This study was conducted on 400 one day-old male (Ross 308) broilers to evaluate the effect of Aromabiotic(r) MCFA, at rate of 0.15% in broiler basal diet along with different vaccination methods against ND, and the interaction of these two factors. Chicks equally randomly divided in to 2 main groups, the 1st main group was feeding MCFA at the rate of 0.15% in broiler basal diet which was divided into four subgroups. Three subgroups were vaccinated in different routes with ND and positive control. The 2nd main group was feeding without MCFA (basal diet) and divided to 3 subgroups vaccinated...