Digestibility of nutrients in growing-finishing pigs is affected by Aspergillus niger phytase, phytate and lactic acid levels. 2. Apparent total tract digestibility of phosphorus, calcium and magnesium and ileal degradation of phytic acid

In growing-finishing pigs, the effects of supplemental microbial phytase, lactic acid and Na phytate in a maize-soybean meal based diet on the apparent total tract digestibility (ATTD) of ash, total P, Ca and Mg and the ileal degradation (AID) of phytic acid were studied. The experimental design was a 2 x 2 x 2 factorial arrangement plus a positive control treatment. Six crossbred castrates of 37 kg initial BW, fitted with steered ileo-caecal valve cannulas were used during six collection periods. The dietary treatments consisted of Aspergillus niger phytase (Natuphos®; 0 or 900 FTU kg-1), sodium phytate (0 or 1.5 g P kg-1) or lactic acid (0 or 30 g kg-1). The positive control diet was supplemented with 1.0 g P kg-1 from monocalcium phosphate monohydrate (MCP). The feeding level was 2.3 times maintenance requirement for energy (418 kJ MEW-0.75). Estimates of AID and ATTD were calculated using Cr2O3 as a marker. The addition of MCP to the diet as the only Variable had no effect on the AID of phytic acid and the ATTD of ash, Ca and Mg, but enhanced total P ATTD. Both microbial phytase and lactic acid enhanced the ATTD of ash, Ca and Mg and the AID of phytic acid, but there was no interaction. The ATTD of total P was increased by the combination of microbial phytase and lactic acid to a greater extent than was calculated as the sum of the stimulatory effects of the single additions. It is hypothesized that lactic acid delays gastric emptying, which prolongs the action of phytase in the stomach at its optimum pH. When Na phytate was added to the diets, total P ATTD was enhanced, possibly reflecting efficient phytate hydrolysis by intrinsic phytase