SOAKING INCREASES THE EFFICACY OF SUPPLEMENTAL MICROBIAL PHYTASE IN ALOW-PHOSPHORUS CORN-SOYBEAN MEAL DIET FOR GROWING PIGS

Sixty-three crossbred barrows averaging 18.7 kg initial BW were used i n a 6-wk study of the effects of soaking on the efficacy of supplement al microbial phytase (Natuphos(R), 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 s upplemented with 0, 250, or 500 phytase units (PU)/kg of diet. The die t 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 po sitive control diet was supplemented with inorganic P and provided .23 % available P, .48% total P, and .60% Ca. Pigs were individually penne d and fed their respective diets to appetite in four equal meals daily . There were no soaking x phytase interactions (P > .1 to .6) for grow th performance criteria. Daily gain and gain/feed ratio were increased (P < .01) by soaking and increased linearly (P < .01) by phytase. Dai ly feed intake was increased linearly (P < .01) by phytase. There were soaking x phytase quadratic interactions (P < .01) for apparent P abs orption criteria because soaking the 250 PU/kg diet increased P absorp tion similar to that obtained with the 500 PU/kg diet fed dry. Apparen t P absorption criteria were increased by soaking (P < .01) and were i ncreased linearly (P < .001) and quadratically (P < .03) by phytase. P hytase reduced fecal P excretion 37 to 40% with dry feeding(P < .03) a nd 48 to 49% with soaking (P < .01).