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Prevalence and genotype of Mycoplasma bovis in beef cattle after arrival at a feedlot

Castillo-Alcala, Fernanda, Bateman, Kenneth G., Cai, Hugh Y., Schott, Courtney R., Parker, Lois, Clark, Mary Ellen, McRaild, Patricia, McDowall, Rebecca M., Foster, Robert A., Archambault, Marie, Caswell, Jeff L.
American journal of veterinary research 2012 v.73 no.12 pp. 1932-1943
Mycoplasma bovis, amplified fragment length polymorphism, beef cattle, calves, feedlots, genotype, lungs, pneumonia, quantitative polymerase chain reaction
Objective: To determine the prevalence of Mycoplasma bovis infection in the lungs of cattle at various times after arrival at a feedlot, to measure the relationship between clinical disease status and the concentration and genotype of M bovis within the lungs, and to investigate changes in the genotype of M bovis over time. Sample: Bronchoalveolar lavage fluid (BALF) from 328 healthy or pneumonic beef cattle and 20 M bovis isolates obtained from postmortem samples. Procedures: The concentration of M bovis in BALF was determined via real-time PCR assays, and M bovis isolates from BALF were genotyped via amplified fragment length polymorphism (AFLP) analysis. Results: Prevalence of M bovis in BALF was 1 of 60 (1.7%) at arrival to a feedlot and 26 of 36 (72.2%) and 36 of 42 (85.7%) at ≤ 15 days and 55 days after arrival, respectively. Neither the concentration nor the AFLP type of M bovis in BALF was correlated with clinical disease status. The M bovis AFLP type differed between early and later sampling periods in 14 of 17 cattle. Conclusions and Clinical Relevance: The findings implied spread of M bovis among calves and suggested that host factors and copathogens may determine disease outcomes in infected calves. Chronic pulmonary infection with M bovis may represent a dynamic situation of bacterial clearance and reinfection with strains of different AFLP type, rather than continuous infection with a single clone. These findings impact our understanding of why cattle with chronic pneumonia and polyarthritis syndrome inadequately respond to antimicrobial treatment.