Soaking increases the efficacy of supplemental microbial phytase in a low-phosphorus corn-soybean meal diet for growing pigs.

Sixty-three crossbred barrows averaging 18.7 kg initial BW were used in a 6-wk study of the effects of soaking on the efficacy of supplemental microbial phytase (Natuphos, BASF) in a low-P corn-soybean meal diet. The basal corn-soybean meal diet contained .06% available P, .32% total P, and .55% Ca with no added inorganic P. The basal diet was supplemented with 0, 250, or 500 phytase units (PU)/kg of diet. The diet was fed dry or soaked (2 parts water:1 part diet and mixed for 2 h at 30 degrees C before feeding) in a 3 x 2 factorial arrangement. A positive control diet was supplemented with inorganic P and provided .23% available P, .48% total P, and .60% Ca. Pigs were individually penned and fed their respective diets to appetite in four equal meals daily. There were no soaking x phytase interactions (P > .1 to .6) for growth performance criteria. Daily gain and gain/feed ratio were increased (P < .01) by soaking and increased linearly (P < .01) by phytase. Daily feed intake was increased linearly (P < .01) by phytase. There were soaking x phytase quadratic interactions (P < .01) for apparent P absorption criteria because soaking the 250 PU/kg diet increased P absorption similar to that obtained with the 500 PU/kg diet fed dry. Apparent P absorption criteria were increased by soaking (P < .01) and were increased linearly (P < .001) and quadratically (P < .03) by phytase. Phytase reduced fecal P excretion 37 to 40% with dry feeding (P < .03) and 48 to 49% with soaking (P < .01).