Efficacy of a genetically modified yeast phytase on phosphorus bioavailability in a corn-soybean meal based diet for growing pigs

We investigated the efficacy of genetically modified yeast (GMY) phytase on phosphorus (P) bioavailability in growing pigs fed a corn–soybean meal based diet. Crossbred barrows were fed a P-adequate, a low-P or a P-deficient diet containing 0.37, 0.27 and 0.14% non-phytate-P, respectively. The P-deficient diet was supplemented with wild-type yeast (WTY), Aspergillus (ASP) or GMY phytase at 750 PU per kilogram of food. Dietary ASP and GMY phytases increased plasma inorganic P (P_i) concentration and the apparent absorption of P, and decreased the concentration of a bone resorption marker, plasma type-I collagen C-terminal telopeptide (ICTP). Wild-type yeast phytase also increased the apparent absorption of P, but the changes in plasma P_i and ICTP concentrations were not significant. Although the dietary P_i-equivalencies based on plasma P_i and ICTP concentrations did not differ between WTY and ASP phytases, the equivalency of ASP phytase based on apparent absorption of P was higher than that of WTY phytase. The equivalency of GMY phytase calculated from each parameter was higher than that of WTY phytase, and did not differ from that of ASP phytase. These results suggest that efficacy of GMY phytase on P bioavailability was higher than WTY phytase, and as effective as ASP phytase in growing pigs.