Mycoplasma bovis and Mannheimia haemolytica dynamics during acute bovine respiratory disease in feedlot cattle

Mycoplasma bovis is a bacterium member of the family Myco­plasmataceae, characterized by a small genome, lack of cell wall, and high nutritional requirements for in vitro growth (Li et al., 2011; Parker et al., 2018; Dudek et al., 2020). Traditionally, M. bovis has been linked to chronic BRD cases and treatment failures (Booker et al., 2008; Hermeyer et al., 2012; Gershwin et al., 2015; Becker et al., 2020). Several virulence factors have been implicated in M. bovis ability to persist in the lungs of cat­tle with BRD, such as variable surface proteins (Vsp), adhesins, nucleases, H2O2 production and biofilm formation (Burki et al., 2015; Perez-Casal, 2020). Due to the difficulties of growing M. bovis in the lab, the inherent culture bias (Prakash et al., 2021) could have shaped our current knowledge of M. bovis in BRD. Recent evidence has emerged linking M. bovis presence in the upper respiratory tract with acute BRD status (Timsit et al., 2018; Centeno-Martinez et al., 2022). However, the association between M. bovis and other BRD agents, especially Mannheim­ia haemolytica, over time remains unknown during the first month on the feedlot. A more comprehensive understanding of the dependencies among BRD pathogens over time will help develop new non-antibiotic control strategies and subsequently reduce the burden of BRD on beef cattle production. Therefore, this study aimed to evaluate the association of M. bovis and M. haemolytica during acute BRD in feedlot cattle.