高葉酸機能性雞蛋之生產

Abstract

本研究之目的，旨在評估產蛋雞飼糧強化葉酸後，其蛋中葉酸堆積的增加程度，並比較蛋雞對不同型態葉酸的吸收與利用，期以了解蛋雞對葉酸的利用情形，供往後研究的參考。 本試驗共分四部份進行，分述如下: 試驗一: 以葉酸缺乏之半純化飼糧餵飼十三週齡之新母雞，為期五週，藉以了解新母雞葉酸缺乏時，血液相及血液生化值的變化，以作為葉酸是否缺乏之指標。結果顯示，葉酸缺乏的雞隻，食慾及增重顯著降低（P＜0.05）; 血液中的紅血球數、血紅素值及紅血球比容積均顯著降低（P＜0.05），而平均血球容積則增大。血漿之葉酸含量及肝臟中儲存的葉酸量，餵飼半純化飼糧的雞隻，在耗竭期(depletion)的第四週時，已降至谷底; 而血漿高半胱胺酸之濃度則隨飼養時間的增長而顯著升高（P＜0.05），並且持續升高。綜合以上結果，血漿中的葉酸及高半胱胺酸之濃度等血液生化值，似可作為新母雞葉酸是否缺乏之指標。 試驗二: 利用新母雞四週的葉酸耗竭與四週的補滿(repletion)試驗，比較合成的氧化型喋醯麩胺酸（pteroylglutamic acid; PGA）與經消化的細菌細胞粉末(digested bacterial cell powder; DBCP, 含有天然的還原型四氫葉酸)，在新母雞體內的吸收與代謝。葉酸耗竭之雞隻，灌飼葉酸(1mg/kg BW)，一小時後其血漿葉酸濃度即迅速升高，3小時後已升高到12.5 ng/ml，幾乎達到正常水平(12-15 ng/ml)，DBCP處理組顯著（P＜0.05）高於PGA處理組。飼糧中添加不同型態葉酸，對雞隻的平均每日體增重、飼料採食量及飼料利用效率之差異則不大。葉酸添加一週之後，血漿葉酸濃度隨即迅速且顯著的升高（p＜0.05），從基準點的1.5 ng/ml升到9.2 ng/ml，第二週持續上升，到第三週時已升到12 ng/ml之正常值。DBCP處理組其血漿葉酸濃度顯著（p＜0.05）高於PGA處理組。至於血漿高半胱胺酸之濃度，餵飼缺乏葉酸的雞隻，四週之後已升高到41.8 &micro;mol/ml。而於葉酸添加一週後，隨即顯著降低（P＜0.05），並且每週持續顯著降低（P＜0.05），DBCP處理組顯著低於PGA處理組（P＜0.05）。肝中葉酸含量的情況與血漿中的情況相同。 試驗三: 60隻產蛋雞，分別飼予低葉酸之基礎飼糧或飼料中各添加5㎎/㎏PGA及DBCP之供試飼糧，為期四週。結果顯示，葉酸的添加可以提高產蛋率，其中以DBCP組最佳，顯著的優於對照組(P < 0.05 )。血漿中葉酸含量，葉酸添加組顯著高於對照組(P < 0.05 )。卵黃葉酸濃度隨著試驗期間而增加，直到第三週達到高峰後則維持穩定; 葉酸添加組顯著高於對照組(P < 0.05 )。餵食DBCP組卵黃中葉酸含量有比PGA組高的趨勢，但差異不顯著。 試驗四: 選產蛋正常之30週齡白色來航雞72隻，餵飼以玉米及大豆粕為主之基礎飼糧一週後，逢機分成兩大試驗組，飼予添加PGA或DBCP，葉酸之濃度分別為0.5、1、2、4、8及16㎎/㎏diet的12組供試飼糧，每飼糧處理組6隻，飼養試驗為期四週。隨著葉酸添加量的增加，血漿中葉酸濃度顯著提高（P＜0.05）。兩種型態之葉酸添加則無顯著差異（P > 0.05）。葉酸的添加能夠顯著降低血漿中高半胱胺酸濃度（P＜0.05），兩種型態之葉酸添加組間亦無顯著差異。卵黃中葉酸含量隨著葉酸添加量的增加而增加，在0.5㎎/㎏diet到4㎎/㎏diet之間其反應最敏銳，葉酸添加量為4㎎/㎏diet時極顯著提高卵黃中葉酸含量（P＜0.01），且已達到飽和量。從4㎎/㎏diet到16㎎/㎏diet之間，卵黃中葉酸含量雖隨著葉酸添加量的增加而增加，但差異不顯著。餵飼DBCP組卵黃中葉酸的含量則高於餵飼PGA組。 本研究發現產蛋雞確實有一相當有效的葉酸保存及遞送系統，能把吸收到血液中的葉酸轉送入卵黃中，透過增加飼糧中葉酸的添加量來提高蛋中葉酸的含量，達到生產高葉酸機能蛋的目標是可能的。卵黃中葉酸含量會隨著飼糧中葉酸添加量的增加而增加，最佳之添加量為4㎎/㎏ diet。

