Molecular genetic evaluation of jersey cattle productivity in the Timiryazev LTD based on the analysis of CSN2 gene polymorphism

This article presents the results of a molecular genetic analysis of the CSN2 gene. This study reports the findings of a molecular genetic investigation into the CSN2 gene polymorphism and its association with milk production traits in Jersey cattle kept in the commercial herd of Timiryazev LLC, located in the Baltasinsky District of the Republic of Tatarstan. The growing consumer interest in A2 milk, which is devoid of β - casomorphin-7, alongside the need to enhance protein content for cheese production, undersores the timeliness of this research. The aim of the study was to evaluate the frequencies of CSN2 gene genotypes and alleles, as well as to identify the association of genetic variants with milk yield, fat content, and protein content. Blood and milk samples from 174 cows were used. Genotyping was performed using PCR with electrophoresis detection. Fat and protein content were determined using an automated analyzer. All animals were maintained under identical feeding and housing conditions. The genotype distribution was as follows: A1A1 – 19.5% (34 cows), A1A2 – 4.6% (8 cows), and A2A2 – 75.9% (132 cows). The A2 allele frequency was 0.782, and the A1 allele frequency was 0.218. Over a 305-day lactation period, cows produced an average of 6, 693,91 kg of milk, containing 6,31% fat and 3,81 % protein. While A1A2 heterosygotes exhibited the highest yield (7,141.75 kg), this superiority was not statistically confirmed (p>0.05). There were also no significant differences in fat content. However, animals with the A2A2 genotype significantly outperform heterozygotes in protein content (3.95% versus 3.61%, p = 0.0120). The total protein yield of the A2A2 group is highest (264.32 kg), which is 6.5 kg higher than that of A1A2. Selection for the A2A2 genotype will not only allow for the production of beta-casomorphin-7-free milk but also increase the herd's protein yield without reducing milk yield or fat content. The high proportion of the desired genotype (75.9%) allows for the transition to A2 milk within 2-3 generations using bulls with the A2A2 genotype. These results have practical implications for farms focused on producing healthy foods.