Association of polymorphisms of beta-2-microglobulin gene (β2m) with milk IgG1 content in Chinese Holstein dairy cows

Beta-2-microglobulin (β2m) is an integral component of the Fc receptor (FcRn) heterodimer which is involved in IgG transfer across mammary epithelial cells. The aim of this study was to estimate the frequency of alleles of β2m and the association of SNPs genotypes as well as haplotypes with milk IgG1 concentration and mass. Blood DNA from 189 Chinese Holstein dairy cows was extracted, sequenced and genotyping was analyzed. Milk IgG1 concentrations from these cows were determined by ELISA and evaluated with respect to their β2m genotypes. The results showed that two single nucleotide polymorphisms (SNPs) and one insertion/deletion (indel) of two base pairs, assorted into four haplotypes, were identified. The genotypes and haplotypes of β2m were found to be correlated (P < 0.05) with milk IgG1 concentration and mass. Dairy cows with homozygous deletion of β2m had the lowest milk IgG1 concentration and mass. These results indicate that β2m genotypes could serve as a marker to identify dairy cows with high IgG1 milk levels.