True digestibility of phosphorus in canola and soybean meals for growing pigs: Influence of microbial phytase

Two studies with growing pigs were conducted using the regression analysis technique to estimate the true digestibility of P (TPD) in canola (CM) and soybean (SBM) meals, and quantify the effect of microbial phytase on TPD of CM and SBM. In each study, 48 (Exp. 1) or 36 (Exp. 2) 17-kg barrows were assigned to 6 dietary treatments arranged in a 3 x 2 factorial of 3 graded levels of CM (Exp. 1) or SBM (Exp. 2) at 132, 264, or 396 g/kg, and 2 levels of phytase at 0 or 1,000 units/kg. The total collection method was used to calculate P digestibilities. In Exp. 1, phytase supplementation increased (P < 0.01) the apparent total tract digestibility of P in CM with values ranging from 26 to 33% without phytase and from 57 to 62% with supplemental phytase. Regression of digested P against dietary P intake resulted in a decreased (P < 0.05) TPD estimate of 34.3% for the diet without phytase than the 61.4% TPD estimate for diet with added phytase. In Exp. 2, phytase supplementation improved (P < 0.05) apparent total tract P digestibility for SBM with values ranging from 34.3 to 38.6% without phytase and from 68 to 71.2% with supplemental phytase. True P digestibility estimate for SBM without phytase at 40.9% was different (P < 0.05) from that with added phytase at 70.8%. These results indicate a TPD of 34 or 41% in growing pigs fed CM or SBM and demonstrate that the addition of microbial phytase at 1,000 units/kg improves true digestibility of P in CM and SBM by 78 and 73%, respectively.