Methods: Two hundred and forty, 1-day-old, hatched Ross broilers received a maize-soybean meal basal diet and were allocated randomly in the following five experimental treatments for 6 weeks: basal diet-no additives, basal diet containing 1 g anise/kg diet, basal diet containing 5 g anise/kg diet, basal diet containing 10 g anise/kg diet and basal diet containing flavophospholipol at 4.5 mg/kg diet. At Day 42, two birds per replicate were slaughtered for determination of carcass and organ weights. At Day 28, serum antibody titers against avian influenza virus were measured by the hemagglutination inhibition test.