An experiment was conducted to test the hypothesis that the apparent total tract digestibility (ATTD) and the standardized total tract digestibility (STTD) of phosphorus in fermented soybean meal (FSBM) are greater than in conventional soybean meal (SBM) when fed to growing pigs. Four diets were formulated to contain FSBM or SBM-CV and either 0 or 800 units/kg of microbial phytase. The only sources of phosphorus in these diets were FSBM and SBM. A phosphorus-free diet to estimate basal endogenous losses of phosphorus was also formulated. Thirty barrows weighing about 14kg were allotted to five diets in a randomized complete block design with six pigs per diet. Feces were collected for five days after a five-day adaptation period. All samples of ingredients, diets, and feces were analyzed for phosphorus and values for ATTD and STTD of phosphorus were calculated.

Results indicated that the basal endogenous phosphorus losses were 187 mg/kg of DMI. As phytase was added to the diet, the ATTD and STTD of phosphorus increased (P < 0.01) from 60.9 to 67.5% and from 65.5 to 71.9%, respectively, in pigs fed FSMB. Likewise, addition of phytase to SBM diet increased (P < 0.01) the ATTD and STTD of phosphorus from 41.6 to 66.2% and from 46.1 to 71.4%, respectively. The ATTD and STTD of phosphorus were greater (P < 0.01) in FSBM than in SBM diet when no phytase was used, but that was not observed when phytase was added to the diet (soybean meal × phytase interaction, P < 0.01). In conclusion, the ATTD and STTD of phosphorus in FSBM was greater than SBM when no microbial phytase was added, but when phytase was added to the diets, no differences between FSBM and SBM were observed in the ATTD and STTD of phosphorus.