Infection Dynamics of Mycoplasma bovis and Other Respiratory Mycoplasmas in Newly Imported Bulls on Italian Fattening Farms.

Italian beef production is mainly based on a feedlot system where calves are housed with mixed aged cattle often in conditions favourable to bovine respiratory disease (BRD). In Veneto, an indoor system is also used for imported bulls around 300-350 kg. Mycoplasmas, in particular Mycoplasma bovis and Mycoplasma dispar, contribute to BRD in young calves, but their role in the disease in older cattle has not been investigated. In this study, ten heads of cattle were selected from each of the 24 groups kept in 13 different farms. Bulls were sampled by nasal swabbing at 0, 15, and 60 days after arrival for Mycoplasma isolation. Identification was carried out by 16S-rDNA PCR followed by denaturing gradient gel electrophoresis. M. bovis, M. dispar, and M. bovirhinis were identified, and prevalence was analysed by mixed-effects logistic regression models. This showed that most bulls arrived free of M. bovis, but within two weeks, approximately 40% became infected, decreasing to 13% by the last sampling. In contrast, the prevalence of M. dispar was not dependent on time or seasonality, while M. bovirhinis only showed a seasonality-dependent trend. The Italian fattening system creates an ideal environment for infection with M. bovis, probably originating from previously stabled animals.