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 fo ur 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-s oyabean meal-casein (casein control diet) were tested. The maize starch con trol diet was used to evaluate the ability of chicks to utilize phytate P w hen 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 tha t the diet contained greater amounts of available P and less phytate P. Exp eriment 2 was conducted on a 3 x 2 factorial arrangement, consisting of thr ee 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 sig nificantly (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 phytat e P was utilized by the chicks fed on the maize starch control diet. Substi tuting part of the maize and soyabean meal with casein did not affect the t otal 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 phyta te P. The coarser the GMD (894 vs 573 and 484 mu m), the greater the utiliz ation of these nutrients. There were no two-way interaction effects of part icle sizes and phytase. (C) 2000 Elsevier Science B.V. All rights reserved.