Response of calves to lung challenge exposure with Pasteurella haemolytica after parenteral or pulmonary immunization

In 3 experiments, calves were vaccinated by intrabronchial or subcutaneous injection of formalinized Pasteurella haemolytica. Immunization was evaluated by assessing the clinical and pathologic responses to pulmonary challenge exposure with live homologous bacteria. Serum and bronchoalveolar washings were titrated for antibody by indirect (antiglobulin) bacterial agglutination. Response to challenge exposure was determined by increased rectal temperature and faster respiratory rate. In all experiments, the most obvious clinical change occurred in challenge-exposed calves which had been vaccinated by the subcutaneous injection of killed P haemolytica with added adjuvant. Also, macroscopic pulmonic lesions were recorded most frequently in calves vaccinated by this route. In all instances, immunization resulted in elevated anti-P haemolytica titers both in lung and serum.