Mycoplasma bovis in Swedish dairy herds

Mycoplasma (M.) bovis is an important pathogen causing mastitis, pneumonia, arthritis and otitis media in cattle throughout the world. The aim of this thesis was to gain further knowledge of the prevalence and epidemiology of this infection in Swedish dairy herds, and to evaluate testing strategy to detect infected herds.The first study was a national screening investigating prevalence of M. bovis antibodies and bacterial DNA in BTM in all Swedish dairy herds. We found large regional variations with an apparent prevalence of 3-20% in the southern regions. Large herd size was a risk factor for being antibody positive in BTM and positive herds had a higher calf- and youngstock mortality (2-15 months of age).In the second study, we examined the dynamics of M. bovis over time in herds (n=149) in the south of Sweden. Finding seropositive herds increased when adding samples from primiparous (PP) cows. Large herd size and introduction of cattle were risk factors associated with higher levels of M. bovis antibodies in PP cows.In the third study, a questionnaire was used to investigate association between herd-level antibody status and biosecurity- and management routines. In the participating herds (n=115), being affiliated to the biosecurity program “Smittsäkrad besättning” was associated with M. bovis antibody negative status.The fourth study investigated the patterns of antibody prevalence over time in cows and calves in 35 herds. The association of antibody status in individual cows and milk production was quantified, and we found a reduction in milk production in antibody positive cows. The best testing strategy to find infected herds was to analyse antibodies both in BTM samples and in individual cow samples.The results of this thesis indicate that cost-effective strategies for controlling M. bovis infections could be developed, based on biosecurity and antibody monitoring. Implementing such a control strategy would improve cattle health in Sweden.