Identification of genetic polymorphism of the MBL2 gene and its association with clinical mastitis in Murrah buffaloes

Mastitis is a serious bovine disease which causes significant commercial loss. Polymorphism of mannose-binding lectin genes in bovine may be regarded as a functional and positional candidate gene for mastitis resistance and complement activity. In the present study, single-nucleotide polymorphism (SNP) of MBL2 gene in 200 Murrah buffaloes was investigated using the polymerase chain reaction direct sequence (PCR direct sequence) technique, and four new SNPs at 1262G>A, 3382A>T, 4387C>T and 4511C>T loci of Mannose binding lectin 2 (MBL2) gene were found. Pair linkage disequilibrium analysis and haplotype construction of MBL2 gene were performed using SHEsis software. Two nonsynonymous types of changes were observed at 1262G>A (Gly40Asp) and 4387C>T (Thr166Met) of MBL2 protein. These amino acid changes were however predicted not to affect the protein function in any manner. An odds ratio analysis showed that the A allele of 1262G>A, A allele of 3382A>T, C allele of 4387C>T and C allele of 4511C>T had 3.7, 5.19, 7.82 and 3.7 fold increased risk for developing clinical mastitis in Murrah buffaloes, respectively, identifying that these alleles are 'at-risk' alleles and showed significant association with increased risk for clinical mastitis in Murrah buffaloes (P< 0.01). Genotypic association analysis revealed that Murrah buffaloes with AG, AT, CT and TT genotypes at 1262G>A, 3382A>T, 4387C>T and 4511C>T loci of MBL2 gene, respectively were found significantly least susceptible to clinical mastitis compared to other genotypes. A total of seven haplotypes were constructed from four SNPs of MBL2 gene. Haplotypes association analysis showed that animals with allelic combination of haplotypes Hap6 (GTCT) and Hap7 (GTTT) were significantly least susceptible to clinical mastitis compared to other haplotypes in Murrah buffaloes (P< 0.01).