It was performed three trials to determine the nutritional levels of available phosphorus (aP) for males and females of the strain ISA Label in the starter (1 to 28 days), growing (28 to 56 days) and finisher (56 to 84 days) phases, reared in a free-range system. In each trial, 480 birds with age corresponding to rearing phase were housed in 24 experimental units with shelter and pasture areas. It was used a complete random experimental design, in a 4 × 2 factorial scheme (levels of aP and sexes) with three replicates of 20 birds. The levels of aP evaluated were the following: 0.25, 0.36, 0.47 and 0.58% in the starter phase; 0.18, 0.31, 0.44 and 0.57% in the growing phase; and 0.14, 0.27, 0.40 and 0.53% in the finisher phase. Body weight gain, feed intake, aP intake, feed conversion, contents of phosphorus, calcium and ash in the tibia and bone breaking strength were evaluated. According to results, the optimum dietary aP levels in the starter phase, for males and females, are 0.39 and 0.49%, which correspond to the intake of 3.94 and 3.96 g of aP/bird, respectively. For the growing phase, it is recommended 0.35% of aP in the diet for birds of both sexes, which correspond to an intake of 8.45 and 6.70 g of aP/bird. In the finisher phase, it is recommended the levels 0.32 and 0.30% of aP, which corresponds to intakes of 12 g and 9.5 g aP/bird for males and females, respectively.
bones; calcium; slow-growing birds
