The objective was to evaluate the effect of microbial phytase (1250 FTU/kg diet with 88% dry matter (DM)) on apparent total tract digestibility (ATTD) of phosphorus (P) in pigs fed a dry or soaked diet. Twenty-four pigs (65 +/- 3 kg) from six litters were used. Pigs were housed in metabolism crates and fed one of four diets for 12 days; 5 days for adaptation and 7 days for total, but separate collection of feces and urine. The basal diet was composed of wheat, barley, maize, soybean meal and no mineral phosphate. Dietary treatments were: basal dry-fed diet (BDD), BDD with microbial phytase (BDD + phy), BDD soaked for 24 h at 20 degrees C before feeding (BDS) and BDS with microbial phytase (BDS + phy). Supplementation of microbial phytase increased ATTD of DM and crude protein (N x 6.25) by 2 and 3 percentage units (P < 0.0001; P < 0.001), respectively. The ATTD of P was affected by the interaction between microbial phytase and soaking (P = 0.02). This was due to a greater increase in ATTD of P by soaking of the diet containing solely plant phytase compared with the diet supplemented with microbial phytase: 35%, 65%, 44% and 68% for BDD, BDD + phy, BSD and BSD + phy, respectively. As such, supplementation of microbial phytase increased ATTD of P in the dry-fed diet, but not in the soaked diet. The higher ATTD of P for BDS compared with BDD resulted from the degradation of 54% of the phytate in BDS by wheat and barley phytases during soaking. On the other hand, soaking of BDS + phy did not increase ATTD of P significantly compared with BDD + phy despite that 76% of the phytate in BDS + phy was degraded before feeding. In conclusion, soaking of BDS containing solely plant phytase provided a great potential for increasing ATTD of P. However, this potential was not present when microbial phytase (1250 FTU/kg diet) was supplemented, most likely because soaking of BDS + phy for 24 h at 20 degrees C did not result in a complete degradation of phytate before feeding.
