A subclinical pneumonia of calves associated with Mycoplasma dispar.
The macroscopic lung lesions consisted of scattered lobular areas of atelectasis which were more numerous and extensive in the right apical lobe. Microscopic changes observed were septal cell hyperplasia and proliferation, bronchiolitis and perivascular and peribronchial lymphoreticular hyperplasia. Gross and microscopic lesions were more pronounced in calves 7-16 weeks of age than in calves aged 1-6 weeks or 20 weeks. Intratracheal inoculation of caesarean-derived or colostrum-deprived calves with a homogenate of affected lung or with cultures of M. dispar resulted in a proliferative interstitial pneumonia.