Epidemiology and clinical significance of Mycoplasma bovis infection in calf feedlots in Spain.

Abstract

The presence, dynamics and persistence of Mycoplasma (M.) bovis in 12 batches of grazing calves during the first month of stay at the feedlots was analyzed. Nasopharyngeal swabs were weekly collected between days 0 and 28 to detect the presence of M. bovis by culture and PCR. The animals were daily monitored for the presence of respiratory disease. The results showed the presence of different epidemiological situations at arrival, detecting the presence of uninfected or with a low prevalence groups or batches with a variable prevalence (13.3-86.7 %). Subsequently, at least one calf scored positive in all the batches 14 days after arrival and almost all calves (n = 166) resulted infected after 28 days. Calves infected with M. bovis tested positive in 3 of the 5 samples taken (mean 3.06). The presence of respiratory signs was statistically significant in infected vs. uninfected ones, with symptoms appearing earlier in batches where the initial prevalence of M. bovis was higher. The molecular characterization of the isolates confirmed the presence of more than one biotype circulating in the same batch or even calf, which could be associated to the presence of more severe clinical findings. Most of the isolates were classified as biotype st-3 but three biotypes were detected, resulting all of them multiresistant to macrolides, tetracyclines and lincomycin with a variable sensitivity to quinolones. Overall, the frequency of M. bovis infection highlights its significant epidemiological role in bovine respiratory diseases in calf fattening.