Polymorphism of the BoLA-DRB3 gene in the Ukrainian brown breed

The article presents the results of a study of polymorphism in the Ukrainian Brown breed (UB) for the BoLA-DRB3 gene. Experimental data were obtained using the PCR-PCRF method. The genotypes of the animals were determined based on the results of typing blood samples from 30 cows and semen from 10 bulls. Twenty-three alleles and 18 genotypes were identified. The proportion of each of the three most common BoLA-DRB3 alleles, *27, *28 and *50, was 10%. Among other variants, three more stand out with a frequency of more than 5%: *8, *19 and *36. The most frequently detected genotype was BoLA-DRB3.2*32/*54, which was typed in 9 cows (15.0%). The total frequency of consolidating alleles was 50%. Several rare alleles (BoLA-DRB3.2*36, *50, *71 and *98) were detected in the sample, which were rarely found in studies of Major Histocompatibility Complex (MHC) polymorphism in other cattle breeds. A small pool of consolidating alleles and the presence of rare variants with high frequencies indicate the influence of natural selection and regional characteristics of the breed. The observed (0.9) and expected (0.94) heterozygosity indices indicate a high level of genetic variability in the tested animals, which is confirmed by the highest values of the effective number of alleles (16.7) and the efficiency index (0.726). A slight deviation from panmixia detected by Wright’s index proved to be unreliable. The high level of biodiversity of UB is confirmed by the Shannon index (2.97). The presence of specific alleles, established indicators of variability and the Shannon index indicate a high level of genetic differentiation and biodiversity of the breed. Autochthonous populations have unique BoLA-DRB3 variants, which serve as a genetic reserve for future selection and development of the dairy industry, especially in the context of climate change or the emergence of new diseases, as well as a source of genetic diversity for the cattle gene pool.