Efficacy of spectinomycin against Mycoplasma bovis induced pneumonia in conventionally reared calves

Sixteen 3-week-old calves were intratracheally inoculated with Mycoplasma b ovis. Follow-up consisted of regular bronchoalveolar lavages (BALs) and cli nical examinations. Animals were slaughtered from 4 to 21 days after inocul ation. Counts were made of the mycoplasmas and other bacteria systematicall y isolated from the BAL liquids and lung lobes after slaughter. On the 6th day, spectinomycin 20 mg/kg was given intramuscularly in three repeated dos es at 24 h intervals to six randomly chosen calves. All animals had develop ed a persistent M, bovis infection with a maximum BAL count on the 6th day (start of treatment). Co-occuring Pasteurella multocida infection was found in most animals with a maximum rate on the 13th day. The extent of lung su rface lesions varied widely (0-64%) but was greater in the later slaughtere d calves. Average counts of M. bovis and P. multocida in the BAL liquids we re lower in treated calves than in untreated ones but the difference was no t statistically significant. However, M. bovis and P. multocida counts in t he lungs of the treated group were significantly lower than in the untreate d group (p = 0.003 and 0.009. respectively), (C) 2001 Elsevier Science B.V. All rights reserved.