AVAILABILITY OF PHYTATE PHOSPHORUS TO THE GROWING PIG RECEIVING ISONITROGENOUS DIETS BASED ON WHEAT OR CORN

Abstract

A factorial experiment using 48 pigs was designed to measure the availability of natural and purified phytate phosphorus to the growing (11–45 kg) pig. Factors studied included total dietary phosphorus (P) level (0.35, 0.50 or 0.65%), supplemental P source (dicalcium phosphate or calcium phytate), and cereal type (wheat or corn) used to form the base of the diets. All diets contained 0.65% calcium. Apparent P digestibility was significantly better for pigs fed supplemental P as dicalcium phosphate than as calcium phytate at dietary levels of 0.50% total P (33 vs. 19%) or 0.65% total P (43 vs. 20%). Apparent P digestibility averaged 15% with diets containing over 90% of the total P from cereals. Rate of gain and feed efficiency were impaired and bone development (metatarsal weight, percentage ash and femur breaking strength) was reduced and hypophosphataemia occurred in pigs fed diets containing the low level of P (averaging 0.35% total and 0.23% phytate P) or added calcium phytate (averaging 0.50% total and 0.38% phytate P). Responses to added P occurred to a level of 0.50% total P and up to 0.30% phytate P. This level of phytate P is the approximate upper limit normally encountered in cereal-based swine diets containing only plant proteins. It was considered that live performance and skeletal development were of equal value in assessing adequacy of dietary P supply.