1- Effect of Foeniculi aetheroleum essential oil (EO) on growth performance, nutrient utilization, serum biochemistry, immune response, ileum morphology, microbial population, and meat quality of broiler chickens fed corn- or wheat-based diet were determined. 2- A total of 360 broiler chickens were arranged in a 2×2 factorial assay in a completely randomized design with 6 replicates and 15 birds per experimental unit. Birds were fed corn- or wheat-based diet supplemented with (200 mg/kg) or without fennel EO. 3- Birds fed wheat-based diets had lower BWG and FCR during grower period and lower FI during finisher period as compared to those fed corn-based diet (P < 0.05) whereas addition of fennel EO decreased chickens BWG during finisher period and EPEF, either in wheat or in corn-based diets. Dietary treatments had no effect on serum glucose, triglyceride, cholesterol, LDL-cholesterol, AST, ALT, ALP, and MDA concentrations (P < 0.05). 4- Antibody titers against avian influenza and sheep red blood cell antibody titers, crude protein and crude fat utilization, villous height, crypt depth and epithelium thickness did not influence by dietary treatments (P > 0.05). Inclusion of Fennel EO to corn-based diet resulted in greater villous width and VSA while it reduced lamina propria thickness (P < 0.05). Fennel EO reduced ileal E. coli and lactobacillus bacteria population (P < 0.05). Dietary treatments had no significant effect on meat pH, cooking loss, drip loss, crude protein, crude fat content and cholesterol concentration of breast and thigh meat, total phenolic and MDA concentrations, and breast meat sensory parameters (P > 0.05). 5- These results showed that addition of fennel EO to wheat-based diets had negative effect on chicken growth performance variables and decreased gut E. coli population. While, immunity, meat quality and nutrient utilization were not affected by dietary treatments.
