Abstract
Leukemia is one of the most common infectious diseases of cattle in Russia and Kazakhstan. The study is devoted to the analysis of genetic resistance to leukemia by PCR-RFLP in 716 cows (including 75 RID+ cows and 27 cows with hematological changes) and 81 Black Pied and Holstein stud bulls from the Bryansk and Leningrad regions (Russia), Kazakhstan and Belarus. To this end, we have examined the allele frequencies of BoLA-DRB3 gene related to the resistance (R) and susceptibility (S) to leukemia in various groups of animals. Cows from the breeding farms have 44.1-55.2% of S alleles, associated with susceptibility to leukemia, in the commercial farms they make up 20.1-29.4%. The total number of susceptibility S alleles in stud bulls ranges from 49.9% to 70.9%. In cows of all groups, the number of resistance alleles R to leukemia is far greater than in the bulls of all groups. It was shown that the number of S allele carriers is greater among RID+ cows. Analysis of 2 groups of sick cows has revealed that they include no animal units with RR genotype and only by 11-12% of cows with genotype R/S and R/N. The findings suggest the accumulation of S alleles to leukemia under holsteinization of the Black Pied breed, with increased risk of developing leukemia in animals.