PSI-11 - Determination of standardized total tract phosphorus digestibility in expeller-pressed Canadian prairie grown soybean meal fed to growing pigs

Abstract: The objectives of this study were 1) to determine the apparent total tract digestibility (ATTD) of calcium (Ca) and phosphorous (P) and standardized total tract digestibility (STTD) of P in soybean expeller (SBE) and 2) to examine the effects of microbial phytase supplementation on ATTD and STTD of P in SBE. A total of 48 growing barrows (15.5 ± 0.7 kg, mean ± SD) were assigned to 1 of 8 dietary treatments (4 with 500 phytase units/kg and 4 without phytase) in a completely randomized design to give 6 replicates per treatment. SBE was the only source of P in diets. Four SBEs were used in the experiment, with three derived from soybeans grown in Manitoba (MB1, MB2, and MB3) whereas the fourth was derived from soybeans grown in Ontario. The experiment was conducted over 3 consecutive 12-day periods; within each period the initial 7 days were for adaptation followed by 5 days for total fecal collection (marker to marker procedure). Data were analyzed using the MIXED procedure of SAS. Fixed effects were the type of SBE and phytase whereas period was included as a random effect in the model. Dry matter (DM), Ca and P levels were analyzed in diets and feces. The ATTD and STTD of P were not affected by the source of SBE and averaged 63.0% and 69.9%, respectively. Phytase supplementation significantly increased (P < 0.001) P digestibility in all SBE types. The ATTD and STTD values of P with phytase supplementation averaged 72.8% and 79.7%, respectively. There was no interaction effect between type of SBE and phytase supplementation. The ATTD of Ca (P < 0.001) in MB2 was significantly lower (55.7%) than in the other SBEs whose values averaged71.6%. Ca digestibility was not affected by phytase inclusion. In conclusion, the ATTD and STTD of P were not different among the SBE types. Phytase supplementation increases the P digestibility in SBE irrespective of source.