Phytate, derived from plant-sourced feed ingredients, is invariably present in practical pig and poultry diets. Phytate-degrading feed enzymes have been included in monogastric diets for more than fifteen years and this is an increasingly common practice. Notionally, microbial phytase has the capacity to hydrolyse dietary phytate, the mixed salt of phytic acid (myo-inositol hexaphosphate; IP6) to liberate six P moieties and inositol in the porcine gastrointestinal tract. In practice, however, only a proportion of phytate-bound P is released because phytase does not degrade phytate completely (Kemme et al., 2006). Nevertheless, as initially demonstrated by Simons et al. (1990), phytase enhances P digestibility and reduces P excretion. In 60 kg pigs, these researchers reported that Aspergillus niger phytase inclusion in maize–soy diets containing approximately 3.2 g kg− 1 phytate-P increased P digestibility by a factor of 2.3 (0.46 versus 0.20) and reduced P excretion by 35% (13.6 versus 21.0 g kg− 1 DM faecal P). Numerous subsequent reports have confirmed the capacity of microbial phytases to increase P digestibility and reduce P excretion in pigs.