Increasing levels of microbial phytase increases the digestibility of energy and minerals in diets fed to pigs

The objective of this experiment was to test the hypothesis that increased dietary concentrations of a novel E. coli phytase (Smizyme) improve the apparent total tract digestibility (ATTD) of energy, dry matter (DM), calcium (Ca), phosphorus (P), and micro minerals in corn-soybean meal based diets fed to growing pigs. A total of 56 growing pigs (initial body weight: 13.6 ± 1.15 kg) were allotted to a randomized complete block design with 7 diets. Pigs were divided into 2 blocks with 28 pigs and 4 replicate pigs per diet in each block, for a total of 8 replicate pigs per diet. A positive control without phytase was formulated to contain 0.70% Ca and 0.33% standardized total tract digestible (STTD) P. A negative control diet that was similar to the positive control diet with the exception that the concentration of Ca and STTD P were reduced to 0.50 and 0.16%, respectively, was formulated by removing the dicalcium phosphate and increasing the concentration of limestone. Five additional diets that were similar to the negative control diet, but contained 250, 500, 1000, 1500, or 2500 units of microbial phytase per kg were also used. The ATTD of gross energy (GE), dry matter (DM), nitrogen (N), Ca, P, sodium (Na), potassium (K), magnesium (Mg), sulfur (S), zinc (Zn), copper (Cu), iron (Fe), and manganese (Mn) in each diet were calculated. Data were analyzed using contrast statements. Data for ATTD and retention of P and Ca, were also analyzed using a single broken-line model. Results indicated that N retention and concentration of digestible energy (DE) and metabolizable energy (ME) of diets increased (linear, P < 0.05) as the concentration of phytase increased in the diets. The ATTD of Ca and P, and the STTD of P increased (linear and quadratic, P < 0.05) as phytase concentration increased in the diets. The concentration of phytase required for maximum retention of P and Ca was greater (P < 0.05) than the concentration required for maximum ATTD of P and Ca. The ATTD of K, Na, Mg, and Zn increased (linear, P < 0.05) as phytase increased in the diets, but that was not the case for S, Cu, Fe, and Mn. In conclusion, ATTD of GE, DM, and most macro and micro minerals increased if increased levels of phytase were added to corn-soybean meal diets that contained no inorganic P. Fecal excretion of Ca and P was reduced, and retention of Ca and P was increased by adding phytase to the diets, whereas most parameters for N balance were not affected by addition of phytase to the diets.