An experiment was conducted to determine and compare the differences in some bone parameters and nutrient excretion and retention of broiler chicks fed 6 different dietary calcium (Ca) and phosphorus (P) levels with or without phytase in factorial design (6×2). A total of 360 one day-old Cobb 500 broiler were assigned to 12 dietary treatments with 3 replicates cages of 10 birds each in factorial design with 6 dietary calcium and Phosphorus levels with or without phytase. Mash diets were corn and soybean-meal based and fed ad-libitum up to 42 days of age. At the end of experiment 6 birds per treatments were slaughtered, lift tibia excised and tibia parameters, (tibia length, width, breaking strength, seedor index, ash%, Ca% and P%) were measurements. The mineral content of calcium and phosphors in feed and excreta were determined and retention of mineral was calculated. The results indicated that:

Different dietary treatments and adding phytase failed to be significant effect on all tibia measurements except tibia breaking strength.
Different dietary treatments and adding phytase had significant effects on tibia ash%
Tibia Ca and P percentages significant affected by dietary treatments
Ca and P execration and retention significantly affected by different dietary treatments

In conclusion, decreasing Ca and P% in the treatments diets didn't affected tibia measurements except tibia breathing strength and decreasing percentages of Ca and P excretion either with or without phytase which retention on enhancement Ca and P retention values.