Non-phytate phosphorus concentration in the pre-experimental starter period impacts broiler tibia mineralization response to phytase supplementation

The non-phytate phosphorus (nPP) concentration in the diet fed during the starter period can impact bone formation, and phosphorus digestibility in the following phase, which may influence the effectiveness of phytase supplementation. To investigate the impact of nPP concentration in the starter diet on response to phytase in the subsequent period, an experiment was conducted in a 2 × 3 split-plot design, consisting of 2 starter diets with 3 or 4.5 g/kg of nPP (24 replicates with 8 birds per cage), and 3 grower diets with increasing doses of phytase (0, 1,000 or 2,000 FYT/kg) with 8 replicates and 6 birds per cage. Starter diets were fed for the first 11 d post hatching. On d 11, birds were selected to maintain the ratio of BW between the two starter diets, and allotted to the grower diets for the subsequent 11 d. On d 22 post hatching, birds were euthanized to collect ileal digesta and tibia samples. Data was analyzed as a randomized complete block in a split-plot design to determine the effect of starter and grower diets and their interaction. Birds fed adequate nPP during the starter period had greater (P < 0.05) tibia breaking strength and tibia weight, and lower (P < 0.05) calcium and dry matter ileal digestibility, and tended to have lower phosphorus digestibility (P = 0.088). Phytase supplementation led to greater (P < 0.05) phosphorus digestibility, feed efficiency, tibia weight, Ca in tibia, and breaking strength regardless of the starter diet. An interaction between the level of nPP in the starter diet and grower diet phytase supplementation was noted (P < 0.05) for tibia ash weight and concentration, and a tendency (P = 0.073) for phosphorus in tibia, where phytase supplementation led to a greater response in birds fed the low nPP starter diet. In conclusion, the starter diet nPP concentration did not influence phytase efficacy in enhancing phosphorus digestibility or performance during the grower period but did affect tibia ash.