The study was conducted to determine the frequency of occurrence of the allelic spectrum for the kappa-casein (CSN3) and beta-casein (CSN2) genes to identify the most valuable selection-significant gene complexes of Red Steppe cows with their subsequent consolidation in populations. The object of the study was Red Steppe cows (n = 53) bred in Stavropol krai. Animals with different levels of milk productivity for 305 days of completed lactation were selected by random sampling. The PCR-RFLP method was used to study the polymorphism of the studied genes. The frequency of occurrence of selection-significant homozygous CSN3BB and CSN2A2A2 genotypes was the lowest and amounted to 5.7 and 13.2%, respectively. The highest milk yields were demonstrated by animals carrying the homozygous genotype CSN3AA of the CSN3 gene and the heterozygous CSN2A1A2 of the CSN2 gene—4200.0 and 4192.0 kg of milk, respectively, in 305 days of lactation. The highest fat content was observed in the milk of cows, carrying the heterozygous genotypes CSN3AB and CSN2A1A2, 4.65 and 4.66%, respectively. The proportion of animals, carrying the complex genotypes CSN3BBCSN2A1A2; CSN3ABCSN2A2A2, including three selection-significant alleles (two alleles “B” in the CSN3 gene and one allele “A2” in the CSN2 gene), in the studied sample of Red Steppe cows was 18.87%. The majority of cows (56.60%) were carriers of the complex homozygous genotype CSN3AACSN2A1A1, in which the selection-significant alleles “B” and “A2” were absent. Genotyping of cows by the CSN3 and CSN2 genes complements traditional selection methods based on the assessment of phenotypic traits of animals. The combination of genetic testing and factoring in the productive indicators allows for more accurate prediction of the potential of individual animals and effective management of the selection process.
Gadzhiev et al. (Wed,) studied this question.