EFFICACY OF LOW-ACTIVITY, MICROBIAL PHYTASE IN IMPROVING THE BIOAVAILABILITY OF PHOSPHORUS IN CORN-SOYBEAN MEAL DIETS FOR PIGS

Two experiments involving 115 pigs were conducted to assess the effica cy of a microbial phytase (Allzyme Phytase(TM); Alltech, Nicholasville , KY) produced by Aspergillus niger in low-P, corn-soybean meal-based diets. The phytase supplement contained 50 phytase units/g and 1.43% P . In Exp. 1, growing-finishing pigs were fed fortified corn-soybean me al diets formulated to be adequate (.50%) or inadequate (.30%) in P du ring the growing phase (38 to 57 kg BW) followed by adequate (.40%) or inadequate (.30%) P, respectively, during the finishing phase (to 101 kg BW). Dicalcium phosphate was the source of supplemental P. Half th e diets were supplemented with phytase at 500 phytase units/kg. Rate a nd efficiency of gain and bone breaking strength were decreased (P < . 01) when the low-P diet was fed. Adding phytase to the low-P diet rest ored performance and bone breaking strength (P < .01) to levels that a pproached those of pigs fed the adequate-P diet. In Exp. 2, growing pi gs (13 kg BW), were fed a low-P (.32% total P; .048% available P) basa l diet supplemented with graded levels of monosodium phosphate to prov ide 0, .075, and .15% added P or with phytase to supply 250, 500, 1,00 0, or 2,000 phytase units/kg. Chromic oxide was included as an indiges tible marker for determining apparent absorption and fecal excretion o f P. Performance and bone strength increased linearly with added monos odium phosphate (P < .01) and with increasing levels of supplemental p hytase (P < .05). A portion of these increases from phytase was attrib uted to the P supplied by the phytase mix (.007, .014, .028, .057%, re spectively). Based on bone strength and total and available P intakes, the four levels of phytase increased the bioavailability of the P in the corn-soybean meal mixture by 4, 5, 8, and 15 percentage units, res pectively. Approximately 4, 7, 10, and 15% of the unavailable P was ma de available by the four levels of phytase, respectively. Phytase incr eased (P < .01) the apparent absorption of the corn-soybean meal P. Ph ytase did not affect the daily excretion of P, but it reduced (P < .01 ) the percentage of dietary P that was excreted in the feces. These re sults indicate that this source of phytase was moderately efficacious in improving the bioavailability of phytate P for pigs.