Objective: To evaluate the effect of dietary supplementation of essential oils (EOs) of thyme, clove, and cinnamon to broiler chickens on growth performance, serum metabolites, and tissue lipid peroxidation and antioxidants enzyme activities.
Design: Randomized controlled study
Animals: One hundred-eighty, one-day-old Cobb broiler chicks were randomly allocated into 4 treatment groups (3 replicates, 15 chicks each). Broilers were reared in deep litter system - pens for 6 weeks of age.
Procedures: The control group was fed on corn-soybean basal control diets (starter, grower and finisher) without EOs supplementation. In addition to the basal- control diets, the 3 experimental broiler groups were supplemented with thyme oil (2^nd group), clove oil (3^rd group) or cinnamon oil (4^th group) at 100 mg/kg. Blood, liver and muscle (breast) samples were collected from 3 broilers of each replicate at 40 days of age for measurement of serum metabolites, malondialdehyde (MDA), and antioxidant enzyme activities (liver catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px).
Results: The broiler chickens fed on the diets supplemented with 100 mg/kg cinnamon oil had significantly higher body weight, body weight gain and feed intake, followed by broiler chickens fed on the diets supplemented with 100 mg/kg thyme and 100 mg/kg clove oils in comparison with control group, which was showed the lowest growth performance. Supplementation with EOs significantly improved feed conversion ratio (FCR), with increased liver CAT, SOD, GSH-Px activities, as well as serum level of high density lipoprotein (HDL) in comparison with control group, also, it induced  a significant decrease in serum levels of cholesterol, triglycerides, low density lipoprotein (LDL), as well as both liver and muscle tissue lipid peroxidation (MDA).
Conclusion and clinical relevance: The present results indicate that  dietary supplementation of EOs (thyme, clove, and cinnamon) at 100 mg/kg resulted in significantly higher body weight, body weight gain, improved FCR, reduced serum cholesterol, triglycerides and LDL. Also, reduced lipid peroxidation in liver and muscle, and improved antioxidants status of broiler chickens.