Effects of level of supplemental phytase on ileal digestibility of amino acids, calcium, and phosphorus in dehulled soybean meal for growing pigs

Ileally cannulated pigs were used to assess the effects of four dietary lev els of microbial phytase (Natuphos) on the apparent and true digestibility of Ca, P, CP, and AA in dehulled soybean meal. Fourteen pigs (25 kg initial BW) were surgically fitted with T-cannulas at the terminal ileum and assig ned to diets in a replicated 7 x 7 Latin square design. Following a 14-d re covery, four diets consisting of 30.5% soybean meal with 0, 500, 1,000, or 1,500 units of phytase/kg of diet were fed. Diets 5 (1.05% lysine, 0.90% Ca , and 0.75% P) and 6 (1.05% lysine, 0.90% Ca, and 0.75% P) contained 35.25% soybean meal and 27.0% soy protein concentrate, respectively. Diet 7 (0.37 % lysine, 0.03% Ca, and 0.05% P) was a low-CP, casein-based diet used to es timate the nonspecific endogenous losses of Ca, P, CP, and AA in order to e stimate the true digestibility of these nutrients. All diets contained corn starch and dextrose and were fortified with vitamins and minerals. Chromic oxide was used as an indigestible indicator. The diets were fed daily at 9% of metabolic BW (BW0.75). Apparent and true ileal digestibility of P incre ased quadratically (P < 0.01) and true digestibility of Ca increased linear ly (P < 0.07) with increasing levels of phytase. Apparent digestibility of Ca was unaffected (P = 0.15) by phytase level. Apparent and true ileal dige stibility of CP and most AA increased slightly with the addition of 500 uni ts of phytase/kg of diet, but not at higher levels of phytase supplementati on (in most cases, cubic effect, P < 0.05). Apparent and true ileal nutrien t digestibility coefficients were unaffected by soybean meal source (Diet 1 vs Diet 5), except for arginine and Ca. The apparent and true digestibilit y coefficients for most of the AA tended (P < 0.10) to be lower in diets co ntaining soy protein concentrate vs the common source of soybean meal used in Diet 5, but ileal digestibilities of Ca and P were unaffected (P = 0.15) . In this study, supplemental microbial phytase did not improve the utiliza tion of AA provided by soybean meal but was an effective means of improving Ca and P utilization by growing swine fed soybean meal-based diets.