The Microbial flora of the upper and lower respiratory tracts of feedlot calves with undifferentiated bovine respiratory disease

Abstract

The upper and lower respiratory tracts of feedlot calves with (59 cases) and without (60 controls) signs of undifferentiated bovine respiratory disease were sampled before and after antibiotic treatment (penicillin, trimethoprim-sulfadoxine) using nasopharyngeal swabs (NS) and bronchoalveolar lavage (BAL). Samples were cultured for bacteria and mycoplasmas. Pathogens were present in the lungs of sick and control calves. Pasteurella multocida was associated with morbidity. At a group level NS cultures were reliable predictors of BAL culture. P. haemolytica isolated after treatment were frequently resistant to a combination of penicillin, ampicillin and tetracyclines. Bacteria but not mycoplasms were largely cleared from the lungs after therapy but later some recolonization occurred. Treatment failure was seldom associated with antimicrobial resistance.