Identification of Single Nucleotide Polymorphism in Exon 3 of TLR4 Gene and its Association with Somatic Cell Count in Dairy Cattle

Mastitis is a prevalent inflammatory disease, which can impose extra costs on dairy industry worldwide. Genetic and some environmental factors, have fundamental impacts on this this disease and the resistance against that. TLR4 protein is an extracellular receptor that detects pathogens and stimulates the immune system to respond. This study aimed to identify the polymorphism in exon 3 of the TLR4 gene and investigation the association with the somatic cell count in the milk of Holstein cattle of Moghan agro-industry and livestock company. In this study, 200 Holstein cows were used as two groups (number of each = 100) with low (50000 -150000 cell/ml) and high (> 200000 cell/ml) somatic cell count. The sequencing of exon 3 and mapping it to reference sequence led to the identification of one single nucleotide polymorphism (SNP), the substitution of C nucleotide (frequency equal to 0.145) with T nucleotide (frequency equal to 0.855), that replaced isoleucine with threonine. Statistical analysis revealed that milk of cows with CC genotype had significantly fewer somatic cells than the other two genotypes (p < 0.05). Due to the significant association between identified SNP in exon 3 of the TLR4 gene and somatic cell count in milk, it appears that this gene could be a suitable candidate for breeding programs to increase resistance to mastitis.