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Tính toán các giá trị năng lượng của thức ăn Giá trị GE: Để tính giá trị GE của các loại thức ăn vùng nhiệt đới dùng công thức của Jarige (1978); Xande và cs. (1989b): GE (kcal/kg OM) = 4543 + 2,0113 x CP (g/kg OM) ± 32,8 (r = 0,935) Trong đó GE = Kcal/kg chất hữu cơ - OM Sau đó chuyển giá trị này thành GE: Kcal/kg chất khô - DM và MJ/kg DM Giá trị DE: Để tính giá trị DE dùng công thức của Jarige (1978); Xande và cs. (1989b): DE = GE x dE Ở đây: DE = Kcal/kg OM. dE - Tỷ lệ tiêu hoá của năng lượng thô = 1,0087 dOM - 0,0377 ± 0,007 (r = 0,996) dOM: tỷ lệ tiêu hoá của chất hữu cơ. Sau đó chuyển giá trị này thành DE: Kcal/kg DM và MJ/kg DM. Giá trị ME: Để tính giá trị ME của thức ăn nhiệt đới dùng công thức của Jarige (1978); Xande và cs. (1989): ME = DE x ME/DE Trong đó: ME = Kcal/kg OM. Sau đó chuyển giá trị này thành ME: Kcal/kg DM và MJ/kg DM. ME/DE = 0,8417 - (9,9 x 10-5 x CF [crude fibre - xơ thô (g/kg chất hữu cơ]) - (1,96 x 10-4 x CP (crude protein-protein thô) (g/kg chất hữu cơ)) + 0,221 x NA). NA = Số lượng chất hữu cơ tiêu hoá ăn được (Digestible oganic matter - DOM) (g/kg W0,75)/23 . Thông thường người ta sử dụng giá trị bình quân: NA = 1,7 131 Giá trị NE Để tính giá trị NE của thức ăn nhiệt đới dùng công thức của Jarige (1978); Xande và cs. (1989b): NE = ME × kl kl = 0,463 + [0,24 × (ME/GE)] kl: là hiệu quả sử dụng năng lượng trao đổi cho sản xuất sữa Năng lượng thuần cũng có thể biểu diễn dưới dạng đơn vị thức ăn. Theo hệ thống đánh giá giá trị thức ăn của Pháp, đơn vị thức ăn tạo sữa (UFL) của thức ăn được tính bằng 1700 Kcal NE. UFL = NE (Kcal)/1700 2. Tính toán các giá trị protein của thức ăn Giá trị protein của một thức ăn là tổng lượng protein được tiêu hoá tại ruột non tính bằng g/kg vật chất khô (PDI)- Protéines Digestibles dans l’Intestine) và được biểu thị bằng hai giá trị PDIE và PDIN. Thông thường người ta lấy giá trị thấp hơn trong hai giá trị này làm giá trị PDI của thức ăn, một thức ăn có hai giá trị này tương đương nhau là một thức ăn cân đối). Protein tiêu hóa ở ruột (PDI) (g/kgDM): - Protein tiêu hoá ở ruột giới hạn bởi năng lượng: PDIE = PDIA + PDIME - Protein tiêu hoá ở ruột giới hạn bởi ni tơ: PDIN = PDIA + PDMN và được tính như sau: PDIME (g/kgDM): Số lượng protein vi sinh vật tiêu hoá ở ruột có thể được tổng hợp khi năng lượng dễ lên men không bị hạn chế: PDIME = 135 x 0,8 x 0,7xDOM (kg/kgDM) Ở đây: DOM - Chất hữu cơ tiêu hoá ((kg/kg vật chất khô) = OM (chất hữu cơ) kg/kg DM (chất khô) x Tỷ lệ tiêu hoá OM (chất hữu cơ) PDIMN (g/kgDM): Số lượng protein vi sinh vật tiêu hoá ở ruột có thể được tổng hợp khi năng lượng không bị hạn chế: PDIMN = CP (g/kgDM) x (S + 0,35 x (1-S)) x 0,8 x 0,7 S: độ hoà tan của Nitơ ≅ 0,3 cho các loại thức ăn. PDIMN (g/kg DM) = CP (g/kgDM) x (0,3 + 0,35 x (1-0,3)) x 0,8x0,7 PDIA (g/kgDM): Protein tiêu hoá ở ruột từ nguồn thức ăn ăn vào (g/kgDM). PDIA (g/kgDM) = 0,65x CP (g/kgDM) x (1-S) x dr 132 Ở đây: dr: Tỷ lệ tiêu hoá của protein của khẩu phần trong ruột. dr = (0,65 x Protein không hoà tan (g/kg DM) - PANDI)/0,65 x Protein không hoà tan (g/kgDM) Protein không hoà tan = CP x (1-S) PANDI (g/kgDM): Protein của khẩu phần không tiêu hoá ở ruột non PANDI (g/kgDM) = ICP - 0,501 - 0,033 x DOM - 0,009 x IDOM = 0,045 x CP. ICP: Protein không thể tiêu hoá ICP = 0,501 + 0,045 CP g/kgDM) + 0,033 DOM (g/kg DM) + 0,009 IDOM (chất hữu cơ không thể tiêu hoá, g/kgDM) Ở đây: * Protein tiêu hoá DCP = CP (g/kgDM) x tỷ lệ tiêu hoá của CP * Chất hữu cơ tiêu hoá DOM (g/kgDM) = OM (g/kgDM) x tỷ lệ tiêu hoá OM * Chất hữu cơ không thể tiêu hoá IDOM (g/kgDM) = OM (g/kgDM) - DOM (g/kgDM) 133 PHỤ LỤC 2 1. 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