Efficacy of Norfloxacin Nicotinate Treatment of Broiler Breeders against Haemophilus paragallinarum

SUMMARY. The efficacy of the antimicrobial drug norfloxacin for treating infectious coryza was examined in 26-week-old male broiler breeders. Chickens were inoculated in the infraorbital sinus with the causal organism, Haemophilus paragallinarum. Four experimental groups were set up: control uninfected chickens, infected untreated chickens, and infected chickens treated for 5 days with either 20 mg norfloxacin/kg bodyweight or 40 mg norfloxacin/ kg body weight. The first clinical signs were seen 24 hr postinfection. Of the observed clinical signs, sinus edema was ameliorated by the treatment, and the percentage of birds presenting sinus edema, sneezing, and increased lacrimation was significantly reduced after treatment. Clinical signs disappeared rapidly and were gone by the second day of treatment. The other signs disappeared gradually over 2 weeks after treatment began. There were no significant differences between the two dosage levels. H. paragallinarum was not reisolated from the infected infraorbital sinuses of birds treated with the higher dose of the drug, whereas the reisolation rate was 17% from those treated with the lower dose and 86% from the infected untreated birds.