Beta-lactoglobulin (BLG) gene polymorphism in Ukrainian and foreign cows
Authors:   Institute of Animal Breeding and Genetics named after M. V. Zubets NAAS, 1 Pohrebniaka str, Chubynske village, Boryspil district, Kyiv region, 08321 Ukraine, Mitioglo I. 
Published: February 2022

The aim of the study was to study the polymorphism of the beta-lactoglobulin gene in cows of Ukrainian Red-Spotted dairy cattle and Montbéliarde breeds and animals obtained by crossing the local Ukrainian Red-Spotted dairy cattle with bulls of Montbéliarde breed and its relationship with milk productivity. Blood samples were taken from the cows Ukrainian Red-Spotted dairy cattle and crossbreeds (SE DG “Niva” of the Institute of Animal Breeding and Genetics named after M. V. Zubets) and from cows of Montbéliarde breed (PSP “Zhadkivske”, Chernihiv region). with the end of the first lactation. To study the single nucleotide polymorphism of the beta-latoglobulin (BLG) gene, the PCR-RFLP method with specific primers and restrictases was used. Dairy productivity of cows was determined by control milkings. Statistical processing of the obtained research results was carried out by the methods of biological statistics using the computer program Microsoft Excel. In our groups of cows, we have found three variants of genotypes at the locus of the beta-lactoglobulin gene — homozygous AA and BB and heterozygous AB. In the firstborns of the Montbéliarde breed and crossbreeds of the Ukrainian Red-Spotted dairy cattle with the Montbéliarde bulls, animals with the AB genotype were most common (0.57 and 0.524), in the group of the Ukrainian Red-Spotted dairy cattle — homozygous carriers of the BB genotype with a frequency of 0.433. In individuals of the Ukrainian Red-Spotted dairy breed, the expected heterozygosity (He) exceeds the actual (Ho), which indicates a decrease in heterozygosity in the herd of cows of this breed. In groups of Montbéliarde cows and crossbreeds, the situation is opposite: the actual heterozygosity exceeds the expected one and the fixation index is negative. Analysis of milk productivity of cows of the three studied groups revealed the same trend: cows with the AA genotype for the beta-lactoglobulin gene were dominated by peers with the AA and AB genotypes. The highest hopes for 305 days of the first lactation were found in crossbred cows with genotype AA (6728 kg). The difference in milk yield in crossbreeds with genotypes BB and AB was 311 (5%) and 195 (3%) kg, respectively. The highest indicators of fat content were found in the milk of first-born crossbreeds with the AA genotype, which is 0.1% and 0.75% higher than in the first-born with the AA genotype of Montbéliarde and Ukrainian Red-Spotted dairy cattle, respectively. Among cows with genotype AB, the highest mass fraction of fat was found in crossbreeds — 4.15%. The mass fraction of protein is highest in first-borns with the BB genotype — 3.89%, which was 0.51 higher than in Montbéliarde cows and 0.43% in the Ukrainian Red-Spotted dairy cattle. Thus, the results of molecular genetic analysis of the studied breeds reflect the specificity of the genetic structure at individual loci of quantitative traits, in particular the beta-lactoglobulin gene, which gives grounds to use this pattern to improve breeding work with dairy breeds.