الفهرس 
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Abstract
This study was conducted at the poultry production station. Faculty of Agriculture , Mansoura University. The objectives of the study were to investigate the effects of feeding rations of different dietary protein levels, with almost constant energy content, on the performance of Dokki-4(D4) and Rhode Island Red (RIR) chickens during the growing period from 10 up to 20 weeks of age. A- Starting Period: The chicks were fed a starter rat ion from one-day old up to 8 weeks of age and a grower ration from 8 up to 10 weeks of age . During this period, data on body weight , weight gain, feed consumption and feed conversion were recorded B-Growing Period : (from 10 up to 20 weeks of age) The feed was changes to the experimental die t s which contained different protein levels of 11,1 4 ,17 a nd 20\ with almost constant energy content of about 2886 kcal/kg. ME. A commercial grower ration which contained about 15.5\ crud e protein and about 2880 Kcal/ kg; ME was also used and served as a reference diet. Each diet was fed to three replicates of 20 chicks each (in both the two ” breeds ). During this period , body weight. growth rate, feed consumption, and feed conversion were recorded.