Abstract Introduction: The purpose of the present study is to identify and investigate the A2 allele of the betacasein gene in Holstein dairy cows and its relationship with milk somatic cells. Materials and Methods: In this study, 89 Holstein cows were used. DNA extraction was done from milk blood samples. The quantity and quality of the extracted DNAs were checked using spectrometry and electrophoresis. PCR-RFLP method was used to check the genotype of beta-casein, as well as sequencing was used for the accuracy of the genotyping results. Finally, one-way analysis of variance was performed to investigate the relationship between the A2 allele and the number of body cells using JMP software version 0.17. Tukey\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'s test with a significance level of 5% was used to compare the means. Results and discussion: The results showed that out of the 89 cows, 14 cows (15.7%) lacked betacasein A2 gene, 22 cows (24.7%) were homozygous and 53 cows (59.5%) were heterozygous. The frequency of A2 allele was calculated as 0.388. Statistical analysis also did not show a significant relationship between the A2 allele and the number of body cells (P<0.05). Conclusion: Considering the possibility of favorable effects of A2 allele on human health, and the absence of a negative relationship between this allele and important traits of milk, it is necessary to use study programs to increase the genetic and genotypic frequency of this allele so that the mentioned genetic potential can be used to maintain health. Society is interested in improved cows.

کلمات کلیدی