الفهرس 
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Abstract
A total of 80 broiler chicks were used in this experiment which extended for 6 weeks and the feeding period was divided into 3 stages: 1) Starter stage: from 0-14 day in which the bird fed diet containing CP23.01 % and ME 3003 kcal/kg diet. 2) Grower stage: from 15-28 day in which the bird fed diet containing CP 21.51% and ME 3102 kcal/kg diet. br>3) Finisher stage: from 29-42 day in which the bird fed diet containing CP 20.24% and ME 3203 kcal/kg diet. The experiment design was as the following: Basal standard diet without additives, basal standard diet with 500 gm/ton B-mannanase, basal standard diet with 69 kcal/kg less energy content without additives and basal standard diet with 69kcal /kg less energy content with 500 gm/ton B-mannanase. The birds were weighed individually at the beginning of the experiment then body weight and feed intake was recorded every week for each group. Blood samples were collected into clean centrifuge tube without anticoagulant at 22, 28, 35 day for HA and HI determination. At the end of the experiment period (42days), 4birds from each group were randomly selected and slaughtered for studying carcass traits (estimating dressing% and weight of intestinal tracts, liver, heart, spleen, bursa and gizzard) and blood samples collection as samples were collected into clean centrifuge tube with EDTA for total leukocytic count. Samples of intestinal tract (duodenum) were collected from each slaughtered bird for measuring crypt depth and height of villi. Samples of digesta were collected from jejunum of each slaughtered bird for measuring the viscosity. Samples of dropping were collected for measuring the digestibility.