The role of folate in health maintenance has moved beyond the prevention of macrocytic anemia. Suboptimal folate status is now associated with neural tube defects, cardiovascular disease and certain cancers. In light of evidence supporting a need for humans to increase their dietary folate intakes, experiments were conducted to evaluate the extent to which egg folate levels could be increased, and to compare the bioavailability between reduced and oxidized forms of folate. In experiment 1, a 5 weeks folate depletion protocol was employed, using 13-week old Hyline pullets assigned to receive a semi-purified folate-deficient diet or a commercial corn-soybean meal based diet supplemented with 1 mg/kg pteroylglutamic acid (PGA). Growth performances were greatly depressed, erythrocyte, hemoglobin and hematocrit were all markedly decreased in the folate deficient birds whereas mean cell volume was increased. A 4 weeks folate depletion period was judged to be optimal on the basis of the development of nadirs in both plasma and hepatic folate stores and elevated concentrations of plasma homocysteine. In experiment 2, pullets previously maintained on a folate-devoid diet for 4 weeks, were used to compare the bioavailability of PGA with natural tetrahydrofolate (THF) from digested bacterial cell powder after a single forced feeding for 4 weeks repletion. Both forms of folate supported increases in plasma and hepatic folate stores, whereas the reduced folate lowered plasma homocysteine concentrations further than the oxidized form PGA. These data also support the use of both plasma folate and homocysteine as sensitive response criteria for folate status in pullets. In experiment 3, Hyline W-36 laying hens received a corn-based diet, containing 0, 5 mg/kg of PGA or THF, to establish the potential for folate incorporation into table eggs. Results indicated that the level of folate in the yolk reached a maximum by week 3 after folate supplementation. Fortification of dietary folate led to an increase in egg folate content of approximately 2.5 fold, from 20 &micro;g folate/egg to 50 &micro;g folate/egg and the reduced form of folate increased more. In experiment 4, 72 hens were divided into 12 treatment groups and received diets supplemented with 0.5, 1, 2, 4, 8, or16 mg folate/kg as either PGA or THF, in an attempt to establish a dose response relationship between dietary and egg folate levels. Supplementation of dietary folate increased both folate content of plasma and egg, with the most sensitive responses observed between 0.5 and 4 mg of folate/kg diet. There was no significant difference in egg folate concentrations between 4 and 16 mg folate/kg diet supplementation. Furthermore, THF treated hens increased the plasma and egg folate levels higher than the PGA. In conclusion, laying hens have highly efficient conservation and delivery systems for folates. Enrichment of eggs with folate is possible when dietary folate levels are increased. The concentration of folate in the yolk is dependent on the concentration of dietary folate and that it is saturable. Maximal egg folate levels established at approximately 4 mg folate/kg diet. THF might be preferable for the supplementation of producing high folate eggs. Increasing the folate content of eggs may position the egg as an important source of human dietary folate and lead to an improvement in consumer acceptance of this commodity as a healthful product.