The effect of a dietary microbial phytase on mineral digestibility throughout the gastrointestinal tract of the growing pig was studied. Thirty-two male pigs weighing about 22 kg were allocated equally to four corn–soybean meal diets. One diet was adequate in total phosphorus (P) and calcium, (Ca), the second diet was deficient in total P and Ca (low-P diet), and the third and fourth diets were the low-P diet with microbial phytase added at 1,107 U/kg or 2,215 U/kg, respectively. Titanium dioxide was included in the diets as an indigestible marker. The pigs were fed their respective diets for 42 days. Fecal samples were collected from day 38 to 41 and stomach chyme, terminal jejunal, and terminal ileal digesta samples were collected after euthanasia on day 42. Phytate P degradability and apparent total P and Ca digestibility were determined at the gastric, jejunal, ileal, and total tract levels.

Phytate P degradation and apparent total P and Ca digestibility were not significantly different between the two microbial phytase inclusion levels. Across both microbial phytase-low-P diets, phytase supplementation increased (P < 0.05) phytate P degradability at the jejunal, ileal, and total tract levels by 101%, 77%, and 10%, respectively, but not at the gastric level. Total tract phytate P degradation was greater (P < 0.05) than ileal phytate P degradation for both the unsupplemented (52% units greater) and phytase-supplemented, low-P (26% units greater) diets. The latter result was not reflected by the apparent total P digestibility estimate, which was not significantly different between the ileal and total tract levels for both the unsupplemented and phytase-supplemented, low-P diets. Consequently, there appeared to be considerable phytate degradation in the hindgut, presumably due to the action of hindgut microbes, but the phytate P released in the hindgut did not appear to be absorbed. Apparent Ca digestibility was not significantly different among jejunal, ileal, and total tract levels for any of the dietary treatments, but apparent Ca digestibility was greater (P < 0.05) for the phytase-supplemented diets compared with the unsupplemented diets. Overall, dietary microbial phytase supplementation led to greater phytate degradation to the end of the jejunum. Because the phytate P released in the hindgut was not absorbed, ileal estimates, rather than total tract estimates, of phytate degradation appear to more accurately reflect P availability.