Abstract
The influence of age and body weight of replacement heifers and bullocks of the Kazakh white-headed meat breed on the protein composition of blood has been studied. After weaning, under the same conditions of husbandry and feeding, the heifers reached a weight exceeding the standard of class I by the age of 15-18 months. At the age of 18 months, the total protein content in the blood increased by 6.32% compared to 8-month-old bullocks. It has been established that proteins play an important role in growth, reflecting the genetic potential of productivity. Changes in the protein spectrum occurred with an increase in body weight. In heifers, the total protein increased with age, remaining within the physiological norm, which indicates sufficient protein supply. In bullocks, the increase in total protein was mainly due to albumins — their level increased by 17.23%, and their share in total protein increased by 12.58%. This was accompanied by a change in the ratio of albumins to globulins (Alb/Gl), reflecting the activation of metabolic processes and an increase in the protein-synthesizing function of hepatocytes. The age of the heifers did not have a significant effect on the level of globulins. Despite the intensive growth, the physiological parameters of the young animals remained within the normal range, which indicates the stability of metabolic processes and an adequate body response to age-related changes.