Effect of different sources and contents of zinc on growth performance, carcass characteristics, humoral immunity and antioxidant status of broiler chickens exposed to high environmental temperatures

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 14 to 42 days, the average minimum and maximum room temperatures were 271 +/- 1.8 and 37.9 +/- 2.3 degrees C, respectively, with relative humidity ranging from 46 +/- 1.4 to 55 +/- 2.5%. The experiment consisted of a 3 x 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 (0-10 days), grower (10-24 days), and finisher (24-42 days) periods. On day 42, 2 broiler chickens per replicate were slaughtered to evaluate the carcass-related traits. Blood samples (2 samples/replicate) were taken for measuring antibody responses after challenge with sheep red blood cells (SRBC) on days 21 and 42, and also for antioxidant/oxidant status analysis on day 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 0 to 42 days, 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 appears to be increased in terms of relative spleen weight (P = 0.048) and primary anti-SRBC titers of total and IgG antibodies (P = 0.023 and P = 0.018, respectively), resulting in significant Zn source x Zn content interactions. In conclusion, the delivery of Zn in the forms of Zn Met and ZnO NP at concentration of 40 mg/kg of diet could beneficially affect the growth performance, immune response, and antioxidant status of broiler chickens reared under high ambient temperatures.