Efficacy of a recombinant-derived phytase in improving the bioavailability of phosphorus in corn-soybean meal diets for pigs

Three experiments involving 162 pigs were conducted to assess the efficacy of phytase (Natuphos[TM]; BASF, Mount Olive, NJ) in low-P, corn-soybean meal-based diets. The phytase was produced by a recombinant Aspergillus niger. The phytase supplement contained 5,000 phytase units (PTU)/g. In Exp. 1 (66 pigs) and 2 (60 pigs), growing-finishing pigs were fed fortified corn-soybean meal diets formulated to be adequate (.50%), marginal (.425%), or inadequate (.35%) in P during the growing phase (23 to 60 kg BW) followed by adequate (.40%), marginal (.35%), or inadequate (.30%) P, respectively, during the finishing phase (to 104 kg BW). Dicalcium phosphate was the source of supplemental P. In addition, the low-P sequence (.35/.30% P) was supplemented with phytase at 250, 500, or 1,000 PTU/kg. Rate and efficiency of gain decreased linearly (P < .01) and bone breaking strength decreased quadratically (P < .01) as the concentration of P was decreased in the diets. Responses in growth and bone traits to increasing levels of phytase activity in the low-P diet were linear (P < .01). The highest level of phytase in the low-P diet restored growth rate and bone breaking strength to levels that approached or met those of pigs fed the adequate P diet. In Exp. 3, 36 growing pigs (15 kg BW) were fed a low-P (.32% total P; .05% available P) basal diet supplemented with graded levels of monosodium phosphate (MSP) to provide 0, .075, and .15% added P or with phytase to supply 240, 420, or 830 PTU/kg for 36 d. Performance and bone strength increased linearly with increasing levels of MSP and with increasing levels of supplemental phytase (P < .01). However, the highest level of phytase (830 PTU/kg) did not bring performance or bone mineralization up to that achieved by pigs fed the highest level of inorganic P. Based on bone strength and total and available P intakes, the three levels of phytase increased the bioavailability of the P from 15% in the corn-soybean meal mixture to 20, 27, and 39% in the diets containing 240, 420, and 830 PTU/kg, respectively. Approximately 29% of the unavailable P was made available by the highest level of phytase addition. Phytase improved the absorption of P from corn and soybean meal and decreased the amount of P excreted. These results indicate that the phytase was effective in improving the bioavailability of phytate P for pigs. Based on a comparison of the linear responses to inorganic P and to phytase supplementation, the data indicated that for every 100 phytase units included per kilogram of diet, the level of inorganic P can be reduced by .0085 percentage units. Key Words: Pigs, Phytase, Phosphorus, Availability