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.