Measurement of true ileal digestibility of phosphorus in some feed ingredients for broiler chickens.

An experiment was conducted to estimate the true ileal digestibility of P in wheat, sorghum, soybean meal, and corn distiller's dried grains with solubles (DDGS) in broiler chickens. Four semipurified diets were formulated from each ingredient (wheat and sorghum: 236.5, 473, 709.5, and 946 g/kg; soybean meal and corn DDGS: 135, 270, 405, and 540 g/kg) to contain graded concentrations of nonphytate P. The experiment was conducted as a randomized complete block design with 4 weight blocks of 16 cages each (5 birds per cage). A total of 320 21-d-old broilers (Ross 308) were assigned to the 16 test diets with 4 replicates per diet. Apparent ileal digestibility coefficients of P were determined by the indicator method and the linear regression method was used to determine the true P digestibility coefficients. The results showed that the apparent ileal P digestibility coefficients of wheat-based diets were not influenced (P>0.05) by increasing dietary P concentrations, whereas those of diets based on sorghum, soybean meal, and corn DDGS differed (P<0.05) at different P concentrations. Apparent ileal P digestibility in broilers fed diets with soybean meal and corn DDGS linearly (P<0.001) increased with increasing P concentrations. True ileal P digestibility coefficients of wheat, sorghum, soybean meal, and corn DDGS were determined to be 0.464, 0.331, 0.798, and 0.727, respectively. Ileal endogenous P losses in birds fed diets with wheat, soybean meal, and corn DDGS were estimated to be 0.080, 0.609, and 0.418 g/kg DMI, respectively. In birds fed sorghum-based diets, endogenous P losses were estimated to be negative (-0.087 g/kg DMI). True digestible P contents of wheat, sorghum, soybean meal, and corn DDGS were determined to be 1.49, 0.78, 5.16, and 5.94 g/kg, respectively. The corresponding nonphytate P contents in wheat, sorghum, soybean meal, and corn DDGS were 1.11, 0.55, 2.15, and 4.36 g/kg, respectively. These differences between digestible P and nonphytate P contents may be suggestive, at least in part, of overestimation of P digestibility under the calcium-deficient conditions used in the regression method.