Mycoplasma bovis is associated with Mannheimia haemolytica during acute bovine respiratory disease in feedlot cattle

Abstract

Bovine Respiratory Disease (BRD) represents a significant burden to the health of feedlot cattle and the profitability of the beef industry in the US.Mannheimia haemolyticais widely regarded as the primary bacterial pathogen driving acute BRD. WhileMycoplasma bovisis most commonly implicated in chronic cases of BRD, this agent's potential role in acute stages of BRD is unclear. Therefore, this study aimed to evaluate potential associations betweenM. bovisandM. haemolyticaduring acute BRD in feedlot cattle. Nasal swabs (n= 1,044) were collected over time from feedlot cattle (n= 270) enrolled in an experiment assessing the effect of vaccination for Bovine Respiratory Syncytial Virus (BRSV). Swabs were analyzed for detection ofM. bovis, M. haemolytica, Pasteurella multocida, Histophilus somni, and BRSVviamultiplex qPCR assays. Data were analyzed using inverse conditional probability weighted (ICPW) logistic regression models to investigate potential effects ofM. bovispresence on arrival (d0), day seven (d7) and day 14 (d14) post-arrival onM. haemolyticaprevalence on day 28 (d28) post-arrival, adjusting for the previous history ofP. multocida, H. somni, BRSV, BRD morbidity, and body weight. The potential association between time-to-BRD detection andM. bovispresence on d0, d7, and d14 post-arrival, was inferredviaan ICPW time-to-event model. The presence ofM. bovisin nasal swabs collected on d7 post-arrival was significantly associated with an increase in the prevalence ofM. haemolyticaon d28 (prevalence difference: 45%; 95% Confidence Interval: 31%, 60%;P-value < 0.001). Significant time-varying coefficients forM. bovispresence were detected at d0, d7, and d14 post-arrival in the ICPW time-to-event model (P-value < 0.001). The shortest median time-to-BRD detection was 29 days in cattle that wereM. bovispositive on d0, d7, and d14 post-arrival and in those that were positive on d0 and d14 post-arrival. Under the conditions of this study, our findings suggest thatM. bovismay be influencing the respiratory environment during the acute phase of BRD, increasing the abundance ofM. haemolytica, which could have important impacts on the occurrence of BRD.