield, starting from the first to the fourth lactation, by 52, 292, 300 kg or by 0.5; 2.8% and 2.8%, respectively. Further, there is a decrease in dairy efficiency. At reaching physiological maturity they have a natural increase in dairy efficiency. The same tendency is observed with cows of the Montvik Chieftein 95679 breeding line.