NATURAL RESISTANCE OF HEIFERS OF DIFFERENT BREEDS
Scientific studies were conducted on the Jersey, black-and-white, Montbellard, and red-and-white heifers. At the beginning of pregnancy, the bactericidal activity of blood serum in experimental animals was not the same. The differences between the groups were not statistically significant (P>0.05). In the future, with an increase in the term of pregnancy, the BASC in all experimental heifers gradually increased. By the end of pregnancy at 9 months, there was a decrease in the bactericidal activity of serum in the Jersey breed to 75.4±4.0% in the Montbeliard breed to 77.0±4.8%, in the red-mottled breed to 87.8±4.1%, in the black-mottled breed to 85.6±4.9%. In all periods of pregnancy, the BASQUE was higher in the red-mottled and black-mottled heifers in relation to the compared breeds of Jersey and Montbeliard. The WEASEL, as well as the BASQUE, also had differences in the first month of pregnancy in different breeds. And the same trend continued until the end of pregnancy. At 8 and 9 months of pregnancy, the differences between red-mottled and jersey were statistically significant (P<0.05). In all periods of pregnancy in heifers, a higher WEASEL was observed in red-mottled and black-mottled breeds in relation to the Jersey and Montbeliard breeds.