Comprehensive assessment of cows dairy productivity in the genotypes context

The aim of the study is to investigate the influence of gene polymorphism on milk productivity and pro-duction typicality of Yaroslavl cattle. Objectives: to study the distribution of genotypes and genetic diversity for milk productivity genes in the Yaroslavl cattle population; to evaluate milk productivity of cows depen-ding on the genotype for the following genes: fatty acid synthase (FASN), thyroglobulin 5 (TG5), pituitary transcription factor 1 (Pit 1), diacylglycerol O-acyltransferase 1 (DGAT 1). Research and production expe-riment was conducted in breeding herds of the Yaroslavl Region in the period 2024–2025. The object of the study was purebred first-calf heifers of the Yaroslavl breed (229 heads). The following parameters were analyzed: milk productivity (305-day milk yield, fat and protein content, milk fat and protein content), conformation measurements (2nd–4th month of the first lactation), and biological material (whole blood). The DGAT 1 gene is monomorphic, which is due to directional artificial selection. The FASN gene showed moderate genetic diversity, an effective allele count of 1.68, a Shannon information index of 0.59, an ob-served heterozygosity of 0.48, an expected heterozygosity of 0.40, and a fixation index of -0.18. The PIT1 gene has two alleles, but a lower effective allele count of 1.61 and a Shannon information index of 0.57. A significant deviation of the observed heterozygosity (0.28) from the expected one (0.38) was noted, which was confirmed by a positive fixation index value (0.26). The TG5 gene showed the greatest genetic diversity: effective number of alleles 1.91, Shannon information index 0.67, observed heterozygosity 0.62, expected heterozygosity 0.48, fixation index –0.29. A study of dairy productivity showed that the FASNAG gene genotype has the greatest impact on milk yield. Cows with this variant produced 639 kg more milk than cows with the FASNGG variant (p ≤ 0.001). Cows with the TG5CT genotype yielded 377 kg more milk than cows with the TG5CC variant. Cows with the FASNAG variant had a higher fat content in milk (4.56 %, p ≤ 0.05) compared to cows with FASNAA (+0.29 %). Cows with the TG5CT genotype had a higher protein content (3.32 %, p ≤ 0.001) compared to cows with the TG5CC variant (+0.12 %). All animals studied were dairy cows, with the highest production typicality coefficients found in cows with the FASNAG (4.3, p ≤ 0.01), TG5TT (4.6), and Pit1AA (4.5) genotypes. Cows with a combination of the FASNAG, TG5TT, and Pit1AA genetic variants can be classified as high-yielding dairy cows based on their production typicality coefficients. The data obtained are necessary for assessing the genetic structure of the breed and can be used in planning breeding efforts.