Е. Ю. Цис High productivity and longevity of animals are the key challenges in modern dairy farming. In addition to high milk yields, first-calf heifers also have to increase their body weight. Due to their physiological characteristics, they are unable to consume large amounts of bulky forage to provide energy and nutrients for potential productivity. One of the ways to solve this problem is to increase the feeding level of first-calf heifers at the expense of concentrates. The assessment of the relationship between the level of feeding and the level of productivity and health of the animal was carried out by studying metabolic processes using biochemical markers of blood serum. The studies were carried out in the Moscow region for 150 days on 36 first-calf heifers, which were divided into three groups of 12 cows each according to the group-analogue principle. The control group received a ration balanced according to detailed norms for annual productivity of 8 to 9 thousand kilograms of milk per lactation. The second experimental group received a ration with increased content of metabolizable energy by 7.8% and crude protein by 8.2% of the requirement, the third group – by 15.1% and 16.4%, respectively, due to additional feeding of a targeted protein- vitamin-mineral concentrate. The researchers found that increasing the feeding level allowed to increase the live weight of first-calf heifers by 5.6% and 6.8% and the average daily milk yield by 6.4% and 9.6% in comparison with the control, and did not have a negative effect on the character of metabolism. All indicators of protein, lipid, carbohydrate and mineral metabolism were within reference values. The content of the albumin fraction in the blood serum of cows in the experimental groups was 39.7% and 39.5% of the content of total protein, while in the control group it was 36%. A significant increase in the content of the albumin fraction, by 5.12% (p=0.04) in the 2nd experimental group and by 7.24% (p=0.01) in the 3rd experimental group, with a simultaneous decrease in the content of total protein, characterizes a higher intensity of biosynthetic processes in the body associated with increased milk formation. Indicators of mineral metabolism were also within the physiological norm. The increase in magnesium content in cows of the 3rd experimental group is associated with an increase in its level in the diet of first-calf heifers. The increase in alkaline phosphatase activity indicates an increase in the functional activity of the liver, which is also associated with milk formation.
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