Association of BoLA-DRB3 alleles identified by a sequence-based typing method with mastitis pathogens in Japanese Holstein cows.

The association of the polymorphism of bovine leukocyte antigen (BoLA-DRB3) genes identified by the polymerase chain reaction sequence-based typing (PCR-SBT) method with resistance and susceptibility to mastitis caused by pathogenic bacteria was investigated. Blood samples for DNA extraction were collected from 194 Holstein cows (41 healthy cows and 153 mastitis cows including 24 mixed-infection cows infected with 2 or 3 species of pathogens) from 5 districts of Chiba prefecture, Japan. Sixteen BoLA-DRB3 alleles were detected. The 4 main alleles of DRB3*0101, *1501, 1201, and 1101 constituted 56.8% of the total number of alleles detected. Mastitis cows were divided into 2 groups: group 1 with single-infection cows and group 2 with all mastitis cows including 24 mixed-infection cows. The differences in the frequencies of BoLA-DRB3 alleles and the number of cows homozygous or heterozygous for each BoLA-DRB3 allele between healthy cows and the 2 groups of mastitis cows were evaluated. Furthermore, similar comparisons were performed between healthy cows and the 2 groups of mastitis cows for each mastitis pathogen. It was considered that the 4 alleles, namely, DRB30101, 1501, 1201, and 1101 had specific resistance and susceptibility to 4 different mastitis pathogens. Thus, DRB30101 might be associated with susceptibility to coagulase-negative Staphylococci and Escherichia coli, and DRB31501 might be associated with susceptibility to Escherichia coli. However, DRB31101 might be associated with resistance to Streptococci and coagulase-negative Staphylococci, and DRB31201, with resistance to Streptococci, Escherichia coli, and Staphylococcus aureus.