The effect of aerosolized bacterial lysate on experimentally induced pneumonia in calves.

Bovine respiratory disease (BRD) often occurs during specific periods of increased susceptibility when stress, viral infection, or reduced air quality are thought to suppress respiratory defences. The innate immune system is rapidly responsive and broadly protective and could be a target for preventing BRD during these periods of increased susceptibility. This study tested the hypothesis that stimulation of pulmonary innate immune responses by aerosol delivery of a lysate of killed and bacteria would protect calves against pneumonia. Ten clean-catch colostrum-deprived Holstein calves were randomly assigned to receive either aerosolized bacterial lysate or saline 24 hours before challenge. Effects of this treatment on clinical, hematologic, microbiologic, and pathologic outcomes were assessed. Compared to controls, lysate-treated calves had lower serum haptoglobin and blood leukocyte and neutrophil concentrations following challenge. There were no differences in temperature, heart and respiratory rates, clinical scores, ultrasound lesions, or number of in the nasal cavity or lung. Thus, treatment with bacterial lysate prior to challenge appeared to ameliorate early measures of inflammation but did not provide sufficient protection to substantially alter the course of disease.