Introduction. The main direction of increasing the productivity of milk is to increase the proportion of heredity of the Holstein breed in the genotype of cows. Industrial breeds in Ukraine are improving due to the increase in the Holstein inheritance in the genotype of cows. The "holsteinization" of the most widespread domestic Black-and-White diary breed is intensively conducted. Currently, the percentage of heredity from Holstein is 90% or more. The negative effect of "holsteinization" appeared in reducing the resistance of animals to diseases that led to the spread of necrobacterial pathology. The control of the spread of necrobacteriosis can be based on genetic markers. Important markers can be the allele of the BoLA-DRB3.2 gene responsible for the formation of adaptive immunity. Due to the ambiguity of the results of "holsteinization", the following tasks were solved: To study the genetic structure of the herd for the BoLA-DRB3.2 gene at the beginning of the "holsteinization" and now. To compare the detected genetic structures with the alleles spectrum of North American Holstein and identify quantitative and qualitative changes in the structure of the herd genotype. To determine the effect of "holsteinization" on the dynamics of milk production and the state of morbidity by necrobacteriosis. Materials and methods of research. Comparison of alleles of population of the Ukrainian Black-Pied Dairy (UBPD) breed and Holstein breed was conducted to detect the consequences of "holsteinization" on milk yield and incidence of necrobacteriosis. The data of the allelic polymorphism of the BoLA-DRB3.2 gene of the UBPD10 (2010, n = 162), UBPD15 (2015, n = 114) and two Holstein populations of the USA and Canada were collected. The allelic spectrum was determined by the PCR-RFLP method. The amplification of the BoLA-DRB3.2 gene was performed using 2-step PCR with the use of primers HLO-30, HLO-31 and HLO-32 and allele-specific PCR. Restriction analysis was performed with endonuclease RsaI, HaeIII, BstYI (XhoII). Restriction fragments were separated by electrophoresis in 4% agarose gel. Counting of allele frequencies was performed taking into account the number of homozygotes and heterozygotes found for the corresponding alleles. To determine the phylogenetic relationships between the populations of the studied herds, genetic distance and genetic similarity were determined by the M. Nei method. Individual dairy productivity of cows was estimated for all lactation (regardless of its duration). Average milk yields were determined as the total volume of milk produced divided by the number of dairy cows. Results and discussion. The breeding measures carried out led to the accumulation of alleles characteristic of the Holstein breed. For Holstein, there are eight alleles with a frequency of more than 4%. It is alleles *03, *07, *08, *11, *16, *22, *23, *24. A high degree of consolidation of weighty alleles can be outlined. In total they occupy 84,6% of allele spectrum of the population. Consolidation of such alleles in the herd of the Ukrainian Black-and-White diary breed is much lower - only 52.2%, although it increased by 6.2% over 5 years. Alleles *10, *13 and *28 are "weighty" for the Ukrainian Black-and-White diary breed, but they are almost non-existent in Holsteins. The genetic similarity of the herd UBPD15 and Holstein increased by ΔI = 0,085, and the genetic distance between the herds of the UBPD increased by ΔD = 0,085 for 5 years. The comparison of the allele spectrum of Holstein and the Ukrainian Black-and-White diary breed shows both the accumulation and the elimination of alleles associated with high productivity. The largest consolidation is typical for alleles *24 (+ 6.75%) and *16 (+ 4.65%). The frequency of "milk" alleles *22 and *08 decreased, respectively, by 4.14 and 1.27%. Alleys, which cause low milk productivity, have the following dynamics: * 23 + 2.53%, *11 – 0.67 and *28 – 0.26. The accumulation of alleles *16 and *23 (7.18%) was found that are associated with predisposition to necrobacteriosis and elimination of *03 and *22 alleles (4.75%) that influence on this disease. Conclusions. It is determined that the role of alleles characteristic for Holstein is increasing in the the Ukrainian Black-and-White diary herd. Breeding measures for holsteinization are conducted in the right direction. There is accumulation of alleles associated with high milk productivity and predisposition to necrobacteriosis. It positively affects the growth of milk production and negatively affects the incidence of necrobacteriosis.
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