The main aim of the current experiment was to assess the potential of dietary orange peel extract (OPE) and lemon peel extract (LPE) as promoters of broiler resistance to high ambient temperature. The experiment was conducted as a 2
3 factorial arrangement of treatments with 2 levels of OPE (0 and 200 mg/kg feed) and 3 levels of LPE (0, 200, and 400 mg/kg feed). At d 25, a total of 288 Ross 308 broilers were randomly assigned to 6 dietary treatments with 4 replicates of 12 broiler chickens each. The temperature was increased to 34 1C with 50% relative humidity for 5 h daily starting from d 28 until d 38. At the end of the trial (d 38), 4 male broiler chickens per pen were sampled for determination of serum components and variables of intestinal morphology. Dietary OPE and LPE did not affect weight gain, feed intake, and feed conversion ratio of broiler chickens. The inclusion of 200 mg/kg OPE increased serum total protein, but reduced serum lactate dehydrogenase and creatine phosphokinase activity in broiler chickens (Po0.05). Lemon peel extract supplementation decreased the activity of lactate dehydrogenase quadratically (P¼0.039) and creatine phosphokinase linearly (P¼0.037). No differences in the other blood characteristics and intestinal traits were observed with the exception of muscularis thickness of duodenum, which was reduced when LPE was added to the diet (linear, P¼0.011). These results indicate that OPE, LPE, and their combinationmightmodify some blood components and the proximal intestinal morphology, but without beneficial effect on growth performance of broiler chickens under hot conditions

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