Five hundred day-old male Ross broiler chicks were divided into 50 groups of 10 birds each and randomly assigned to 10 dietary treatments with 5 replicates each. Two corn-soybean meal-based diets were first provided to meet 100% and 95% of recommended digestible amino acids (RDAA) for starter (1–14 d), grower (15–35 d) and/or finisher (36–49 d) periods. Each starter diet was subdivided into 5 parts and supplemented with 0 and 2 g/kg Fermacto and 0.2, 0.4 and 0.8 g/kg cumin essential oil (CEO). The grower diets contained half of the same supplementation in the starter diets and each of the un-supplemented finisher diet was fed to the corresponding birds. The performance parameters were determined during all periods and carcass yields and relative organ weights measured on d 28 and 49. The blood metabolites, cell differentiation and total anti-SRBC, IgG and IgM titers measured on d 26 in birds fed 100% RDAA diets. The CEO and Fermacto did not have a significant effect (P > 0.05) on performance in the starter and finisher periods but higher BWG was observed in birds fed diet with the lowest level of CEO in the grower period. Birds fed diet with 100% RDAA and Fermacto had higher feed: gain ratio in the growing period compared with those fed diet of similar AA and 0.2 g/kg of CEO. A 5% decrease in the RDAA had no adverse effect (P > 0.05) on the overall FI and BWG, but FCR was increased (P > 0.05). Carcass yields and cuts were not influenced (P > 0.05) by CEO, Fermacto or DAA levels. There was not a signifi- cant difference (P > 0.05) in total anti SRBC, IgG and IgM titers The inclusion of Fermacto or various levels of CEO in diets did not affect (P > 0.05) serum metabolite (mg/dL) at d 28, although triglyceride and VLDL concentrations was lower (P < 0.05) in chicks fed starter diet contained 0.4 g/kg CEO.

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