World Science and Research PublishingGlobal Journal of Animal Scientific Research2345-43772220140511Study of Toll-Like Receptor 9 gene polymorphism and its association with mastitis disease in the Holstein cows143150ENMohammadMahmoudzadehdepartment of animal science, birjand university. msoorena@gmail.comMohammad bagherMontazer torbatiHomayounFarhangfarArashOmidi201405032014050820140507Mastitis is causes considerable economic losses due to decrease in the quality and quantity of milk production, increases of the cost of treatment and veterinary services, and animal waste (increases of waste product). Inflammation of the udder caused by a traumatic event, toxic agent, or invasion of microorganisms may be indicated by an increase in numbers of somatic cells in milk. Bovine TLR9 is located on BTA22. The TLR9 mRNA consists of two exons and is 3255 bp including 5′ and 3′ UTRs, The genomic size of TLR9 is 4264 bp and the protein is 1029 aa. Blood samples were collected from 150 dairy cattle from six herds. DNA extraction was performed by salting out method. A fragment of 245 bp from intron 1 was amplified by the polymerase chain reaction and analyzed by single-strand conformation polymorphism to get the patterns of single-stranded DNA separated by native polyacrylamide gel electrophoresis and visualized by silver staining. Nine genotypes were revealed with the frequencies of 0.8150 (AA), 0.1481 (AB), 0.2666 (AC), 0.1704 (AD), 0.8880 (BB), 0.1480 (BC), 0.5920 (BD), 0.2960 (CC) and 0.1407 (CD). The allele frequencies for A, B, C and D were 0.3741, 0.2000, 0.2407 and 0.1852; respectively.Chi-square test didn't confirm Hardy-Weinberg (H-W) equilibrium for this locus. Associations between polymorphisms and the trait studied were evaluated using the MIXED procedure of the SAS 9.1 software. Results showed that the somatic cell score not have a significant association with genotypes of TLR9 gene.