GENETIC DIFFERENTIATION OF SYCHEVSKAYA AND RELATED BREEDS BY EAB-LOCUS ALLELES

The article presents the results of immunogenetic monitoring of the cattle of Sychevka breed, analyzes the similarity with the Red-and-White and Holstein breeds, using alleles of the EAB locus of blood groups as genetic markers. The research was conducted in breeding farms for the Sychevka (n=7602 head), Holstein (7689 head) cattle breeds of the Smolensk region from 1980 to 2025. A change in the structure of the allele pool of the Sychevka breed under the influence of the improving Holstein breed with the introduction of new EAB alleles has been established: BO, BOY, BOYD', E'G'', YA', E'G'G'', D'E'F'G'O'G'', GYD', OA', OA'J'K'O'. The coefficient of genetic similarity (R) between cows born in 1980–1985 and in 2015–2020 is 0.58. The similarity with the Holstein breed for 18 identical EAB alleles was 0.55. The most common (4.0 – 16%) animals in both breeds are carriers of 5 marker alleles: GE'/Q', b, Y'/V, E'/G'G'', Q', with a frequency of 0.444 in Sychevka cows and 0.390 in Holstein cows. Animals the breed of Sychevka, compared with the related red-mottled breed, have a lower index of hereditary variability of 69 EAB alleles, 97 in the red–mottled breed, and a higher level of homozygosity – 6.4 versus 3.4. Markers BIQ, BGOYD'E'G'', IYI', OI'Q', specific for Sychevka cattle have not been identified in animals of the Red-and-White breed. The B, BOYA'E'G'P'Q'G'', A'I'' alleles, characteristic of the Red-and-White breed in the breed of Sychevka animal population have not been established. The coefficient of genetic similarity (R) between the breeds is 0.63 and confirms their family relations. The obtained research results can be used in breeding of the cattle of Sychevka breed to increase productivity and preserve it’s the gene pool.