EFFICACY OF PHYTASE IN IMPROVING THE BIOAVAILABILITY OF PHOSPHORUS INSOYBEAN-MEAL AND CORN-SOYBEAN MEAL DIETS FOR PIGS

Four experiments involving 225 pigs were conducted to assess the effic acy of a microbial phytase (FINASE(TM), Alko Ltd. Biotechnology, Rajam aki, Finland) produced by Aspergillus niger in corn-soybean meal or de xtrose-cornstarch-soybean meal-based diets. In two experiments with gr owing finishing pigs, fortified corn-soybean meal diets were formulate d to be adequate (.50%) or inadequate (.40 or .30%) in P during the gr owing phase followed by adequate (.40%) or inadequate (.30%) P in the finishing phase. Mono-dicalcium phosphate was the source of supplement al P. Half the diets were supplemented with phytase (500 phytase units /g). Rate and efficiency of gain and bone breaking strength were decre ased when P-deficient diets were fed. Phytase supplementation of the l ow-P diets restored growth rate and feed:gain to levels that approache d those of pigs fed the adequate-P control diet. Bone strength was par tially restored to that of the controls. In two additional experiments , pigs were fed low-P basal diets in which all the dietary P came from soybean meal or a corn-soybean meal blend. Both diets contained .05% available P. Graded levels of monosodium phosphate were added to these diets, up to .15% added P, to establish a standard curve. Phytase was added to the basal diet at 250, 500, or 1,000 units/g. Growth rate an d bone strength improved linearly (P < .01) with added monosodium phos phate and with increasing levels of supplemental phytase. Based on est imates of total and available P intakes, the highest level of phytase (1,000 units/g) increased the bioavailability of the P from 25% in the soybean meal diet to 57% in the phytase-supplemented diet, and from 1 5% in the corn-soybean diet to 43% in the phytase-supplemented diet. E xpressed on the basis of the improvement in phytate P availability, th is level of phytase converted approximately one-third of the unavailab le P to an available form. The results indicate that the phytase was e fficacious in improving the bioavailability of phytate P for pigs.