Efficacy of four enrofloxacin treatment regimens against experimental infection in turkey poults with avian pneumovirus and Ornithobacterium rhinotracheale

Drinking-water treatment with enrofloxacin is widely used to cure respiratory infections in turkeys. The current treatment regimen advises a 5-day treatment at 10 mg/kg body weight. Since enrofloxacin exerts a concentration-dependent activity it might be useful to provide the total treatment dose of 50 mg/kg total dose in a single-day treatment regimen. We therefore assessed whether single-day treatment regimens with 50 mg/kg body weight were clinically equivalent to the advised multiple-day treatment regimen with 10 mg/kg body weight for 5 days. For this purpose, five groups of 16 turkeys, 22 days old, were experimentally inoculated with avian metapneumovirus (APV) and Ornithobacterium rhinotracheale and subsequently treated in the drinking water with enrofloxacin, using either a single-day treatment regimen at 50 mg/kg body weight during a 5-h, 10-h or 20-h period or a standard 5-day treatment regimen at 10 mg/kg body weight/day for 20 h. Although initially all dosage regimens cleared O. rhinotracheale from the trachea, 4 days after onset of treatment O. rhinotracheale bacteria were re-excreted in the single-day regimens but without worsening of the clinical symptoms. The 5-day treatment with 10 mg enrofloxacin/kg in turkeys provided the best results for the treatment of an O. rhinotracheale infection in turkeys by shortening the course and reducing the severity of clinical disease and by eliminating O. rhinotracheale from the respiratory tract without re-emergence. None of the used treatment regimens promoted the selection of bacterial clones with reduced susceptibility or resistance.