Abstract
BACKGROUND: We describe the occurrence of bacteria associated with bovine respiratory disease (BRD) on Austrian beef operations and compare bacterial culture results from double guarded deep nasopharyngeal swab (DNS) and non-endoscopic bronchoalveolar lavage (BAL) samples. Fifty pre-weaned beef calves from 13 conveniently selected commercial beef operations with a history of BRD were sampled between April and August 2024. From each calf a DNS and a BAL sample was obtained and cultured for Pasteurella multocida, Mannheimia haemolytica, Histophilus somni, Bibersteinia trehalosi, Mannheimia spp. and Mycoplasma bovis. Additionally, a M. bovis specific PCR was carried out on all samples. The objectives of this study were to describe and compare the occurrence of bacteria in DNS and BAL samples from Austrian beef calves on beef operations with a history of BRD, and to determine the agreement between M. bovis culture and PCR test results in these samples. RESULTS: In total, 21 bacterial isolates were obtained from 15 of the 50 DNS samples and 22 isolates from 17 of the 48 BAL samples. P. multocida, Ma. haemolytica, H. somni, B. trehalosi and Mannheimia spp. were isolated from 4, 2, 5, 0, and 3 DNS samples, and from 4, 3, 3, 2, and 1 BAL samples, respectively. M. bovis was cultured most frequently, i.e. from 7/50 DNS samples and 9/48 BAL samples. All PCR positive BAL (21/48) samples showed a PCR positive DNS (26/50) as well. Of the PCR positive samples, M. bovis was cultured in 27% of DNS samples and in 43% of BAL samples. A consistent culture result was found in 4/48 calves from both DNS and BAL samples, with M. bovis identified in all cases. The study showed moderate agreement for M. bovis culture (κ = 0.45) and almost perfect agreement for PCR (κ = 0.88) between DNS and BAL, respectively, but poor agreement for other bacteria (κ=-0.91 - -0.03). CONCLUSIONS: Common BRD-associated bacteria occur on beef operations in Austria even in calves with mild BRD signs. Additionally, BAL and DNS are suitable for bacterial isolation from the respiratory tract and can provide an overview of the BRD-associated bacteria involved on the farm. We detected a poor agreement between the results of bacterial isolation from DNS and BAL samples in this study, except for M. bovis.