Comparison of two diet types in the estimation of true digestibility of phosphorus in soybean and canola meals for growing pigs by the regression method

Abstract

Two experiments were conducted to compare 2 types of basal diet (semi-purified cornstarch diet and corn-based practical diet) in the determination of true P digestibility (TPD) in soybean (SBM) and canola (CM) meals for growing pigs by the regression method. In each study, forty-eight 25-kg barrows were assigned to 6 dietary treatments arranged in a 2×3 factorial of 2 types of diet (semi-purified cornstarch diet or corn-based practical diet), and 3 graded levels of SBM (Exp. 1) or CM (Exp. 2) at 120, 240, or 360g/kg. Both experiments consisted of a 5-d adjustment period and a 7-d total collection period with ferric oxide used as a marker to indicate the initiation and termination of fecal collection. Our results showed that dietary P intake, fecal P output, digested P, and retained P were increased linearly with graded increasing levels of SBM or CM for growing pigs in each type of diet (P<0.01). Regression of digested P against dietary P intake resulted in the estimated TPD in SBM for pigs fed the semi-purified cornstarch diet and the corn-based practical diet to be 40.01 and 37.49%, respectively. The respective estimates of TPD in CM were calculated to be 30.19 and 27.22% for pigs fed the semi-purified diet and the practical diet. There was no difference in the estimates of TPD in SBM and CM between pigs fed the semi-purified diet and the practical diet. In summary, our data indicated that diet type (semi-purified or practical diet) does not influence the determination of TPD in assay ingredients for growing pigs by the regression method. Therefore, a semi-purified cornstarch diet can be used for determination of P digestibility.