Reevaluation of nonphytate phosphorus requirement of growing pullets with and without phytase

An experiment was conducted to re-evaluate the nonphytate phosphorus (NPP) requirement of growing pullets and to determine to what extent this requirement could be reduced by phytase. Six diets in a 3 x 2 factorial design were used. The pullets of the control group (T1) were fed a sequence of 0.4-0.35-0.3% NPP for the age periods of 0 to 6, 6 to 12, and 12 to 18 wk, respectively, according to NRC (1994) recommendation. The NPP level was reduced by an increment of 0.1% in each phase in T2 and T3. The pullets of T4 to T6 were fed similar NPP levels to T1 to T3, respectively, with 300 units phytase/kg diet. From 18 to 30 wk of age, the pullets on all growing regimens were fed a layer diet with 0.4% NPP. Records were maintained for BW and feed intake during the growing period and for egg production during the laying period. Blood and tibia samples were taken at 6, 12, and 18 wk of age for determining plasma P, tibia weight, and tibia ash. Two digestion trials were conducted at Weeks 5 and 18 for determining total P excretion. Body weights at 18 wk and feed intake for the period of 0 to 18 wk were not different from the control for pullets fed the two lower NPP regimens (P > 0.05). Phytase had a favorable effect on BW at 18 wk (P = 0.0539) and feed intake for the period of 0 to 18 wk (P < 0.05). Plasma P was lower for pullets fed the least NPP than for those fed the control NPP regimen only at 6 wk of age (P < 0.05). Bone quality measurements at 6, 12, and 18 wk of age were not different for pullets fed various NPP regimens (P > 0.05). Phytase, for the most part did, not have an effect on plasma P and bone quality (P > 0.05). Total P intake and total P excretion (mg/bird per day) were reduced due to lowering the dietary NPP in both digestion trials (P < 0.05). Phytase did not have an effect on daily total P intake or excretion. Production and specific gravity were not influenced by NPP regimens used during the growing period. Specific gravity for the entire experiment was greater for pullets fed phytase (P < 0.05). The results indicated that the lowest NPP regimen in the absence of phytase was adequate to support performance of pullets, and due to this, it was not possible to determine the effect of phytase in diminishing the P need of growing pullets.