Genetic structure of holstein first-calf heifer population based on polymorphism of milk protein genes CSN2, CSN3, and BLG

The article presents the results of a study on the genetic structure of a population of Holstein firstcalf heifers based on the polymorphism of milk protein genes CSN2 (β-casein), CSN3 (κ-casein), and BLG (β-lactoglobulin). The study was conducted on a herd of 947 animals kept at the «Krasnodarskoe » educational and experimental farm in Krasnodar Krai. The frequencies of individual genotypes and alleles, as well as combined genotypic combinations across the three loci, were analyzed. It was established that the most common genotypes in the population are CSN3 AB, CSN2 AA, and BLG AB. The CSN2 gene was characterized by near-complete dominance of allele A (frequency 0,986), while CSN3 showed high allelic variability (A – 0,470; B – 0,402; E – 0,128). In the BLG locus, a balanced distribution of alleles A and B was identified (57,2% and 42,8%, respectively). The findings made it possible to draw conclusions about the intensity of selection pressure on the studied loci and the potential for using genotypic information in genetic improvement programs for dairy cattle. The paper studies the conformity of genotype distribution of three genes (CSN3, CSN2 and BLG) to the Hardy-Weinberg law using the chi-square method. The results show that the CSN3 gene is in equilibrium, while intense selection is observed for CSN2, as evidenced by the high fixation coefficient. The BLG gene is also in equilibrium, but high heterozygosity may indicate adaptive strategies of the population. The results can be applied in the development of highly productive herds with optimal milk processing qualities.