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Using Digestible NDF to Determine Forage Quality

Using Digestible NDF to Determine Forage Quality Dr. Dan Undersander University of Wisconsin Importance of Digestible Fiber Use of empirical equations For many years we estimated forage energy content from single analyte Sampling of Empirical equations From Western Region

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Using Digestible NDF to Determine Forage Quality

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  1. Using Digestible NDF to Determine Forage Quality Dr. Dan Undersander University of Wisconsin

  2. Importance of Digestible Fiber • Use of empirical equations • For many years we estimated forage energy content from single analyte

  3. Sampling of Empirical equations • From Western Region • %TDN = 82.38 - (0.7515 x ADF) • From Pennsylvania • %TDN = 4.898 + (89.796 x NEL) • NEL (Mcal/lb) = 1.044 - (0.0119 x ADF) • From Midwest • %DDM = 88.9 - (0.779 x ADF)

  4. TDN Estimates from Different Empirical Equations

  5. Relationship of digestible fiber to ADF for Alfalfa

  6. Relationship of NDF digestibility to NDF Content

  7. NRC (2001) Dairy Approach to Predicting TDN of Forages • Uniform feed fractions will have predictable digestion coefficients TDN 1-X =tdCP + (tdFAx 2.25) + tdNDF + tdNFC -7 • A more accurate and robust way to estimate TDN of forages than ADF • TDN values estimated by NRC(2001) are different than what we are used to.

  8. Influence of NDF digestibility on forage digestibility TDN = tdCP + (tdFA x 2.25)+ (.75 x NDFD48 x NDF)+ tdNFC -7 NDF ADF NDFD48TDN DDM* Forage A: 40 30 5861.6 65.5 Forage B: 40 30 3653.6 65.5 *DDM = 88.9 * .779(ADF)

  9. Influence of NDF digestibility on dry matter intake dIntake = base intake plus adjustment for dNDF = base intake + (NDFD-average NDFD) * .374) Oba and Allen, 1999. J. Dairy Sci. 82:589-596 NDF ADF NDFDdIntake DMI* Forage A 40 30 5831.0 2.78% of BW Forage B 40 30 3622.8 2.78% of BW *DMI = 120/NDF

  10. Adjusting DMI, Base TMR Lb DM Alfalfa 20-30-40-58 25 Corn silage 6 HMC 20 Protein/mineral/vitamins 7 DMI 58 NRC 2001 ration evaluation (110 lb milk) NE allowable milk, lb 93 MP allowable milk, lb 110 NEl balance, Mcal - 5.6 TMR Nel, Mcal/lb .70

  11. Suppose alfalfa composition changed to 20-30-40-36: Impact: TDN 61.6 -> 53.6 dIntake 31.0 ->22.8 Action steps Change alfalfa TDN in ration program Discount TMR intake .374(58-36) = 8 lb Adjusting DMI, Base TMR Lb DM Alfalfa 20-30-40-58 25 Corn silage 6 HMC 20 Protein/mineral/vitamins 7 DMI 58 NRC 2001 ration evaluation NE allowable milk, lb 93 MP allowable milk, lb 110 NEl balance, Mcal - 5.6 TMR Nel, Mcal/lb .70

  12. Adjusting DMI and TDN Base TMR Adjusted TMR 20-30-40-58 20-30-40-36 Alfalfa 25 22 Corn silage 6 5 HMC 20 17 Protein/mineral/vitamins 7 6 DMI 58 50 NRC 2001 ration evaluation NE allowable milk, lb 93 83 MP allowable milk, lb 110 91 NEl balance, Mcal - 5.6 -8.7 TMR Nel, Mcal/lb .70 .73

  13. Relative Feed Value = (Intake Potential * Digestible DM) Constant

  14. Relative Feed Value (Current) Intake Potential = 120/NDF Digestible DM = 88.9 - (0.779*ADF) Constant = 1.29

  15. Relative Feed Value (Current) Intake Potential = 120/NDF Digestible DM = 88.9 - (0.779*ADF) Constant = 1.29

  16. Relative Forage Quality (RFQ) = (dIntake Potential * dTDN) Constant

  17. Relative Forage Quality Intake potential = base intake plus adjustment for dNDF = base intake + ((dNDF-average dNDF) *.374) =(0.012/NDF) + (NDFD-45)*0.374*1350/100 From Oba and Allen, 1999, J Dairy Sci

  18. Relative Forage Quality Total Digestible Nutrients (dTDN) = dNFC + dCP + dFA*2.25 + dNDF - 7 = [(NFC*.98) + (CP*.93) + (FA*.97*2.25) + NDF * NDFD] - 7 From NRC, 2001

  19. Relative Forage Quality (RFQ) RFQ = dIntake potential*dTDN 1.23

  20. Dissatisfied Customers

  21. Giving Energy Away Dissatisfied Customers

  22. Relationship of RFV to RFQ in Alfalfa, World’ s Forage Superbowl, 2003 Above line – * energy not valued Below line – * poor animal performance * dissatisfied customers * heat damaged samples

  23. Summary • Digestible fiber more accurately predicts animal performance on forage than ADF. • RFQ uses TDN and digestible fiber. • RFQ will more accurately index value of hay to animals.

  24. Forage quality of alfalfa in Kawas trial From Kawas et al. 1989

  25. Effect of forage quality on dry matter intake

  26. Effect of forage quality on 4% fat corrected milk at four concentrate levels From Kawas et al. 1989

  27. Effect of forage quality on butterfat content of milk at four concentrate levels From Kawas et al. 1989

  28. Value of milk from forage quality From Kawas et al. 1989

  29. Value of high quality hay • Increased energy content • Increased intake • Use above 150 RFQ to mix with low quality • Values low quality forage that may be on hand • May be difficult to mix two hays in some operations • Use above 150 RFQ to mix with corn silage • Value to protein because corn silage is lower in protein • Value to low NDF because corn silage is higher in fiber

  30. Further Information www.uwex.edu/ces/forage

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