Abstract: The assay was aimed to explore the effects of different doses of florfenicol on immunity effects of Newcastle disease live vaccine, determine the florfenicol optimal dosage, and provide scientific basis for the clinical application of florfenicol. 150 broilers of 14-day-old were divided into 5 groups (control group, groupsⅠ, Ⅱ, Ⅲ and Ⅳ). The control group normally drank water, groupsⅠ, Ⅱ, Ⅲ, Ⅳ respectively added water-soluble florfenicol 50，100，200，400 mg/L in the drinking water, through the determination of serum antibody titer of Newcastle disease, IL-10 and INF-γ contents, we analyzed the immune effect of different doses of florfenicol on Newcastle disease live vaccine. The test results showed, compared with control group, serum antibody titers of Newcastle disease, IL-10 and INF-γ contents of groups Ⅰ and Ⅱ had no significant differences (P＞0.05), but groups Ⅲ and Ⅳ had significant differences (P＜0.05). Low doses of florfenicol added in drinking water (50,100 mg/L) had no effect on immune effect of Newcastle disease live vaccine, but high doses of florfenicol (200,400 mg/L) had immunosuppression on immune effect of Newcastle disease live vaccine.

Key words: florfenicol; Newcastle disease; immunosuppression