This study investigated the efficacy of Allium fistulosum L. powder supplemented in the basal diet on the immune response against the Newcastle Disease (ND) virus and the growth performance of the local chickens. Oneday-
old chicks (n=400) were allocated to a completely randomized design with four replicates of five treatments. Chickens in treatment T1 were not supplemented with any powder in the basal diet. Chickens in treatment T2 were supplemented with chlortetracycline with 10 mg/kg feed. Chickens in treatment T3, T4, and T5 were supplemented with A. fistulosum L. powder with 5 g/kg, 10 g/kg, and 15 g/kg feed, respectively. The experiment lasted 14 weeks. All chickens were vaccinated against Newcastle Disease on days 7, 21, and 60. Sixteen blood samples were taken from each treatment on days 49, 74, and 81. The HI test measured the serum antibody level against the Newcastle disease virus. The results showed that A. fistulosum L. powder supplementation (10 g/kg) in the basal diet increased the antibody titer against, while chlortetracycline (10 mg/kg) in the basal diet had a low antibody titer against ND virus in chickens on 49 days of age. Feed intake and feed conversion ratio were similar among the five treatments. Weight gain was significantly different among the five treatments. Weight gain was significantly higher in T2, T3, and T5 treatments than in control treatment T1. The supplementation of A. fistulosum L. powder at 5 g/kg and 15 g/kg feed improved the weight gain of chickens.