The efficacy of
doxycycline was investigated in two sets of experiments. In the first experiment 40, in the second experiment 60, hence altogether 100 five-week-old Ross broilers of both sexes were used. The birds were randomly allocated into groups (A and B in experiment 1; A, B and C in experiment 2) of 20 birds in each. All birds were infected intramuscularly with approx. 2 x 10(3) colony forming units of Pasteurella multocida strain X-73 (serotype A:1). Birds in groups A were non-medicated controls. Chickens in groups B were given
doxycycline via the
drinking water at a dose of 10 mg/kg
body weight for 5 days, while group C was treated with
chlortetracycline at a dose of 20 mg/kg
body weight for 5 days. The trial lasted for 9 days, then the surviving chickens were sacrificed. Clinical symptoms, number of deaths, post mortem lesions and bacteriological findings were recorded using a special score system. Acute fowl
cholera developed in broilers within a few hours after
infection, as evidenced by the clinical symptoms, the high mortality rate (90% of the birds died within 4 days after
infection), the pathological lesions and the recovery of P. multocida from the challenged birds.
Doxycycline reduced the number of deaths (30% and 5% of birds died in experiments 1 and 2, respectively) and the severity of the clinical symptoms, and P. multocida could be re-isolated only from one of the survivors. In contrast,
chlortetracycline slightly influenced the mortality; however, it delayed death and reduced the severity of clinical symptoms. These data indicate that
doxycycline is highly effective for the treatment of experimental
pasteurellosis in chickens.