Clinical and pathologic studies of experimentally induced Pasteurella haemolytica pneumonia in calves

Pasteurella haemolytica pneumonia of the right caudal lung lobe was experimentally induced in 2-week-old Holstein calves (n = 11) by endobronchial inoculation of 7.9 x 10(10) colony-forming units of 6-hour log-phase bacteria. Calves were studied for 72 hours after inoculation. The challenge procedure consistently induced a lesion in the right caudal lung lobe, which was consistent radiographically with results of pathologic examination and a similar volume of bronchography contrast medium. Clinically, the calves developed a significant increase in rectal temperature within 24 hours after inoculation. Seventy-two hours after inoculation, the total WBC counts, absolute band neutrophil counts, monocyte counts, and blood fibrinogen concentrations were significantly higher than normal and albumin concentration was significantly decreased. Necropsy revealed a circular to oblong lesion that was congested, edematous, and firm and occupied 20 to 40% of the right caudal lung lobe. Histologic examination revealed a severe acute inflammatory reaction characterized by cellular exudate and proteinaceous fluid in the alveoli, interlobular septa, and pleura.