以白肉雞為動物模式評估大豆粕、大豆油或不同產地玉米之可代謝能濃度

Abstract

玉米為白肉雞（broiler chicken）以玉米和大豆粕為大宗原料組成之飼糧中主要能量來源，其表面可代謝能（apparent metabolizable energy, AME）是否準確，會影響飼糧配方、飼料轉換率（feed conversion ratio, FCR）與生產成本。傳統原料 AME 資料多來自成熟蛋公雞、固定日齡白肉雞或特定飼糧條件下；然而，快速生長之白肉雞於育雛期、生長期與肥育期之消化道發育、採食量（feed intake）及營養分利用能力不同，因此同一原料在不同生長階段所呈現之可利用能量可能不完全相同。因此，本研究以白肉雞為動物模式，評估大豆粕、大豆油或不同產地玉米於不同生長階段之 AME，並檢視主要原料 AME 測定方法之適用性。 本研究分為二個試驗。試驗一以 0 日齡 Ross 308 白肉雞進行 35 日試驗，設置 0、10、20 及 30% 葡萄糖處理組，並以葡萄糖等比例取代纖維素，使葡萄糖與纖維素總添加比例固定為 30%，藉由迴歸法估算葡萄糖之 AME。結果顯示，白肉雞生長表現、採食量、FCR 及乾物質消化率皆隨飼糧中葡萄糖濃度提高而改善。然而，迴歸法估算所得各階段葡萄糖 AME 皆高於葡萄糖總能 3697.81 kcal/kg，顯示高比例纖維素並非完全惰性填充物，會影響乾物質消化率及迴歸估算之生理合理性。因此，試驗一結果指出，以高比例纖維素搭配葡萄糖進行迴歸估算，並不適合作為後續玉米 AME 測定模式。 試驗二改採替代法，以 0 日齡 Ross 308 白肉雞進行 35 日試驗，處理組包括基礎飼糧組、90% 基礎飼糧搭配 10% 美國玉米、阿根廷玉米或國產玉米組，以及 95% 基礎飼糧搭配 5% 大豆粕或大豆油組。各原料 AME 結果顯示，美國玉米於 0-10、10-21、21-35 及 0-35 日齡分別為 4636.18、4787.30、3402.49 及 3977.23 kcal/kg，階段間呈接近顯著之趨勢（P = 0.05）；阿根廷玉米分別為 3972.72、4576.82、3748.52 及 3672.23 kcal/kg，階段間未達顯著差異（P > 0.05）；國產玉米分別為 5066.33、5015.84、3521.38 及 3925.40 kcal/kg，階段間達顯著差異（P < 0.05）；大豆粕分別為 2636.41、4237.58、2190.01 及 2010.96 kcal/kg，階段間達顯著差異（P < 0.01）；大豆油分別為 6874.27、7544.62、8726.15 及 7281.17 kcal/kg，階段間未達顯著差異（P > 0.05）。 綜合而言，試驗一顯示高比例纖維素迴歸模式不適合估算葡萄糖 AME；試驗二顯示不同原料於白肉雞不同生長階段之 AME 變化模式並不一致。以替代法建立原料 AME 資料時，應同時參考乾物質消化率、能量消化率及飼糧 AME 差異，以提高原料之 AME 應用於白肉雞分階段飼糧配方時之合理性。

Corn is the major energy source in broiler diets composed mainly of corn and soybean meal. The accuracy of its apparent metabolizable energy (AME) affects diet formulation, feed conversion ratio (FCR), and production cost. However, conventional metabolizable energy data are often obtained from adult roosters, broilers at a fixed age, or specific dietary conditions, and may not fully reflect energy utilization in fast-growing broilers at different growth stages. Therefore, this study evaluated the apparent metabolizable energy concentration of soybean meal, soybean oil, or corn from different origins in broilers at different growth stages and examined the applicability of methods for determining the metabolizable energy concentration of major feed ingredients. This study consisted of two experiments. In Experiment 1, 0-day-old Ross 308 broilers were used in a 35-day trial. Four dietary treatments were prepared with 0, 10, 20, and 30% glucose, in which glucose replaced cellulose proportionally while the total inclusion level of glucose and cellulose was fixed at 30%. The regression method was used to estimate the apparent metabolizable energy concentration of glucose. Growth performance, feed intake, feed conversion ratio, and dry matter digestibility improved as dietary glucose concentration increased. However, the estimated apparent metabolizable energy concentration of glucose at all growth stages was higher than the gross energy of glucose, 3697.81 kcal/kg, indicating that a high proportion of cellulose was not a completely inert filler and affected dry matter digestibility as well as the physiological validity of the regression estimation. Therefore, the regression model using a high proportion of cellulose with glucose was not suitable for subsequent determination of corn metabolizable energy concentration. In Experiment 2, the substitution method was used in a 35-day trial with 0-day-old Ross 308 broilers. Treatments included a basal diet, diets containing 90% basal diet with 10% United States corn, Argentina corn, or domestic corn, and diets containing 95% basal diet with 5% soybean meal or soybean oil. The apparent metabolizable energy concentrations of United States corn at 0-10, 10-21, 21-35, and 0-35 days of age were 4636.18, 4787.30, 3402.49, and 3977.23 kcal/kg, respectively, showing a tendency to differ among stages (P = 0.05). The corresponding values were 3972.72, 4576.82, 3748.52, and 3672.23 kcal/kg for Argentina corn (P > 0.05); 5066.33, 5015.84, 3521.38, and 3925.40 kcal/kg for domestic corn (P < 0.05); 2636.41, 4237.58, 2190.01, and 2010.96 kcal/kg for soybean meal (P < 0.01); and 6874.27, 7544.62, 8726.15, and 7281.17 kcal/kg for soybean oil (P > 0.05). In conclusion, the regression model using a high proportion of cellulose was not suitable for estimating the apparent metabolizable energy concentration of glucose. The substitution method showed that feed ingredients differed in stage-dependent apparent metabolizable energy concentration in broilers. When metabolizable energy values are established using the substitution method, dry matter digestibility, energy digestibility, and dietary apparent metabolizable energy differences should be considered together to improve the application of ingredient energy values in phase-feeding programs for broilers.