Influence of feeding level on apparent total tract digestibility of phosphorus and calcium in pigs fed low-phosphorus diets supplemented with microbial or wheat phytase

Eighteen pigs (initial body weight 11.3 kg) were used in a 5-week digestibility experiment to investigate the effects of supplemental microbial and native wheat phytase on apparent total tract digestibility (ATTD) of phosphorus (P) and calcium (Ca) at different feeding levels (FL) in a 3 × 3 factorial arrangement of treatments. A low-P (4.2 or 1.4 g/kg DM total or digestible P, respectively) corn–soybean meal diet, either containing 0 or 550 U/kg from microbial (Penicillium) or wheat phytase, respectively, was fed at three FL (1.2-, 2.0- or 2.8-fold the ME maintenance requirement) in three consecutive periods. Pigs were kept in metabolism crates and feces and urine were quantitatively collected. Supplementation of the control diet with microbial phytase increased (P < 0.001) ATTD of P and Ca by 22.6 and 18.3 percentage units, respectively. Similarly, but to a smaller extent, inclusion of wheat phytase increased ATTD of P (P < 0.001) and Ca (P = 0.005) by 7.4 and 4.9 percentage units, respectively. The overall ATTD of P and Ca were positively influenced by the level of feed intake (P < 0.001). Increasing the FL improved the efficiency of microbial phytase (P < 0.05) but not of wheat phytase (P > 0.05) in rendering phytate P digestible. Phytase effects on ATTD of Ca were not affected (P > 0.05) by an increase in FL.