One of the methods for preventing the spread of subclinical mastitis in herds is the selection of animals with natural resistance to this disease. This approach is based on genetic predisposition, which determines the individual resistance of cows to various forms of mastitis. The aim of the study was to identify and analyze genomic regions and SNPs presumably associated with the somatic cell count, taking into account their differentiation in the Russian population of Ayrshire cows. The study included 5828 milk and DNA samples from 600 Ayrshire cows from six farms in the Leningrad and Moscow regions. On average, the SCC value was 184.1±12.1 thousand units/ml with fluctuations from 107.6±6.4 thousand units/ml to 272.5±49.4 thousand units/ml. A similar picture was observed in relation to the DSCC indicator with an average value of 31.8±0.7%, a minimum of 25.9±0.8% and a maximum of 47.9±4.2%. The heritability coefficients were calculated for the SCC – 0.207, for the DSCC – 0.085. A significant influence of the factors “Farm”, “Father” and “Lactation period” (p˂0.001) on the level of SCC and DSCC in cows’ milk was revealed. In the course of the study, using the Illumina BovineSNP50 BeadChip DNA chip, SNP profiles of animals were obtained and functional candidate genes were identified. GWAS analysis revealed three SNPs in BTA12 (MYO16, rs42775315), BTA17 (NELL1, rs43178042) and BTA29 (the closest region of the SCLT gene, rs43178042) significantly associated with the number of somatic cells in cows' milk (p 0.00001). Animals with homozygous genotypes for rs42775315 GG (90.3%, 163.1±9.8 thousand units/ml), rs109897445 GG (44.17%, 137.5±11.6 thousand units/ml) and rs43178042 CC (85.0%, 162.6±9.5 thousand units/ml) had lower SCC values. The results obtained provide important information on the genetic mechanisms that determine the predisposition to mastitis in Ayrshire cows.
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