الفهرس 
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Abstract
This work was carried out to study the effect of calcium, available phosphorus and microbial phytase supplementation on growth performance and carcass traits of broiler chicks. A 3×2×2 factorial design experiment was performed including three levels of calcium (0.75, 1.00 and 1.25%), two levels of available phosphorus (0.2 and 0.4%) and two levels of microbial phytase (0 and 500 FTU/Kg diet) through 1-6 wks of the age. A total number of 360 Hubbard broiler chicks were randomly divided into 12 treatment groups, each of 30 chicks (3 replicates / 10 chicks). The results obtained could be summarized as follow: final body weight and body weight gain were significantly (P≤0.05) affected by the dietary calcium levels studied in Hubbard broiler diets. The heaviest body weight and body weight gain were recorded by broilers fed 0.4% available phosphorus diet. While the lowest values were recorded for broilers fed the diet contained 0.2% available phosphorus. Live body weight and body weight gain of Hubbard broilers were significantly increased by adding microbial phytase at a level of 500 FTU/kg. Increasing dietary calcium from 0.75 to 1.25% had significantly decreased feed intake during all the experimental periods studied. Daily feed intake was significantly affected by dietary available phosphorus throughout all the experimental periods. Feed intake was significantly (P≤0.01) improved due to microbial phytase addition of the experimental Hubbard broiler diets when compared to those fed unsupplemented one during all the experimental periods. Decreasing dietary calcium level to 0.75% significantly (P≤0.01) improved feed conversion values throughout all the experimental periods. Feed conversion values were significantly improved with increasing dietary available phosphorus level in the diets. Feed conversion values were improved significantly during the whole experimental period in broilers fed diet supplemented with microbial phytase when compared with those fed unsupplemented one. Increasing the level of available phosphorus from 0.2 to 0.4% led to a significant increase in giblets %. Significant influences were observed in all of carcass characteristics studied due to the effect of the tested levels of dietary microbial phytase, except each of feather. In conclusion, the results of this study indicated that, supplementing 500 FTU/Kg phytase to the diets with 1% calcium and 0.4% available phosphorus gave the best performance of Hubbard broiler chicks.