The negative effects of high ambient temperature during some months of the year on poultry production has been of great concern in many countries. Dietary modifications are among the most practical ways to alleviate the effects of high temperature. Possible effects of dietary supplementation with 200 or 400 mg/kg feed of lemon peel extract (LPE), orange peel extract (OPE) and Curcuma xanthorrhiza essential oil (CXEO) under hot conditions (34°C with 50% relative humidity for 5 h daily starting from d 28 until d 38 of age), on blood antioxidant enzyme activities, biochemical parameters and antibody titers of broiler chickens were investigated. All extracts are rich in phenolic compounds and highly available. Compared to control, supplementation with OPE at 400 mg/kg and CXEO significantly increased erythrocyte glutathione peroxidase and superoxide dismutase activity, plasma growth hormone concentrations and serum phosphorus, total proteinand chloride concentrations and decreasedserum LDL and cholesterol concentrations in chickens at 38 d of age. Regarding antibody titers, CXEO supplementation at 400 mg/kg caused a significant increase in Bronchitis antibody titers. Supplementation with LPE and OPE gave more inconsistent results. Most interesting, 400 mg/kg LPE significantly increased 3,5,3′-triiodothyronine and growth hormone concentration as compared to the control. In conclusion, the herbal extracts tested in this study, in particular CXEO at 400 mg/kg, may relieve some of the changes in blood composition induced by elevated ambient temperatures.

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