Effects of graded levels of microbial phytase on apparent total tract digestibility of calcium and phosphorus and standardized total tract digestibility of phosphorus in four sources of canola meal and in soybean meal fed to growing pigs.

One hundred twenty pigs were used to determine effects of graded levels of microbial phytase on the apparent total tract digestibility (ATTD) of P and Ca and the standardized total tract digestibility (STTD) of P in 4 sources of canola meal and in 1 source of soybean meal (SBM) fed to growing pigs. The 4 sources of canola meal were produced from 1 source of high-protein canola seeds and 2 sources of conventional canola seeds with 1 of the conventional canola seeds being divided into 2 separate batches before crushing. Pigs (16.2 ± 5.3 kg initial BW) were individually housed in metabolism crates and were randomly allotted to 1 of 20 diets in a 5 × 4 factorial arrangement of treatments with 5 ingredients and 4 levels of phytase. There were 6 replicate pigs per diet. Five basal diets based on high-protein canola meal (CM-HP), high-temperature processed canola meal (CM-HT), low-temperature processed canola meal (CM-LT), conventional canola meal (CM-CV), or SBM were formulated. The basal diets contained no phytase. Fifteen additional diets were prepared by adding approximately 500, 1,500, or 2,500 phytase units/kg to each of the 5 basal diets. Feces were quantitatively collected for 5 d based on the marker-to-marker approach after a 7-d adaptation period. Results indicated that supplementation of microbial phytase increased (linear, < 0.05) the ATTD of Ca in diets containing CM-HP, CM-HT, CM-CV, and SBM but not in diets containing CM-LT. Microbial phytase also increased (linear and quadratic, < 0.05) the ATTD and STTD of P in all 5 ingredients. Compared with the CM-CV diets, the CM-HP diets had greater ( < 0.05) ATTD of Ca. The ATTD of Ca in the SBM diet was greater ( < 0.05) than in all canola meal diets, but no differences were observed in ATTD of Ca between CM-HT and CM-LT diets. The ATTD and the STTD of P were less ( < 0.05) in CM-HP, CM-HT, CM-LT, or CM-CV than in SBM if no microbial phytase was added, but no differences were observed in the ATTD and STTD of P in SBM, CM-HP, CM-HT, or CM-CV if the highest amount of phytase were added (interaction, < 0.05). Regression equations were developed to calculate the response to microbial phytase on the STTD of P in CM-HP, CM-HT, CM-LT, CM-CV, and SBM. In conclusion, inclusion of graded levels of microbial phytase increased the ATTD and STTD of P in CM-HP, CM-HT, CM-LT, CM-CV, and SBM and the response to microbial phytase added to each ingredient can be predicted by regression equations.