COMPARISON OF RADIOGRAPHIC AND NECROPSY FINDINGS OF LUNG LESIONS IN CALVES AFTER CHALLENGE EXPOSURE WITH PASTEURELLA-MULTOCIDA

Objectives-To test suitability of radiographic evaluation of lung lesi ons as a substitute for lung lesion scores derived by examination at n ecropsy in challenge-exposure models of bovine pneumonia. Animals-10 c arves selected by body weight from 20 multiple-source male Holstein ca lves approximately 1 to 2 months old enrolled in a Pasteurella multoci da challenge-exposure study. Procedure-Calves were paired on the basis of weight and randomly assigned within pairs to vaccine or control (s aline solution) group. By use of deep tracheal cannulation, carves wer e challenge exposed with a culture of virulent P multocida, observed f or 10 days, euthanatized, and necropsied, and the lungs were scored fo r pneumonic lesions. Radiographic views of the lung fields of the calv es were taken before challenge exposure and before necropsy and were e valuated for alveolar disease by a veterinary radiologist. Lung lesion scores were compared with radiographic evaluations. Results-There was a strong and significant correlation (R-2 = 0.91, P < 0.001) between results of the evaluation of postchallenge-exposure radiographs and ne cropsy results. There also was also strong and significant correlation (R-2 = 0.90, P < 0.001) between evaluation of the prechallenge-exposu re radiographs and necropsy results. Conclusions-Radiographic evaluati on of lung lesions correlates well with lung lesions found at necropsy . The findings emphasize the need for caution in interpreting the resu lts of challenge-exposure studies of bovine respiratory tract disease in which small numbers of calves are studied.