Determination of true ileal phosphorus digestibility of maize and soybean meal and true ileal calcium digestibility of soybean meal for broiler chickens

Two experiments were conducted, using the regression method, to determine the true ileal phosphorus (P) digestibility of maize and soybean meal (SBM), and true ileal calcium (Ca) digestibility of SBM for broiler chickens. The aim of Experiment 1 was to determine true ileal P digestibility of maize and SBM. The experimental diets were formulated with four inclusion levels of each test ingredient to achieve graded concentrations of total P (2.5, 3.0, 3.5 and 4.0 g/kg, respectively). The P concentrations in maize-based diets were adjusted by the inclusion of monosodium phosphate. The Ca:total P ratio in all diets was maintained at 1.35 by the addition of limestone. Experiment 2 was conducted to determine true ileal Ca digestibility of SBM. Experimental diets were formulated to contain four levels of SBM to achieve graded concentrations of Ca (2.5, 3.0, 3.5 and 4.0 g/kg, respectively). Because of the low concentration of Ca in SBM, all diets were supplemented with a similar level of limestone to prevent any Ca deficiency. The Ca:total P ratio in all diets was adjusted to be equal by the addition of monosodium phosphate. In both experiments, titanium dioxide (3 g/kg) was used as the indigestible marker. One-day-old male broiler chicks were fed a commercial starter diet from 1 to 21 days of age. On Day 22, a total of 240 and 120 birds were assigned to eight and four dietary treatments in Experiments 1 and 2, respectively, with five replicate cages and six birds per cage. Birds were fed the experimental diets for 7 days. On Day 29, ileal digesta were collected from the posterior half of ileum, and the true P and Ca digestibility of test ingredients were calculated by linear regression analysis. True P digestibility of maize and SBM were determined to be 33.8% and 42.3%, respectively. True Ca digestibility of SBM was determined to be 45.9%.