Effect of phytate, microbial phytase, fiber, and soybean oil on calculated values for apparent and standardized total tract digestibility of calcium and apparent total tract digestibility of phosphorus in fish meal fed to growing pigs

Two experiments were conducted to determine the effects of phytate, phytase, fiber, and soybean oil on apparent total tract digestibility (ATTD) and standardized total tract digestibility (STTD) of Ca and on ATTD of P in fish meal fed to growing pigs. In Exp. 1, 40 growing pigs (initial average BW: 19.16 ± 2.04 kg) were randomly allotted to 1 of 5 diets with 8 pigs per treatment and placed in metabolism crates. Four diets were used in a 2 × 2 factorial design with 2 levels of phytate (0 or 0.7%) and 2 levels of microbial phytase (0 or 500 phytase units/kg). The diet containing no phytate was based on sucrose, cornstarch, fish meal, casein, and soybean oil, and the diet containing 0.7% phytate was based on corn, corn germ, fish meal, casein, and soybean oil. A Ca-free diet was used to determine basal endogenous losses of Ca. Feces were collected from d 6 to 13 after a 5-d adaptation period. Results indicated that the ATTD and STTD of Ca in fish meal and the ATTD of P increased (P < 0.001) if phytase was used and were greater (P < 0.05) in the diets based on corn and corn germ. Experiment 2 was conducted to determine the effects of fiber and soybean oil on the ATTD and STTD of Ca and the ATTD of P in fish meal. Fifty growing pigs (initial average BW: 19.36 ± 0.99 kg) were randomly allotted to 1 of 5 diets with 10 pigs per treatment. Two diets contained sucrose, cornstarch, fish meal, casein, and either 0 or 8% of a synthetic source of fiber. Two additional diets contained fish meal, casein, corn, and either 1 or 7% soybean oil. A Ca-free diet was also used. Pigs were housed individually in metabolism crates and fecal samples were collected. Results indicated that fiber increased (P < 0.001) the ATTD and STTD of Ca and the ATTD of P, but the ATTD and STTD of Ca or the ATTD of P were not affected by soybean oil. In agreement with the results of Exp. 1, the ATTD and STTD of Ca and the ATTD of P in the corn-based diet were greater (P < 0.05) than in the cornstarch-based diet. In conclusion, phytase and fiber increased the ATTD and STTD of Ca and the ATTD of P in fish meal, but inclusion of soybean oil did not affect digestibility of Ca or P. The observation that values for the ATTD and STTD of Ca and ATTD of P are greater in corn-based diets than in cornstarch-based diets indicates that values for the digestibility of Ca and P obtained in cornstarch-based diets may not always be representative for the digestibility in practical corn-based diets.