Comparison of conventional and long-acting oxytetracyclines in prevention of induced Actinobacillus (Haemophilus) pleuropneumoniae infection of growing swine.

These experiments tested the hypothesis that long-acting oxytetracycline (oxytetracycline-LA) was more effective than regular oxytetracycline in preventing porcine pleuropneumonia when administered either 24 or 48 h prior to experimental challenge with virulent strains of Actinobacillus pleuropneumoniae. Two experiments (1 and 2) were conducted using growing pigs (average weight 12-15 kg). Antibiotic treatments were administered once intramuscularly at 20 mg/kg body weight; controls received an equivalent volume of saline. Clinical signs were recorded over seven days, and mortality rates and pathological lesions were analyzed using analysis of variance. Serum oxytetracycline levels were compared 48 and 72 h postinjection. All pigs developed clinical disease following experimental infection. Actinobacillus pleuropneumoniae was recovered from 42% of experiment 1 pigs and all of experiment 2 pigs. The data showed that both oxytetracycline and oxytetracycline-LA given at the same dose protected pigs against experimental infection when given 24 h prior to challenge, and there was no difference between the efficacy of the two drugs in this experiment. When administered 48 h prior to challenge, only oxytetracycline-LA reduced the clinical signs and pathological changes following A. pleuropneumoniae challenge. Between 48 and 72 h postinjection, oxytetracycline-LA blood levels were significantly greater compared to oxytetracycline-treated pigs.