Efficacy of florfenicol on experimental Actinobacillus pleuropneumonia in pigs

The efficacy of florfenicol was evaluated on experimental Actinobacillus pleuropneumonia in 5 to 7-week-old pigs. All pigs were intranasally inoculated with bacterial suspension containing 10(8) or 10(9) colony forming units of Actinobacillus pleuropneumoniae, Fukushima (serotype 2), Shope4074 (serotype 1), K17 (serotype 5), 8541 or 8543 (serotype 2; thiamphenicol-resistant strain). Florfenicol and thiamphenicol were given in feed for 12 days, from 5 days before inoculation to 7 days post inoculation (at necropsy). More than half the pigs died in the infected control groups, while no pigs died in florfenicol 50 ppm groups inoculated with each strain. On inoculation with thiamphenicol-sensitive strains, Fukushima, Shope4074 and K17, the average total score of clinical signs and percentage of lung lesion area in florfenicol 50 ppm groups were significantly lower than those in the infected control groups (P < 0.05). On inoculation with thiamphenicol-resistant strains, 8541 and 8543, the average total score of clinical signs and percentage of lung lesion area in florfenicol 50 ppm groups were significantly lower than those in the infected control and thiamphenicol 200 ppm groups (P < 0.05). The development of pleuropneumonia was remarkably prevented by medication with feed containing florfenicol in pigs inoculated with serotype 1, 2, 5 strains and thiamphenicol-resistant strains of A. pleuropneumoniae.