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

Beta-2-microglobulin (beta 2m) 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 beta 2m and the association of SNPs genotypes as well as haplotypes with milk IgG1 concentration and mass. Blood DNA from 189 Chinese Holstein daily cows was extracted, sequenced and genotyping was analyzed. Milk IgG1 concentrations from these cows were determined by ELISA and evaluated with respect to their beta 2m 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 beta 2m were found to be correlated (P<0.05) with milk IgG1 concentration and mass. Dairy cows with homozygous deletion of beta 2m had the lowest milk IgG1 concentration and mass. These results indicate that beta 2m genotypes could serve as a marker to identify dairy cows with high IgG1 milk levels. (C) 2011 Elsevier B.V. All rights reserved.