Key points are not available for this paper at this time.
An experiment employing a factorial arrangement of two levels (3.0 and 4.0%) of Ca, two levels (0.15 and 0.25%) of nonphytate phosphorus (NPP), and two levels (0 and 300 U/kg diet) of microbial phytase was carried out with 960 ISA-brown layers from 21 to 41 wk of age. There was a significant interaction between NPP level and phytase for egg production. High NPP level and phytase supplementation increased egg production only in the second 10-wk period (31 to 41 wk). High NPP and low Ca increased feed intake, and a significant interaction between levels of NPP and Ca was observed in the first 10 wk. High NPP improved feed efficiency only in the second 10-wk period. Low NPP improved egg specific gravity and eggshell thickness but decreased Haugh units in the first 10-wk period; high NPP decreased the percentage of broken and soft-shell eggs in the second period. Low Ca decreased egg specific gravity, eggshell strength, and eggshell thickness in both periods and increased Haugh units in the second 10-wk period. Phytase supplementation decreased the percentage of broken and soft-shell eggs. High NPP increased fiber availability but decreased Ca availability. High Ca decreased Ca availability, whereas phytase increased availability of dry matter, fiber, and P. High NPP increased retention of P and Fe but also increased excretion of P. High Ca decreased retention of Zn and Fe. Phytase supplementation increased P retention, resulting in decrease of P excretion. In conclusion, supplementation of microbial phytase at a level of 300 U per kg diet of laying hens can improve egg production, decrease broken and soft egg production rate, and P excretion. The effects of phytase supplementation are significantly modified by the level of Ca and NPP.
Lim et al. (Wed,) studied this question.