RESUMO
Biosecurity in the production of broiler chickens is very important but it is hard or even impossible to maintain; hence, promotion of immune responses could control diseases in chickens. At present study, the effect of six levels of oil-extracted propolis [0, 50, 100, 150, 200 and 250 mg/kg ration] on immune system against Newcastle virus was studied using a completely randomized design with 360 chickens. Blood antibody ratio against the Newcastle virus [HI test], the weight of thymus, bursa fabricius and the percentage of lymphocytes were measured for a period of 42 days and the data were analyzed. The results indicated that the rate of antibody has significantly [p<0.05] increased with an increase in the amount of propolis in diets and with the levels of 250 mg/kg ration the antibody rose to 10.42 titre at the age of 42 compare to control [6.42]. The weight of thymus gland also increased significantly [p<0.05] with the increase in the levels of propolis and at the levels of 250 mg/kg in ration, weight of thymus increased up to 14.54g in compared to control [8.47 g]. Similarly the weight of bursa fabricius significantly increased [p<0.05] from 2.42 g in contral to 4.62 g in 250 mg propolis/kg of ration [p<0.05]. Intake of 200 and 250 mg propolis/kg of ration has significantly increased the lymphocytes to the levels of 50.18 and 51.25 percent compared to the control [48.93%], respectively. Results indicate that the efficiency of immune-system for immunizing of broiler chickens against Newcastle virus has been promoted using 50 up to 250 mg of propolis per kg of ration