Effect of a Staphylococcus aureus bacterin on serum antibody, new infection, and mammary histology in nonlactating dairy cows.

The influence of a Staphylococcus aureus mastitis vaccine on immunologic status and rate of new IMI was evaluated. At drying off, cows were vaccinated, either intramuscularly or subcutaneously in the area of the supramammary lymph node, or were left as unvaccinated controls; vaccinates received booster injections at 6 wk. Serum antibody concentrations, bacteriologic status, and SCC of quarter milk samples were determined. Four weeks after revaccination, cows were challenged by intramammary infusion of S. aureus and then killed 24 to 72 h later. Mean serum antistaphylococcal antibody titer of vaccinated cows during the trial was 4.7-fold that of controls. Challenge resulted in IMI rates of 92, 36, and 60% for control cows, cows vaccinated intramuscularly, and cows vaccinated in the area of the supramammary lymph node. Vaccination by either route had no influence on mammary parenchymal tissue components compared with controls; however, leukocyte infiltration was greater in quarters from cows vaccinated in the area of the supramammary lymph node than in quarters from unvaccinated controls. Plasma cell populations producing IgG1, IgG2, IgA, and IgM were greatest in quarters of cows vaccinated in the area of the supramammary lymph node followed by those in quarters of cows vaccinated intramuscularly and control cows.