Substantial evidence indicates that innate and acquired defense mechanisms are lowest from 3 wk precalving to 3 wk postcalving. This lowered responsiveness includes aspects of systemic and mammary gland immunity that may account, at least in part, for the increased incidence of peripartum disease. The physical and metabolic stresses of pregnancy, calving, and lactation may contribute to this decrease in host resistance and the subsequent increase in disease incidence. However, variation among cows in their host resistance mechanisms suggests that genotype and phenotype may possibly be used to identify cows that are able to mount beneficial immune responses over the periparturient period. Our own studies suggest that cows may be categorized as high or low responders based on the peripartum antibody responses to ovalbumin and Escherichia coli J5. Low responders were hyporesponsive to these test antigens and had a higher incidence of peripartum diseases, particularly mastitis. In many species, a functional link exists between the immune and endocrine systems, and, during periods of stress or physical injury, neuropeptides and neuroendocrine hormones function as immunomodulators. Initial investigations of peripartum cows reveal positive relationships between growth hormone kinetics and profiles of antibody response. Whether hormone fluctuations during the periparturient period are responsible for the alterations observed in immune responsiveness remains uncertain.

Potential associations were investigated between bovine leucocyte antigen (BoLA) alleles and occurrence of disease. Cows (Holstein n = 835; Jersey n = 66) were examined for polymorphisms of the second exon of the BoLA-DRB3 gene, using the polymerase chain reaction (PCR), followed by digestion of the amplified fragments with three restriction endonucleases. Disease occurrences were recorded for each cow throughout one lactation. Milk somatic cell count data were retrieved through the Dairy Herd Improvement records and converted to somatic cell score (SCS). There were no effects of BoLA alleles on SCS in Jersey cows, but BoLA-DRB3.2*16 was significantly associated (P < or = 0.05) with lower SCS in Holsteins. Since the number of Jerseys was relatively small and prevalence of diseases in this population was low, health records of Jerseys were not analyzed further. BoLA associations with occurrence of disease in Holsteins were investigated using a log-linear model. There was a significant (P < or = 0.05) association between BoLA-DRB3.2*23 and occurrence of severe mastitis, from which coliforms were the most commonly isolated bacteria. The BoLA allele *3 was associated with a lower risk of retained placenta (P < or = 0.05) and alleles *16 (P < or = 0.05) and *22 (P < or = 0.05) with a lower risk of cystic ovarian disease. Although more studies are required to confirm the present findings, it can be concluded that BoLA alleles may have potential usefulness as genetic markers of higher or lower risk of disease occurrence in cows.

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The toxicity of Pasteurella haemolytica culture supernatant for bovine and porcine cells was evaluated by 51Cr release. Sterile bacterial culture supematant was toxic for bovine pulmonary lavage cells, peripheral blood lymphocytes and neutrophils, and cultured peripheral blood mononuclear cells, resulting in marked 51Cr release. Only slight release was induced from cultured Madin-Darby bovine kidney cells, porcine pulmonary lavage cells, peripheral blood mononuclear cells, lymphocytes, or neutrophils. No release was detected with primary bovine spleen cell cultures, bovine erythrocytes, or porcine erythrocytes. The demonstrated specificity of this cytotoxin for bovine leukocytic cells may be important in the pathogenesis of bovine pneumonic pasteurellosis.

A quantitative approach was developed to classify Holstein cows and heifers based on phenotypic variation of serum antibody response and to determine associations with peripartum mastitis. Using an index, 136 cows and heifers were classified into high (Group 1), average (Group 2), or low (Group 3) antibody groups following immunization with ovalbumin at wk -8, -3, and 0 relative to parturition. The ranking of groups based on the quantitative index of serum antibody response to ovalbumin were similar for sera and whey antibody such that Group 1 > Group 2 > Group 3. Animals were also vaccinated with Escherichia coli J5 (Rhône Mérieux, Lenexa, KS) at wk -8 and -3 relative to parturition. The ranking of groups for E. coli J5 was similar to that observed for serum and whey antibody to ovalbumin. Serum and whey IgG1 and IgG2 concentrations were measured at wk 0, 3, and 6 but differences between groups were not significant. There was no occurrence of mastitis for Group 1 animals in two of the herds. In contrast, Group 1 animals from the third herd had the highest occurrence of mastitis; however, these cases all occurred in first-parity heifers. According to pooled data across all herds, Group 3 animals had the highest occurrence of mastitis. Heritability estimates of serum antibody response to ovalbumin varied between 0.32 to 0.64 depending on week relative to parturition. Heritability estimates of serum antibody response to E. coli J5 also varied between 0.13 to 0.88 depending upon week relative to parturition. These results indicate that high peripartum antibody may be beneficial in some herds.