The objective of this experiment was to test the hypothesis that addition of microbial phytase to soybean meal (SBM) will result in increased standardized total tract digestibility (STTD) of P and increased plasma inositol in growing pigs. Twenty diets were arranged in a 4 × 5 factorial with four sources of SBM (i.e., sources 1, 2, 3, and 4) and five levels of supplemental phytase (i.e., 0, 500, 1,000, 2,000, and 4,000 units/kg diet). In all diets, SBM was the only source of phytate and P. All diets contained all nutrients except P and Ca at or above the requirements for pigs. A total of 160 pigs (initial weight: 15.81 ± 2.69) were allotted to one of the 20 diets using a randomized complete block design with four blocks of 40 pigs for a total of eight replicate pigs per diet. Pigs were housed individually in metabolism crates that allowed for total, but separate, collection of feces and urine. Pigs were fed experimental diets for 18 days with the first 10 days considered the adaptation period. On day 18, a blood sample was collected from the jugular vein of all pigs. The apparent total tract digestibility (ATTD) and STTD of P in each diet were calculated. Deproteinated plasma samples were analyzed for myo-inositol concentration. Data were analyzed using the PROC MIXED procedure of SAS. Pig was the experimental unit. Results were considered significant at P ≤ 0.05 and 0.05 ≤ P < 0.10 was considered a tendency. Fixed effects included SBM source, phytase, and the interaction between SBM source and phytase, and block and replicate within block were random effects. There were no interactions between phytase and source of SBM for ATTD of P, STTD of P, P retention, or plasma inositol concentration. Therefore, polynomial contrasts were used to test for linear and quadratic effects of increasing levels of phytase, using phytase level as the main effect. The ATTD and STTD of P, P retention, and plasma inositol increased (quadratic, P < 0.05) as the inclusion of phytase increased in diets (Table 1). The observed increase in plasma inositol indicates degradation of phytate in the intestinal tract and inositol absorption. Increased circulating inositol may enhance insulin sensitivity, glucose and lipid metabolism, and cellular osmotic balance, which may contribute to a potential extra-phosphoric effect of phytase supplementation beyond improved P utilization. In conclusion, phytase improved P digestibility, retention, and plasma inositol concentration regardless of SBM source, enhancing nutrient utilization from phytate.

Ortiz, A. S. Lee and H. Stein. 2026. Release of Phosphorus and Inositol from Soybean Meal by Growing Pigs Fed Diets with Graded Levels of Microbial Phytase. ASAS Midwest Section Meeting. Abstract 163. https://doi.org/10.1093/jas/skag107.158