The primary agent of mastitis is a wide spectrum of bacterial strains; however, viral-related mastitis has also been reported. The MX dynamin-like GTPase 1 (MX1) gene has been demonstrated to confer positive antiviral responses to many viruses, and may be a suitable candidate gene for the study of disease resistance in dairy cattle. The present study was conducted to investigate the genetic diversity of the MX1 gene in Chinese cattle breeds and its effects on mastitis in Holstein cows. First, polymorphisms were identified in the complete coding region of the bovine MX1 gene in 14 Chinese cattle breeds. An association study was then carried out, utilizing polymorphisms detected in Holstein cows to determine the associations of these single nucleotide polymorphisms (SNPs) with mastitis. We identified 13 previously reported SNPs in Chinese domestic cattle and four of them in Holstein cattle. A novel 12 bp indel was also discovered in Holstein cattle. In addition, haplotype frequencies and linkage disequilibrium of four SNPs detected in Holstein cows were investigated. Analysis of these four SNPs in Chinese Holstein cows revealed two SNPs (g.143181370 T&gt;C and g.143182088 C&gt;T)<br /> significantly (P &lt; 0.05) associated with somatic cell score (SCS). The results indicated that SNPs in the MX1 gene might contribute to the variations observed in the SCS of dairy cattle. Therefore, implementation of these two mutations in selection indexes of the dairy industry might be beneficial by favouring the selection individuals with lower SCS.

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