ACTIVITY OF INDICATOR ENZYMES IN THE BLOOD OF FIRST-CALF HEIFERS AT DIFFERENT FEEDING LEVELS

The aim of the study is to determine and characterize changes in the main enzyme indicators in the blood serum of first-calf heifers during the peak productivity period at different feeding levels. Objectives: to analyze the enzyme activity in the study groups of animals; to provide a comparative description of the enzyme profile; to evaluate changes in the enzyme activity of the blood serum with different feeding levels. Enzyme activity was determined using generally accepted methods on an automatic biochemical analyzer. Average ALT activity in the blood of animals in the 1st experimental group increased by 25.9 % (p < 0.05) compared to the control group and indicates the intensity of the hormonally controlled gluconeogenesis process. This indicates better physiological adaptation aimed at supporting the activity of the mammary gland of first-calf heifers and is confirmed by higher milk productivity. A decrease in the de Ritis coefficient in first-calf heifers receiving the increased feeding level by 0.27 (p = 0.04) and 0.53, and in the indicator enzyme LDH by 27.55 (p < 0.05) and 17.54 % in the 1st and 2nd experimental groups, respectively, confirms improved protein-synthesizing function of the liver. CPK and lipase activity indicate more efficient energy processes in the body to meet the needs of first-calf heifers in the experimental groups receiving the increased feeding levels and is consistent with milk productivity data and live weight dynamics. Increasing the feeding level by 7–8 % and 14–15 % in first-calf heifers is physiologically more consistent with the body's needs and the intensity of metabolic processes required to realize the genetic potential for milk production in the first half of lactation.