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تعداد صفحات این فایل: ۱۸ صفحه

بخشی از مقاله انگلیسیعنوان انگلیسی:The Effects of Supplemental Microbial Phytase on the Performance and Utilization of Dietary Calcium, Phosphorus, Copper, and Zinc in Broiler Chickens Fed Corn-Soybean Diets~~en~~

Abstract

A 3-wk feeding trial with 180 sexed day-old broiler chickens was conducted to study the efficacy of microbial phytase (Natuphos 1000) on growth performance, relative retention of P, Ca, Cu, and Zn, and mineral contents of plasma and bone. Treatments involved a normal P level corn-soybean diet, a low-P diet, and a low-P plus phytase (600 phytase units/kg) diet. Phytase supplementation increased (P 005) body weight in male and female chickens by 13.2 and 5.8%, respectively, at 21 d. The improvements yielded body weights comparable to those obtained on the normal P diet. Phytase supplementation overcame (P 005) the depression of feed intake observed on the low-P diet. Treatments had no effect on feed:gain ratio. Phytase supplementation of the low-P diet increased (P 005) the relative retention of total P, Ca, Cu, and Zn by 12.5, 12.2, 19.3, and 62.3 percentage units, respectively, in male chickens. Microbial phytase increased the plasma P by 15.7% and reduced (P 005) the Ca concentration by 34.1%, but had no effect on plasma concentrations of Cu or Zn. Phytase supplementation increased the percentage ash in both head and shaft portions of dry, fat-free tibia bone to a level comparable to that of the normal-P diet. Phytase supplementation had no effect on the concentration of any of the minerals measured in whole tibia ash but did increase (P 005) the DM percentage of P and Ca in tibia head of male chickens by 0.65 and 1.4 percentage units, respectively. These results show that microbial phytase supplementation of a low-P diet increased growth and relative retention of total P, Ca, Cu, and Zn and improved bone mineralization in broiler chickens.

۱ Introduction

Plant materials are the major constituents of poultry diets. About two-thirds of the P of plant origin is present as phytic acid in the form of myo-inositol phosphates (Cromwell, 1980). Phosphorus in the phytic acid form is poorly available to monogastric animals because they lack phytase, the enzyme that hydrolyzes phytic acid into inositol and orthophosphate (Peeler, 1972). It is well documented that microbial phytase supplementation improves the availability of phytate-bound P in broiler chickens (Nelson et al., 1971; Simons et ah, 1990; Roberson and Edwards, 1994). However, there is little information about the availability of trace minerals when the broiler diet is supplemented with microbial phytase.

Phytate, being a strong acid can form various salts with the important minerals such as Ca, Mg, Cu, Zn, Fe, and K, thus reducing their solubility (Eardman, 1979). Nutritionally more important is the fact that maximum binding of Zn-Ca-Cu-phytate as well as Cu-Ca-phytate occurs at pH 6, which is the normal pH of the duodenum, where maximum absorption of divalent cations takes place (Oberleas, 1973). When phytic acid is hydrolyzed by microbial phytase it may release all phytate-bound minerals. However, in a very recent study, Aoyagi and Baker (1995) have shown that microbial phytase supplementation reduced the Cu utilization by 50% in chickens fed soybean meal. The authors speculated that phytase may have increased the Zn bioavailability in soybean meal and the released Zn might have had antagonized the absorption of Cu. In another study with broiler chickens, Roberson and Edwards (1994) have shown that phytase addition to a corn-soybean meal diet did not affect the Zn retention whereas phytase plus 1,25-dihydroxycholecalciferol [l,25-(OH)2D3] increased Zn retention. The lack of information and contradictions concerning the efficacy of phytase on the availability of trace minerals indicate the need for more investigation. Therefore, the objectives of this study were to determine the effects of microbial phytase supplementation on the performance of broiler chickens fed low-P corn-soybean meal diets,and to study the efficacy of microbial phytase on the apparent availability of Ca, P, and trace minerals such as Cu and Zn and on the mineral contents of bone and plasma.

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