A total of 450 one-day-old male broiler chickens (Ross 308) were allocated to 9 dietary treatments to evaluate the effects of different sources and contents of Zn and their interaction on growth performance, carcass characteristics, immune responses, and antioxidant activities in broiler chickens reared under high temperature conditions. From d 14 to 42, the average minimum and maximum room temperatures were 27.1 ± 1.8 and 37.9 ± 2.3°C, respectively, with relative humidity ranging from 46 ± 1.4 to 55 ± 2.5%. The experiment consisted of a 3 × 3 factorial arrangement of treatments with 3 sources of dietary Zn [Zn oxide, Zn-Met, and Zn oxide-nanoparticles (ZnO-NP)] and 3 concentrations of supplemental Zn (low: 20 mg/kg, adequate: 40 mg/kg, and high: 80 mg/kg). Each treatment had 5 replicates of 10 broiler chickens per replicate cage. Average daily feed intake, average daily gain (ADG), and feed conversion ratio (FCR) were monitored during the starter (d 0 to 10), grower (d 10 to 24), and finisher (d 24 to 42) periods. On d 42, 2 broiler chickens per replicate were slaughtered to evaluate the carcass-related traits. Blood samples (2 samples per replicate) were taken for measuring antibody responses after challenge with sheep red blood cells (SRBC) on d 21 and 42, and also for antioxidant/oxidant status analysis on d 42. Under heat stress, dietary Zn content did not influence growth performance, but total and IgM antibody titers against SRBC for secondary response were increased (P < 0.05) in broiler chickens receiving high-Zn diets. The ADG from d 0 to 42, relative spleen weight, total and IgG antibody titers against SRBC for primary responses and serum superoxide dismutase activity in the Zn-Met and ZnO-NP treatments were greater (P < 0.05) than those of Zn oxide treatment. Moreover, overall FCR and serum malondialdehyde concentration were decreased by dietary supplementation of Zn-Met and ZnO-NP (P < 0.05). At the high contents of Zn, response to supplemental Zn-Met a
