Effect of sources of maize and maize particle sizes on the utilization of phytate phosphorus in broiler chicks

Two experiments were conducted to test the effects of sources of maize and maize particle sizes on the utilization of phytate P in broiler chicks fed on maize-soyabean meal diets deficient in P. In Experiment 1, maize from four consignments was ground separately using the same milling facility. Four maize-soyabean diets representing each maize source, and two control diets made of maize-starch-soyabean meal (maize starch control diet) and maize-soyabean meal-casein (casein control diet) were tested. The maize starch control diet was used to evaluate the ability of chicks to utilize phytate P when they were provided solely by soyabean meal. The casein control diet had similar amounts of total P as the diets containing the four maize sources, but part of the maize and soyabean meal was substituted with casein so that the diet contained greater amounts of available P and less phytate P. Experiment 2 was conducted on a 3 x 2 factorial arrangement, consisting of three diets each containing maize differing in geometric mean diameter (GMD), and two levels of dietary phytase at 0 and 600 FTU/kg. Sources of maize significantly (p<0.05) influenced Ca, total P, and phytate P utilization, and the amount of ME derived from the diets. Only 0.248 of soyabean meal phytate P was utilized by the chicks fed on the maize starch control diet. Substituting part of the maize and soyabean meal with casein did not affect the total P utilization but reduced Ca utilization, possibly due to the binding of Ca in the gut with phytate P not utilized by the chicks. Maize particle sizes significantly (p<0.05) affected utilization of Ca, total P, and phytate P. The coarser the GMD (894 vs 573 and 484 mu m), the greater the utilization of these nutrients. There were no two-way interaction effects of particle sizes and phytase. (C) 2000 Elsevier Science B.V. All rights reserved.