Effect of Milk Productivity and Age of Cows of Black-Motley Breed on Homeostasis
Two experiments have been carried out in the instructional farm «Kokino» (the Bryansk region). The first experiment studied the effect of age (group 1 - three-year-old animals, group 2 - seven-year-old ones), the second experiment tried to find out the influence of milk productivity level on a set of indicators characterizing the homeostasis of black-motley cows (group 1 - 13 liters per day, group 2 - 20 liters per day). It has been established that the value of indicators characterizing the homeostasis of black-motley cows depends to a larger extent on the age than on the level of milk productivity. Compared to three-year-old animals, seven-year-old cows had a lower level of metabolism, as indirectly indicated by a higher content of basophils in blood (66.67%), the reduced level of immune protection, as evidenced by a lower content of blood lymphocytes (by 36.39%), the calcium-phosphorus ratio distortion (1.69), and the marked catabolic processes, as reliably evidenced by a higher urea content in blood (26.59%). Moreover the pronounced tendency for higher content of total bilirubin in the blood of seven-year-old cows (56.86%) may indicate cholestasis. The cows of black-motley breed with milk productivity of 13 liters and 20 liters per day had no significant difference concerning a number of homeostasis indicators, but for a lower level of basophils in the blood of more high-productive cows, the fact indirectly indicating a higher level of the animals’ metabolism. At the same time the tendency to higher content of protein (by 5.06%) and of glucose (2.98%) in the blood serum of the more highly productive cows, which may be due to the necessity of their use for more intensive milk synthesis. Besides the highly productive animals had liver dysfunction, as indicated by the tendency of the increased direct bilirubin in their blood.