Molecular surveillance of Mycoplasmopsis bovis across dairy farms in Western Canada and 16S microbiome assessment in pneumonic calves

Mycoplasmopsis bovis is an important bacterial pathogen that severely affects the Canadian dairy industry and has been linked to bovine respiratory disease (BRD), a complex that includes pneumonia, as well as mastitis, otitis media, and arthritis. Despite its clinical relevance, limited data exists on its prevalence in Western Canadian dairy herds, and its role within the microbiome in the context of pneumonia remains unclear. This study aimed to determine the prevalence of M. bovis in British Columbia and Alberta and to assess microbial shifts in pneumonic calves to investigate its potential role in BRD. A total of 60 farms were screened for M. bovis using quantitative real-time PCR on bulk tank milk (BTM) and swab samples. Mycoplasmopsis bovis DNA was detected in 20% of screened farms. However, there were notable differences in detection between swab and BTM samples, highlighting the importance of considering both sample types in surveillance initiatives. Additionally, 82 swab samples from calves in a single herd were analyzed using 16S rRNA sequencing to compare microbial communities across clinical groups. Microbial diversity, differential abundance (Analysis of Compositions of Microbiomes with Bias Correction 2), and taxa correlations (Sparse Estimation of Correlations among Microbiomes) were assessed. Mycoplasmopsis bovis presence was not significantly associated with clinical status, although calves with pneumonia exhibited significantly altered microbial diversity compared with healthy calves. Mycoplasmopsis bovis abundance was significantly enriched, and several commensal taxa were significantly depleted in the pneumonic microbiome. Mycoplasmopsis bovis abundance was also inversely correlated with some of these taxa, supporting a role in dysbiosis. Overall, these findings suggest that M. bovis is associated with dysbiosis within the respiratory microbiota and may contribute to BRD pathogenesis under conditions of microbial disruption.