Nonphytate phosphorus requirement of laying hens with and without phytase on a phase feeding program

An experiment was conducted to reevaluate the nonphytate P (NPP) requirement of laying hens with and without phytase. The experiment involved 12 treatments in a 6 x 2 factorial design. The hens of the control group (T1) were fed a sequence of 0.40-0.35-0.30% NPP during 30 to 42, 42 to 54, and 54 to 66 wk, respectively. The NPP was reduced in increments of 0.05% in T2 to T6. The hens of T7 to T12 were fed NPP regimens similar to T1 to T6 but with 300 units phytase/kg diet. Two digestion trials were conducted during 42 and 66 wk, and nitrogen, phytate, and total P retention were determined. In the absence of phytase, production traits were not different for hens fed a NPP regimen of 0.25-0.20-0.15% than for the unsupplemented phytase control group for the entire experiment (P > 0.05). However, production traits were inferior for hens fed the lower NPP regimens (P < 0.05). In the presence of phytase, production traits were not different for hens fed the lowest NPP regimen (0.15-0.10-0.10%) than for the unsupplemented phytase control for the entire experiment (P > 0.05). The overall effect of NPP regimens and phytase on specific gravity for the entire experiment was significant. Specific gravity was greater for hens fed the regimens with less NPP than for hens fed regimens with greater NPP, and phytase had an adverse effect on specific gravity. However, specific gravity of hens fed the lowest NPP regimen with phytase was not significantly different from the unsupplemented phytase control group. The overall effect of phytase on phytate P retention was significant during digestion trials; phytase increased phytate P retention by about 15%. Daily total P excretion was 34 to 47% less for hens fed the lowest NPP regimen with phytase than for the unsupplemented phytase control group. Significant interactions existed for a number of traits and are discussed in the text.