The clinical efficacy of enrofloxacin in the treatment of experimental bovine pneumonic pasteurellosis.

The clinical efficacy of enrofloxacin was tested in calves with experimentally induced pneumonic pasteurellosis. A strain of Pasteurella haemolytica, biotype A, serotype 1 (P. haemolytica A1), which had been isolated from an outbreak of pneumonic pasteurellosis in feedlot calves, was used to induce the disease in 24 eight-month-old calves. Each animal received, by intratracheal injection, 6 x 10(11) colony forming units of P. haemolytica A1 in a four-hour log phase culture. Twelve similar animals were kept as non-infected controls (Negative Control group). Treatment of the infected animals commenced 40 h after infection and was as follows: 12 animals each received 2.5 mg/kg enrofloxacin subcutaneously and 12 animals each received 5 ml sterile saline intramuscularly (Positive Control group). All treatments were given once daily for three consecutive days. Clinical examinations were performed on all animals once daily, starting prior to infection and continuing until 12 d post-infection. The parameters evaluated were rectal temperature, habitus (attitude), ocular mucous membrane congestion and abnormal sounds on lung auscultation. On day 14 post-infection, all animals were killed and their lung lesions (if any) estimated as the percentage involvement of each pair of lungs. The only statistically significant (P > or = 0.05) differences observed were between the Negative Control group and the Positive Control group. Noticeable differences were seen between the enrofloxacin-treated group and the Positive Control group, but they were not statistically significant (P > 0.05). The average lung lesion score (pneumonic lesions as a percentage of total lung volume) for the Positive Control group was 12.1% and that of the enrofloxacin-treated group, 8.4%. This difference was not statistically significant (P > 0.05).