Pulmonary lesions induced by Pasteurella hemolytica in cattle.

Twelve four month old calves were inoculated intratracheally with a large dose of Pasteurella hemolytica and the lungs examined 18 hours, three days and seven days later. The gross and microscopic lesions were graded in each calf. The most extensive gross lesions were present at three days and were characteristic of a fibrinous pneumonia. Discrete areas of coagulation necrosis were present at three days and granulation tissue had formed around these by seven days. Characteristic swirly dark cells accumulated in alveoli and alveolar ducts and were observed from three days onwards. The gross and microscopic lesions were similar to those seen in field cases of pneumonic pasteurellosis.