Precise phosphorus nutrition is important for significant reductions in both P pollution and ration costs. The influence of different levels (%) of dietary nPP fed from 0 to 20 d (0.45, 0.40, 0.35, 0.30, 0.25, compared with feeding 0.20 nPP with and without 500 F.T.U. of phytase per kg of diet) and from 21 to 36 d of age (0.414, 0.364, 0.314, 0.264, 0.214, compared with 0.164 nPP with and without 500 F.T.U. of phytase per kg of diet) were evaluate using a total of 588 day-old commercial broiler chicks. Each treatment was replicated four times in a completely randomized design. Body weight (BW), daily gain (DG), feed intake (DFI), feed conversion ratio, plasma P level and bone characteristics were determined, and from these data the P equivalency of the phytase was estimated. Feeding diets containing less than 0.40% of nPP to birds between 0 and 20d resulted in inferior BW, DFI, plasma P level and bone characteristics compared with the control. However, optimum FCR and mortality was supported at lower levels of nPP (0.25%). Between 21 and 36 d, 0.364% was enough to optimise BW, DFI, and femur ash (%); whilst only 0.314% or greater was needed to support optimum DG, toe and tibia ash and only 0.214 to 0.264% was required to optimise shank, femur and tibia lengths; FCR and survivability. A broken line analysis also showed that the nPP (%) requirement ranged from 0.267 to 0.410 and 0.272 to 0.380% during 0 to 20 and 21 to 36 d, respectively. Phytase supplementation improved performance and bone criterion and its P equivalency, depending upon the response of interest and birds age, ranged from 0.00 to 0.110%. In conclusion, the results showed that the combination of a lower level of nPP and phytase may be used to increase dietary P utilization, without severe changes in performance and bone quality.
