Performance and phosphorus balance of pigs fed diets formulated on the basis of values for standardized total tract digestibility of phosphorus.

Three experiments were conducted to test the hypotheses that pigs fed diets that are equal in digestible P will perform equally regardless of the concentration of total P in the diets, and that the addition of microbial phytase, distillers dried grains with solubles (DDGS), or a combination of phytase and DDGS will result in a reduction in P excretion. In Exp. 1, a P-free diet and 6 diets containing corn, soybean meal (SBM), or DDGS without or with microbial phytase (500 phytase units per kg) were formulated. Diets were fed for 12 d to 42 pigs (initial BW = 13.5 +/- 3.9 kg) housed in metabolism cages that allowed for total collections of feces. Basal endogenous P losses were determined to be 199 mg/kg of DMI for pigs fed the P-free diet. Addition of phytase increased (P < 0.01) the standardized total tract digestibility (STTD) of P in corn (64.4 vs. 26.4%) and SBM (74.9 vs. 48.3%), but there was no effect (P > 0.10) of the addition of phytase on the STTD of P in DDGS (75.5 vs. 72.9%). In Exp. 2, a total of 160 pigs (initial BW = 11.25 +/- 1.95 kg; 4 pigs/pen) were allotted to 4 corn- and SBM-based diets with 2 amounts of phytase (0 or 500 phytase units per kg) and 2 amounts of DDGS (0 or 20%) in a 2 x 2 factorial arrangement of treatments. All diets were formulated to contain 0.32% STTD of P according to the STTD values determined in Exp. 1. Diets were fed for 21 d and results indicated that inclusion of phytase in the diet containing no DDGS tended (P < 0.10) to decrease G:F, but inclusion of 20% DDGS in the diets tended (P < 0.10) to increase ADG, ADFI, and final BW. In Exp. 3, the diets used in Exp. 2 were fed to 24 pigs (initial BW = 14.6 +/- 1.4 kg) that were placed in metabolism cages individually. Feces and urine were collected for 5 d. Phytase and DDGS increased (P < 0.01) the apparent total tract digestibility of P in the diets. Absorption of P was greater (P < 0.05) in pigs fed corn-SBM-DDGS diets than pigs fed corn-SBM diets, and phytase, DDGS, or the combination of phytase and DDGS reduced (P < 0.01) P excretion. In conclusion, the addition of phytase increased the STTD of P in corn and SBM, but had no effect on the STTD of P in DDGS. Diets may be formulated based on STTD values without compromising pig performance, and dietary phytase, DDGS, or the combination of phytase and DDGS will reduce P excretion by growing pigs.