The level of bactericidal activity of blood serum in lactating cows of different genetic origin

The studies were conducted on lactating cows of a black-and-white Holstein breed of different genetic origin, obtained from bulls of line Reflection Sovering (group 1) and Vis Ideal (group 2). 10 cow analogues were selected from each bull line. The animals were kept and raised in the same conditions and received a similar diet. The level of milk productivity in both groups was almost the same and amounted to about 17,000 kg per lactation. Once a month, before morning feeding, blood was taken from the experimental cows from the subcostal vein. The obtained data were subjected to biometric processing. The bactericidal and lysozyme activity of blood serum was determined in the obtained blood samples according to a generally accepted method. The indicator of bactericidal activity of blood serum (BASC) decreased at the peak of lactation and increased towards its end. So, at the 2nd month of lactation (peak lactation), there was a decrease in the bactericidal activity of blood serum in group 1 by 6.8%, where the indicator was 63.4 ± 2.9%, and in group 2 by 10%, where BASC was 60.0 ± 2.6%. Subsequently, during lactation, an increase in the level of bactericidal activity of blood serum was noted in both groups of animals studied. The highest BASC value was reached at the 10th month of lactation, where it was 83.1 ± 3.0% and 80.4 ± 3.4% in groups 1 and 2, respectively. The BASC level 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 differences between the experimental groups were statistically unreliable (P>0.05). A negative correlation was established between BASC indicators and average daily milk yields in the studied groups, which amounted to r= -0.81 in bull line cows, and r= -0.92 in bull line cows.