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Abstract
Three studies were conducted to determine the effects of zinc glycinate on the immune response and growth performance in broiler chickens. The objective of this thesis is to provide insight into the optimal zinc concentration in poultry diets with the focus on supporting the immunity of chickens against diseases. In the first study, broiler chickens were supplemented with two zinc sources, zinc sulfate (ZS) and zinc glycinate (ZG), and three concentrations of supplemental zinc at 40, 80, and 120 mg/kg in a 2 x 3 factorial arrangement. The results indicate that zinc concentration above 120 mg/kg improves the growth performance of broiler chickens and that the growth advantage is accompanied by improvements in intestinal morphology and modulation in immunity through cytokine production. In the second study, broiler chickens were supplemented with 40, 80, and 120 mg/kg of ZG in experiment 1 and supplemented with 100, 120, 140, and 160 mg/kg of ZG in experiment 2. The chickens were experimentally infected with necrotic enteritis by oral gavage of 5,000 oocysts of Eimeria maxima on day 14 and 108 CFU of Clostridium perfringens on day 19, 20, and 21. The results indicate that the alleviation of necrotic enteritis in chickens by ZG at 120 mg/kg was not mediated through the adaptive immunity. In the third study, the effects of zinc on Clostridium perfringens, chicken intestinal cells, and chicken macrophages (HD-11) were investigated in vitro. The results indicate that zinc concentration at 100 μM is beneficial to chicken intestinal cells and macrophages regardless of the zinc source. Taken together, zinc concentration in broiler chicken diets should be supplementaed at 120 mg/kg, and the inclusion of zinc at 100 μM is beneficial to ensure the viability of the cells.