Use of a breeding bull and absence of a calving pen as risk factors for the presence of Mycoplasma bovis in dairy herds.

Mycoplasma bovis is an important cause of pneumonia and mastitis in cattle throughout the world, often reported as emerging. In absence of an effective vaccine for M. bovis, current prevention and control strategies rely on the identification of risk factors for within- and between-herd spread. The objective of this study was to determine the prevalence of M. bovis in Belgian dairy herds and to identify risk factors associated with a positive PCR or antibody ELISA bulk tank milk (BTM) test. A cross-sectional study was performed in 2016 on 100 dairy farms, analyzing BTM using PCR and antibody ELISA. Information on herd-level risk factors focusing on biosecurity and management were collected through a questionnaire and sourced from the national herd identification system (SANITRACE, Animal Health Service Flanders). Multivariable logistic regression was used to identify herd-level risk factors for the presence of M. bovis DNA and antibodies in BTM. The apparent prevalence on BTM was 7 and 17% for PCR and antibody ELISA, respectively. The true prevalence was 7.1% [95% confidence interval (CI) = 2.1-11.5%] and 24.8% (95% CI = 16.4-33.2%). There was no overlap between ELISA- and PCR-positive farms, resulting in a combined true prevalence of 31.8% of the Belgian farms being in recent contact with M. bovis. Risk factor analysis showed that herds with a breeding bull [M. bovis-positive results for 45.5 and 13.6% of herds with and without a bull, respectively, odds ratio = 4.7 (95% CI = 1.1-19.8)] and without a calving pen [M. bovis-positive result in 52.4 and 20.6% of the herds without and with a calving pen, respectively, odds ratio = 3.7 (95% CI = 1.06-12.5)] had higher odds to harbor M. bovis antigen or antibodies in BTM. In conclusion, the present study points to a several fold increase in the prevalence of M. bovis in Belgian dairy herds. The importance of the breeding bull and calving pen in the between- and within-herd spread of M. bovis might have been underestimated in the past. Focusing on these factors might contribute to more effective control programs in the future.