Effects of Extrusion and Microbial Phytase on the Apparent and Standardized Total Tract Digestibility of Phosphorus in Hemp Hulls Fed to Growing Pigs

The objective of this study was to determine the apparent total tract digestibility (ATTD) and the standardized total tract digestibility (STTD) of P and the effects of extrusion and microbial phytase on ATTD and STTD of P in hemp hulls (HH). Thirty-six pigs (30.3 ± 2.7 kg) were assigned to 1 of 6 experimental diets in a complete randomized design to give 6 replicates per diet. A corn-soybean meal (SBM)-based basal diet was formulated. Two additional diets were formulated by replacing 40% of corn and SBM with HH or extruded HH (EHH). The test ingredients, corn, and SBM were the only sources of P in the diets. Three additional diets were also formulated by supplementing 500 phytase unit/kg of microbial phytase to the initial 3 diets (a corn-SBM basal diet and diets containing test ingredients). Pigs were fed experimental diets at 3 times the maintenance energy requirement (197 kcal ME/kg BW^0.60). Results indicated that fecal P concentration and daily P output were reduced (P < 0.05) from pigs fed diets with dietary phytase compared to pigs fed diets without dietary phytase. The ATTD and STTD of P in experimental diets were not different and averaged 39.6% and 43.7%, respectively. However, the ATTD and STTD of P in experimental diets supplemented with dietary phytase were increased (P < 0.05) compared to the diets without phytase. The ATTD and STTD of P in HH were 18.8% and 22.0%, respectively, whereas, respective values for EHH were 22.5% and 26.3%. Extrusion had no effects on ATTD and STTD of P in HH. However, the ATTD and STTD of P in HH and EHH increased (P < 0.05) when dietary phytase was added to the diets. In conclusion, the ATTD and STTD of P in HH fed to growing pigs were 18.8% and 22.0%, respectively. Respective values for EHH were 22.5% and 26.3%. Extrusion process did not affect the ATTD and STTD of P in HH. However, the addition of microbial phytase to experimental diets increased the ATTD and STTD of P in diets and test ingredients and decreased fecal P output from pigs fed experimental diets. There was no interaction between extrusion and dietary phytase supplementation.