ADDING WHEAT MIDDLINGS, MICROBIAL PHYTASE, AND CITRIC-ACID TO CORN-SOYBEAN MEAL DIETS FOR GROWING PIGS MAY REPLACE INORGANIC PHOSPHORUS SUPPLEMENTATION

Three experiments were conducted with 96 growing Landrace x Yorkshire x puree crossbreds to determine the collective effectiveness of cereal phytase from wheat middlings, microbial phytase, and citric acid in i mproving phytate-P bioavailability in corn-soy diets. In Exp. 1, 40 gi lts (7 wk old) were fed five diets for 8 wk. Diets 1, 2, and 3 were lo w-P, corn-soybean meal diets (CSB) + 0, .1, or .2% inorganic P (P-i) a s calcium phosphate, respectively. Diet 4 was a similar corn-soy diet that included 15% wheat middlings (461 cereal phytase U/kg). Diet 5 wa s the CSB + microbial phytase (1,200 U/kg; Natuphos, BASF, Mount Olive , NJ). In Exp. 2, 16 barrows (8 wk old) were fed two diets for 6 wk. D iet 1 was the same as Diet 3 of Exp. 1 (.2% P-i). Diet 2 was Diet 4 of Exp. 1 + microbial phytase (300 U/kg). In Exp. 3, 40 barrows and gilt s (6 wk old) were fed four diets for 6 wk. Diets 1 and 2 were the same as those in Exp. 2. Diet 3 was Diet 2 of Exp. 2 + 1.5% citric acid. D iet 4 was similar to Diet 3 but contained 10 instead of 15% wheat midd lings. In Exp. 1, pigs fed the low-P, CSB (Diet 1) had lower(P < .05) ADG, ADFI, plasma P-i concentration, bone strength, and mobility score than pigs of the other four treatments. Measurements for pigs fed the 15% wheat middlings diet were not significantly different from those of pigs fed the CSB + .1% P-i or microbial phytase. In Exp. 2, ADG(P = .06) during wk 1 to 3 and gain:feed ratio (P < .02) and plasma P-i co ncentration (P < .005) during all weeks favored pigs fed the CSB + .2% P-i compared with the other diet including 15% wheat middlings. In Ex p. 3, identical ADG during all weeks and similar plasma P-i concentrat ions at wk 4 and 6 were observed between pigs fed the two citric acid diets (Diets 3 and 4) and the CSB + .2% P-i (Diet 1). Pigs fed Diet 4 (10% wheat middlings) had even higher (P < .02) gain:feed ratio during wk 1 to 3 than those fed Diet 1. It seems feasible to completely repl ace calcium phosphate with 10 to 15% wheat middlings, 300 U microbial phytase/kg, and 1.5% citric acid in the corn-soy diets for growing pig s.