Identification of polymorphisms of the BoLA-DRB3.2 locus in samples of black-and-white cattle from different time periods

The leukemia virus causes persistent lymphocytosis in cattle, resulting to significant economic losses. There are genetic mechanisms of resistance to the development of the disease. It is important to monitor cattle herds for carriage of the leukemia virus and genotype animals to identify alleles associated with resistance to leukemia development. The aim of the work is to assess changes in allele frequencies of the BoLA-DRB3.2 locus in the blackand-white breed of cattle due to breeding work. Samples of biological material from modern animals of the black-and-white breed (BLWT_MOD, n = 10), as well as archival samples of animals used in breeding work in the late 70s — early 80s of the twentieth century (BLWT_OLD, n = 10) were studied. Based on the complete sequences of the 2nd exon, the allele polymorphism of the BoLA-DRB3.2 locus was determined. A decrease in allelic diversity was observed: 14 unique alleles were identified in the modern population, and 17 in the archived population. As a result of the breeding work in the modern population, the proportion of resistant alleles in the modern population increased by 33.33%, and the proportion of sensitive alleles by 50% compared to the archived one. The proportion of neutral alleles or alleles with unknown status in the modern population has decreased slightly (by 23.08%). The enrichment of the modern population of black-and-white cattle with alleles associated with sensitivity to leukemia may be associated both with their introduction into the gene pool as a result of crossbreeding with Holstein bulls, and with the breeding work aimed at increasing milk productivity. Significant economic losses as a result of low productive longevity of leukemia-sensitive animals require adjustment of the breeding work taking into account the allelic status.