Microbiological and histopathological findings in cases of fatal bovine respiratory disease of feedlot cattle in Western Canada

Abstract

The aim of this study was to describe the microbiologic agents and pathologic processes in fatal bovine respiratory disease (BRD) of feedlot cattle and to investigate associations between agents and pathologic processes. Ninety feedlot calves diagnosed at necropsy with BRD and 9 control calves without BRD were examined, using immunohistochemical (IHC) staining and histopathologic studies. Mannheimia haemolytica (MH) (peracute, acute, and subacute cases) and Mycoplasma bovis (MB) (subacute, bronchiolar, and chronic cases) were the most common agents identified in fatal BRD cases. Significant associations (P < 0.10) were detected between microbiologic agents and between agents and pathologic processes. When IHC staining was used, 25/26 (96%) of animals that were positive for bovine viral diarrhea virus (BVDV) were also positive for MH; 12/15 (80 %) of animals that were positive for Histophilus somni (HS) were also positive for MB; and all of the animals that were positive for HS were negative for MH and BVDV. This quantitative pathological study demonstrates that several etiologic agents and pathologic processes are involved in fatal BRD of feedlot cattle.

Figure 1

Definition of bovine respiratory disease (BRD) and control study groups used to examine the microbiological and histopathological findings in cases of fatal BRD of feedlot cattle in western Canada. The definition of the study groups are accompanied by a digital image of the open thoracic cavity and cross section of the lung of animals in the different groups. UF — undifferentiated fever Pneumonia was diagnosed when there was evidence for lung consolidation +/− atelectasis Fibrinous peumonia was diagnosed when there was evidence for lung consolidation, edema, atelectasis, and fibrinous exudate, with or without associated fibrinous pleuritis Lesions indicative of chronic pneumonia included pulmonary abscessation, adhesions, and/or shrinkage (presence of fibrous tissue) Lesions indicative of acute pneumonia included pulmonary edema, swelling, or both Bronchiolar pattern was diagnosed based on the presence of prominent and thickened bronchioles with or without exudate or debris in the lumen, which was detected on gross examination of the cross section of the lung

Figure 2

Percentage of pathogen-positive animals in each study group based on an immunohistochemical staining score cut-off of > 0 in a study of the microbiological and histopathological findings in cases of fatal bovine respiratory disease of feedlot cattle in western Canada. MH — Mannheimia haemolytica MB — Mycoplasma bovis BVDV — bovine viral diarrhea virus HS — Histophilus somni BRSV — bovine respiratory syncytial virus IBRV — infectious bovine rhinotracheitis virus PI3V — parainfluenza-3 virus

Figure 3

Percentage of pathologic process-positive animals in each study group based on histopathologic score cut-offs of > 0, > 1, or > 2 in a study of the microbiological and histopathological findings in cases of fatal bovine respiratory disease of feedlot cattle in western Canada. FP — fibrinonecrotizing pneumonia PL — fibrinous pleuritis BP — suppurative bronchopneumonia IP — acute/subacute interstitial pneumonia HM — hemorrhage BS — bronchiectasis BO — bronchiolitis obliterans CP — chronic suppurative pneumonia BN — bronchiolar necrosis PIP — proliferative interstitial pneumonia OTH — other lesions