Variation in bacterial presence in the respiratory tract of calves suffering from respiratory disease in relation to clinical signs and treatment

Abstract

The aim of this study was to analyse variation in the presence of bacteria in the deeper respiratory tract in relation to clinical signs and the effects of treatment for dairy calves suffering from bovine respiratory disease in the Netherlands. For this purpose dairy calves with clear clinical signs were selected and transtracheal aspirated samples were obtained at the day of inclusion in the study and at a later evaluation moment. Coughing, fever, an increased respiratory rate, increased respiratory sounds and nasal discharge were observed clinical signs for diseased animals. The most commonly cultured bacterium was Pasteurella multocida. Mycoplasma spp., M.haemolytica and T.pyogenes were rarely isolated and H.somni was not detected at all. Variation in severity of acute infection did not result in considerable differences in cultured bacterial species. Changes in bacterial isolation in the evaluation samples were observed for the majority (78%) of the calves that showed improvement of clinical signs. Improvement of clinical signs was not necessarily associated with a decline in isolated bacteria. It was observed that antibiotic treatment can result in a decline in number of isolated bacteria, but despite an antibiotic treatment also an increase in bacteria still being present or contribution of new bacterial species to an infection already started by other pathogens were found. Pasteurella multocida isolates showed susceptibility to 3rd generation cephalosporins, ampi-/amoxicillin, fluoroquinolones, gentamicin, trimethoprim/sulfa, tetracycline/doxycycline, kanamycin, penicillin and spiramycin/tylosin. Resistance against kanamycin, penicillin and spiramycin/tylosin was also detected for some Pasteurella multocida isolates. For M.haemolytica only resistance against tetracycline/doxycycline was observed.