Sequential titration of bovine lung and serum antibodies after parenteral or pulmonary inoculation with Pasteurella haemolytica.

Calves were vaccinated by intrabronchial or subcutaneous injection of formalinized Pasteurella haemolytica. Antibody in serum, nasal washings, and bronchoalveolar washings was titrated sequentially before and after calves were vaccinated and then challenge exposed with live homologous bacteria. Bronchoalveolar washings were collected by fiberoptics bronchoscopy, and antibody was titrated by indirect (antiglobulin) bacterial agglutination. Responsiveness to vaccination was related in initial serum antibody concentrations. Calves with serum antibody titers of 1:20 or more were nonresponsive, whereas with few exceptions, calves having titers of less than 1:20 responded to vaccination. Results indicated that serum and lung antibody were induced by subcutaneous or by intrabronchial inoculation of formalinized P haemolytica. By either route of immunization, serum antibody was more persistent than was lung antibody, and pulmonary challenge exposure with live P haemolytica did not alter existing titers.