Abstract :

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roduction performance is closely related to feed intake and feed components. Heat stress has a direct effect on feed intake and can impair productivity and immunological responses. The present study was designed to investigate the effect of feed restriction and vitamin C supplementation on broiler performance under heat stress conditions. A total of 180 one-day old Arbor Acres chicks were randomly assigned to four experimental groups with three replicates (15 birds of each). The experimental chicks were fed the basal diet ad libitum (Control), fed the basal diet supplemented with 250 mg/kg vitamin C (Vit. C) ad libitum, deprived of feed for 8h/day (FR), or received the basal diet supplemented with 250 mg/kg vitamin C with feed deprivation for 8h/day (FR+Vit. C). All the experimental groups were exposed to cyclic environmental heat stress of 33.5±1.5˚C for 8h/day starting from 21 to 42 days of age. The feed withdrawal was synchronized with the period of temperature elevation. Feed intake, body weight gain and feed conversion were measured on 0, 21, 35 and 42 days of the experiment. At the end of the experiment, blood samples were collected for determining the H/L ratio and quantifying some relative plasma constituents. Antibody titers of Newcastle (ND), Infectious Bronchitis (IBD) and Avian Influenza (AID) diseases were quantified after three weeks of immunization. Data revealed that feed restriction caused a significant reduction in feed intake and weight gain of broilers during the first three weeks of life. Vitamin C supplementation improved feed intake, body weight gain and feed conversion during the period from 22 to 35 days. Plasma total protein and albumin increased significantly, while transaminases (liver enzymes) activity and the H/L ratio were reduced significantly due to different treatments when compared to the control. Antibody titers for ND and IBD significantly increased due to the different treatments as compared to the control group. The data revealed that feed restriction under thermo-neutral condition reduces the broiler growth performance. But when birds were subjected to elevated environmental temperature, feed rustication with or without vitamin C supplementation improved the broiler performance, with no effect on carcass characteristics, and produced a substantial improvement in immune response of heat stressed broilers. Vitamin C supplementation at 250 mg/kg can be used to alleviate the negative effects of heat stress on broiler productive and immunological responses.

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