The effect of chemotherapeutic agents on the transmission of ovine chronic non-progressive pneumonia

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Abstract
The effect of several chemotherapeutic agents on the transmission of chronic non-progressive pneumonia to 5- month-old lambs by the intranasal inoculation of pneumonic lung homogenate was investigated during the mid-summer months. Ronidazole, oxytetracycline, tylosin and penicillin suppressed in varying degree the development of lesions and the growth of bacteria and mycoplasmas in the lung. The effect of penicillin was studied in more detail in a second experiment. As expected, it did not prevent Mycoplasma ovipneumoniae from colonising the lung; however, only 1 of 10 animals treated with penicillin (10%)developed moderate gross lesions whereas 7 untreated animals (70%) showed moderate-to-severe lesions at necropsy. Histologically, a focal bronchiolitis with mild subacute pneumonia in surrounding alveoli was seen in four (40%) of the penicillin-treated lambs, whereas the seven untreated lambs with pneumonia showed severe changes characteristic of field cases of the disease. In addition to confirming that this disease may be transmitted with homogenates of pneumonic lung, these results suggest that bacteria as well as mycoplasmas have a role in the pathogenesis of chronic non-progressive pneumonia of lambs in New Zealand.