Efficacy of an E. coli phytase expressed in yeast for releasing phytate-bound phosphorus in young chicks and pigs.

Four chick trials and one pig trial were conducted to investigate the phosphorus-releasing efficacy oftwo commercial phytase enzymes (Natuphos and Ronozyme) and an experimental E. coli phytase enzyme (ECP) when added to corn-soybean meal diets containing no supplemental inorganic P (iP). In the 13- or 14-d chick trials, three or four graded levels of iP (0, 0.05,0.10,0.15%) from KH2PO4 were added to the basal diet to construct standard curves from which bioavailable P release could be calculated for the phytase treatments. In all cases, phytase supplementation levels were based on an assessment of phytase premix activity (i.e., P release from Na phytate at pH 5.5). Linear (P < 0.01) responses in tibia ash and weight gain resulted from iP supplementation in all assays. In the first chick trial, supplementation of 500 phytase units (FTU)/kg of ECP resulted in superior (P < 0.01) weight gain and tibia ash values compared with 500 FTU/kg of Natuphos. Results of the second chick trial revealed P-release values of 0.032 and 0.028% for 500 FTU/kg Natuphos and Ronozyme, respectively, and these were lower (P < 0.01) than the 0.125% P-release value for 500 FTU/kg of ECP. Tibia ash responded quadratically (P < 0.05) in response to graded levels of ECP up to 1,500 FTU/kg in the third chick trial. Combining Natuphos with either Ronozyme or ECP in Chick Trial 4 revealed no synergism between phytases with different initiation sites of P removal. The pig trial involved 10 individually fed weanling pigs per diet, and and phytase enzymes were supplemented to provide 400 FTU/kg in diets containing 0.60% Ca. Based on the linear regression of fibula ash on supplemental iP intake (r2 = 0.87), P-release values were 0.081% for Natuphos, 0.043% for Ronozyme, and 0.108% for ECP. These trials revealed an advantage of the E. coli phytase over the commercial phytases in young chicks.