الفهرس 
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Abstract
Tow completely randomized design experiments were simultaneously conducted to evaluate the influence of zinc supplementation on growth performance, carcass traits, some blood parameters, digestibility coefficients for nutrients and economical evaluation of Hubbard broiler chicks under Egyptian summer conditions. A total number of 270 unsexed one week old Hubbard broiler chicks were randomly distributed into nine treatment groups of 30 chicks each with 3 replicates each of 10 chicks. One control was the Zn-unsupplemented basal diet. The added 4 levels of Zn were 20, 40, 60 and 80 mg/ kg diet from either Zn methionine as an organic Zn (experiment 1) or ZnO as inorganic Zn (experiment 2).
Results obtained showed that body weight increased by 2.64, 8.24, 9.19 and 14.56 % in broiler chicks fed diet supplemented with 20, 40, 60 and 80 mg organic zinc/ kg diet, respectively compared with control (unsupplemented) at 5 weeks of age. It could be noticed that chicks fed diet supplemented with 80 mg organic zinc/kg diet recorded the highest feed intake value, while chicks fed unsupplemented diet recorded the lowest value of feed intake. During the whole experimental period (1-5 weeks of age) feed conversion values were improved by 5.12, 6.05, 6.51 and 7.91% in chicks fed diet supplemented with 20, 40, 60 and 80 mg organic zinc/kg diet, respictively when compared with control. The lowest value of feed cost/kg gain and the economical efficiency value were observed for birds fed on diet supplemented with 80 mg organic zinc/kg diet. Inorganic ZnO supplementation had no significant effect on body weight or body weight gain at 3 weeks of age, while there were significant effects at 5 weeks of age. It could be noticed that the highest values of daily body weight gain were recorded by chicks fed diet supplemented with 60 mg ZnO/ kg diet, while the lowest values were recorded by chicks fed control diet. Feed intake and conversion ratio was not influenced by addition of increasing levels of dietary inorganic zinc (ZnO). The lowest value of feed cost/kg gain and the economical efficiency value were observed for birds fed on diet supplemented with 60 mg ZnO/kg diet. In conclusion, the results of this study indicated that, through the hot summer of Egypt, the best performance could be obtained by supplementing 80 mg Organic zinc/kg diet as organic source or 60 mg Zinc oxide/kg diet as inorganic source.