The level of lysozyme activity of blood serum in lactating cows of the lines of bulls Reflection Sovering and Vis Ideal

The studies were conducted on lactating cows of a black-and-white Holstein breed of different genetic origin, obtained from bulls of the Reflection Sovering line (group 1) and Vis Ideal (group 2). 10 cow analogues were selected from each bull line. The animals were kept in the same conditions and received a similar diet. The level of milk productivity in both groups was similar and ranged from 16759-17002 kg per lactation. Once a month, before morning feeding, blood was taken from their subcostal vein during lactation. The lysozyme activity of blood serum was determined in the obtained samples according to a generally accepted method. The indicator of lysozyme activity of blood serum (LABS) decreased at the peak of lactation and increased towards its end. At the 2nd month (peak of lactation), there was a decrease in LABS in the studied groups, its indicators reached the lowest values for the entire lactation and amounted to 9.1 ± 0.8% and 9.0 ± 0.7%. Further, there was a gradual increase in the level of lysozyme activity of blood serum up to the 6th month, where the values corresponded to 20.3 ± 1.3% and 19.4 ± 1.1% in groups 1 and 2. Then there was a decrease in the level of LABS until the 8th month, where the indicators decreased by 1.2% in group 1 and 0.4% in group 2. Subsequently, the level of lysozyme activity of blood serum increased and reached its highest value at the 10th month of lactation and amounted to 24.3 ± 1.7% in the group of cows of the Reflection Sovering bull line and 23.6 ± 1.8% in the group of cows of the Vis Ideal bull line. The level of LABS was higher in the group of cows of the Reflection Sovering bull line, compared with the group of cows of the Vis Ideal bull line. The difference between the study groups was statistically unreliable (P>0.05). A negative correlation has been established between the level of lysozyme activity of blood serum and the average daily milk yields of cows. So, for cows of the bull line Reflection Sovering, it was r= -0.72, and for cows of the bull line Vis Ideal r= -0.81.