| This study determined the prevalence of diseases and pathogens causing mortality in Ontario beef feedlot calves, the lesions associated with Mycoplasma bovis pneumonia and arthritis, and the correlation between bovine viral diarrhea virus (BVDV) infection and M. bovis pneumonia (MbP). Ninety-nine calves that died or were euthanized within 60 days after introduction into 72-feedlots were investigated, between October 2001 and January 2002. Calves died due to pneumonic pasteurellosis (PP) (32%), Mycoplasma bovis pneumonia and arthritis (24%), combination of MbP and PP (11%), viral pneumonia (VP) (5%), disease caused by BVDV infection (7%), Histophilus somni myocarditis (6%), ruminal bloat (2%), and miscellaneous diseases (8%). Lesions of pneumonia identified in 86/99 calves included MbP (24%), concurrent MbP and PP (30%), PP without MbP (28%), and uncomplicated VP (4%). Viral infections identified were: BVDV (35%), bovine respiratory syncytial virus (9%), bovine herpesvirus-1 (6%), parainfluenza-3 virus (3%), and bovine coronavirus (2%). From the lungs of 99 calves, there were isolated M. bovis (82%), Mycoplasma arginini (72%), Ureaplasma diversum (15%), Mannheimia haemolytica (26%), Pasteurella multocida (19%), H. somni (14%), and Arcanobacterium pyogenes (19%). Immunohistochemistry of skin detected persistent BVDV infection in 12% of cases. BVDV infection was detected in 57% of calves with PP, 40% of calves with concurrent MbP and PP, 21% of calves with MbP, and in 15% of calves without pneumonic lesions. These findings indicate that bronchopneumonia is the most frequent cause of mortality of beef calves during the first two months after arrival in feedlots, accounting for 70% of total deaths. The prevalence of MbP approached that of PP, and both diseases were the most common causes of pneumonia and mortality. Mycoplasma bovis pneumonia and polyarthritis has emerged as an important cause of death losses for Ontario beef feedlots. Lung lesions of Gaseous necrosis, bronchiectasis, pyogranulomatous bronchiolitis and peribronchiolar lymphocytic cuffing were the most common findings in lungs with MbP. BVDV infection was more frequently identified in calves that died of bronchopneumonia than in calves dying with any other disease (except BVD disease), but there was no greater prevalence of BVDV infection in calves with MbP than in calves with PP. |
