In order to determine, the effects of adding different levels Satureja khuzistanica essential oil in two common and microcapsulated forms to diet on performance, immune response, blood biochemical parameters and intestinal morphology of broiler chickens, an exprement was conducted using 400 Ross 308 (mixed sex) broiler chickens, in five treatments, four replicates and 20 chickens per each replicate were used in completely randomized design. Treatments were included: control (no additive), dietary containing levels of 400 and 500 mg/kg Satureja essential oil and dietary containing levels of half and one percent capsulated Satureja essential oil. Adding different levels of Satureja khuzistanica essential oil in two common and microcapsulated forms to diet of broiler chickens had no effect on feed intake and FCR, immune response and the number of white and red blood cells. But, experimental treatments containing common and microcapsulated Satureja essential oil than the control caused a significant decrease the body weight of the birds. The level of thyroid hormones (T3 and T4) and blood biochemical parameters (cholesterol, triglyceride, HDL and LDL) were not affected by the experimental treatments. Although small intestin histologhy traits like width of villi, depth of crypt and length of villi to depth of crypt ratio were not affected by the experimental treatments, but level of half percent of capsulated Satureja essential oil caused a significant decrease length to width of villi ratio (P<0/05). Acccording to the results of the present experiment, using of Satureja essential oil in two common and capsulated forms in the levels used in this study is not recommended.

Keywords: Blood Biochemical Parameters, Broiler Chicken, Cell Count, Intestinal Histology, Satureja Essential Oil.