Relationships between genetic measures of mastitis (somatic cell score, score for clinical mastitis, and scores for IMI with major or minor pathogens) and immunological parameters (physiological and molecular markers) were examined for periparturient Holstein cows. Physiological markers included 11 in vitro immunological assays. Molecular markers included the second exon of the DRB3 locus of the bovine major histocompatibility complex, the IgG2 isotype genotype, and the CD18 genotype (the locus responsible for bovine leukocyte adhesion deficiency). A gene substitution model was used to estimate the additive genetic effects of alleles of the three molecular markers on estimated breeding value (EBV) for mastitis measures. Pearson correlation coefficients between EBV for immunological assays and EBV for mastitis measures were computed. Molecular markers explained up to 40% of the variation in EBV for measures of mastitis. The presence of allele DRB3.2*16 was associated with higher EBV for SCS. Allele DRB3.2*8 was associated with increased EBV for clinical mastitis, as was the IgG2b allele and the normal CD18 allele. Alleles DRB3.2*11, *23, IgG2a, and the recessive allele for bovine leukocyte adhesion deficiency were associated with decreased clinical mastitis. A positive genetic association was found between allele DRB3.2*24 and EBV for IMI by major pathogens and between DRB3.2*3 and IMI by minor pathogens. Several correlations between EBV for immunological assays and EBV for mastitis measures were significantly different from 0. Cows with low EBV for SCS tended to have neutrophils that had greater functional ability at maximal immunosuppression, low serum IgG1, and high numbers of circulating mononuclear cells. Immunological parameters, including physiological and molecular markers, are useful aids to understand the genetics of resistance to mastitis.

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The associations between alleles at the BoLA (bovine lymphocyte antigen) DRB3 locus and 20 indicator traits of innate and adaptive immunity were investigated. Periparturient Holsteins (n = 127) were genotyped at the BoLA DRB3 locus using polymerase chain reaction and restriction fragment length polymorphism. Twenty-two alleles were observed in the study population, and frequencies ranged from 21 to < 1%. The same cattle were tested for a total of 20 innate and adaptive immunity traits, including lymphocyte response to mitogens (proliferative responses and Ig secretion), serum Ig, complement and conglutinin concentrations, total leukocyte count, and selected assays for neutrophil function. Models with gene substitution effects were used to investigate associations between BoLA DRB3 alleles and each of the immunological variables. Significant associations were found with 13 of the leukocyte functions tested. The number of immune parameters with significant associations with any allele ranged from 0 (with alleles DRB3.2*23 and DRB3.2*27) to 7 (with DRB3.2*8). The immunological parameter that had the most associations with alleles was serum IgG2 concentration with 6 alleles. One group of 4 alleles (representing 46% of the total allele frequency) was uniformly associated with increased IgM and complement and decreased mononuclear cell numbers. Thus, we demonstrated that the BoLA DRB3 genotype can influence measures of innate and adaptive immunity.

The genetic variability of blood neutrophil functions, lymphocyte blastogenic responses to mitogens, serum Ig concentrations, and serum complement and conglutinin activities was investigated from 35 d prepartum to 35 d postpartum for 137 Holstein cows. Periparturient cows experience an immunosuppression of various immunologic parameters at calving. Heritability estimates were obtained before, during, and after the episodes of immunosuppression. Significant genetic variability occurred in the periparturient changes for total number of neutrophils, neutrophil chemokinesis, assays of the neutrophil respiratory burst associated with phagocytosis (cytochrome c reduction, chemiluminescence, and iodination), serum concentrations of IgG1, IgG2, and IgM, and serum homolytic complement activity. This variability implies that immune profiles could be used for the selection of cattle with improved innate immune response without adverse effects on milk productivity. These results should be considered tentative, however, because the number of observations included in the data were limited.

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