Identification of genes associated with milk productivity of cows of simmental and red steppe breeds of Kazakhstan

The genetic structure of the Simmental and Red Steppe breeds at the CSN3, BLG, and PIT-1 loci is characterized by a high frequency of heterozygotes (at the level of 45–50 %). The proportion of homozygotes varies in breeds. Thus, the frequency of CSN3 AA and CSN3 BB in simmentals is 27 and 24 %, and in Red Steppe breed – 34.2 and 16.6 %. According to the BLG gene, the frequencies of homozygotes in the two breeds are relatively equally distributed – 12 % (BLG AA ) and 37 % (BLG BB ). In contrast to the equal ratio of allelic variants of the CSN3 gene, the frequency of the BLG B allele is 1.8 times higher than the alternative allele (p < 0.01). Interbreed differences in the frequency of PIT-1 AA and PIT-1 BB genotypes (p < 0.05) have been established. The frequency of homozygotes in Simmentals is 23 % (PIT-1 AA ) and 30 % (PIT-1 BB ), while in the Red Steppe breed it is 9.2 % and 47.5 %, respectively. The frequency distribution of alleles in simmentals is relatively equal, while PIT-1 B prevails in the red steppe (70 % versus 30 %). In Simmental cows, it was found that the homozygous CSN3 B genotype has a positive effect (p < 0.05) on increasing milk yield, milk protein and fat in milk compared with other genotypes. There are no statistically significant differences between animals of different genotypes in the CSN3 gene in red steppe cows and the ΒLG gene in both breeds. The degree and direction of the relationship between indicators of milk productivity, hematological and biochemical parameters of blood in animals of the Simmental and Red Steppe breeds, taking into account their genotypic affiliation, which can be used in assessing the functional variability of traits, have been established.