In performanceand metabolism trials, diets with reduced levels of crude protein, calcium andavailable phosphorus on the performance, carcass characteristics, tibia ashes,balance and retention of nitrogen and phosphorus of broiler chickens in phasefrom 8 to 21 and 8 to 35 days were evaluated. In each phase, 30 and 25 birdsper experimental unit were used in the performance assay and five and threein the metabolism assay, respectively, in a completely randomized experimentaldesign, with six replications. Treatments consisted of diet with 21% crude proteinwithout phytase (control), formulated with nutritional levels recommended onthe Brazilian tables, and diets with 21, 20, 19 and 18% crude protein with phytase(8 to 21 days) and from 8 to 35 days, the control diet had 20% crude proteinwithout phytase (control), and others diets with 20, 19, 18, 17% crude protein,with phytase. In the diets with phytase (80 g of Ronozyme NP(M) phytase perton of diet), the level of available phosphorus was reduced in 0.15 and thecalcium in 0.30 percentage points in relation to the control diet. No effectwas observed with the reduction of nutrients on feed intake, weight gain, orfeed conversion in either phase or for the study of carcass characteristicsto the 35 days. However, higher abdominal fat percentage was observed when thebroilers were fed diet with lower protein level. The excretion of nitrogen andphosphorus decreased when birds received diets with reduced levels of thesenutrients. Ash percentage in the tibia was not influenced by treatments. Itis possible to reduce protein level, available phosphorus, and calcium of thediets in up to 3, 0.15 and 0.30 percentage points when the diets are supplementedwith phytase and amino acids, respectively.
