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Particle Size, Fiber Digestibility, Fragility, and Chewing Response in Dairy Cattle

Particle Size, Fiber Digestibility, Fragility, and Chewing Response in Dairy Cattle. Rick Grant W. H. Miner Agricultural Research Institute Chazy, NY. pef and peNDF: quick review. pef = p hysical e ffectiveness f actor % of sample retained on ≥ 1.18-mm screen when dry sieved

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Particle Size, Fiber Digestibility, Fragility, and Chewing Response in Dairy Cattle

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  1. Particle Size, Fiber Digestibility, Fragility, and Chewing Response in Dairy Cattle Rick Grant W. H. Miner Agricultural Research Institute Chazy, NY

  2. pef and peNDF: quick review • pef = physical effectiveness factor • % of sample retained on ≥1.18-mm screen when dry sieved • peNDF = physically effective NDF • peNDF = pef x NDF% • Based entirely on particle size

  3. Dry sieving peNDF1.18 and FCM/DMI (Grant, 2008, unpublished) • 12 studies using vertical dry sieving (standard procedure)

  4. How well does peNDF system work? (Zebeli et al., 2006) • 33 experiments, 1997-2005 • Chewing activity • peNDF R2=0.44 (0.76, Mertens) • Ruminal pH • peNDF R2=0.67 • NDF digestibility • peNDFR2=0.56

  5. Recurring question: can we improve on peNDF system? • Is there any value in doing so? • Does all NDF at the same • particle size elicit the • the same chewing response?

  6. Chewing and NDF source (Mertens, 1997)

  7. Straw is “concentrated” chewing source (Meyers et al., 2009)

  8. Why differences in chewing response? • Forage Fragility Concept • Forage fibers differ in tensile strength, or toughness, and resistance to physical breakdown during chewing • Particles differ in • Diameter • Lignin & lignin linkages • Moisture • Digestibility

  9. Forage Fragility • How to measure forage fragility in the lab? • Artificial mastication (Troelson and Bigsby, 1964) • Comminution energy required to grind • Shear-force energy required to cut • Ball mill: particle size reduction index

  10. Ball mill method for measuring forage fragility • Equipment • Ball mill • Jars: 5.5-L • Ceramic cylinders (balls): 2.6-L • Milling time: 15 min at 80 rpm • Ro-Tap: dry vertical sieving apparatus (1.18-mm sieve)

  11. Measuring “fragility” by ball milling forages (Cotanch et al., 2007) • Ball mill with ceramic balls mimics chewing action (Jim Welch, unpublished data)

  12. Measurement of fragility • Fragility determined as Δpef (pefi – pefBM15)/pefi x 100% • Ranges from 0 (very tough) to 100 (very fragile)

  13. pef values of original sample and ball milled sample with % decrease in pef value (fragility) (Cotanch et al., 2007)

  14. Forage fragility as measured by % change in pef plotted by NDFd24 BMRs Straws (Cotanch et al., 2007)

  15. NDFd24 versus fragility for grass hays: effect on chewing response 30-60 min/d TCT 55% NDFD 81% Fragility 0.15 pef 31% NDFD 46% Fragility 0.13 pef (Cotanch et al., 2008)

  16. Magnitude of Lactation Responses to Varying Forage Fragility and NDFD -Hay versus straw -BMR corn silage

  17. Grass hay versus straw: how different are they in stimulating chewing?What does the cow say?

  18. Materials and methods: diets and feeding

  19. Response to supplemental NDF at similar particle size (Miner Inst., 2009)

  20. Fragility of BMR versus Conventional Corn Silage • Usually approximately 10%-units greater in NDF digestibility • BMR has 6 to 31% greater fragility than conventional silages as measured with ball milling technique

  21. Fragility of BMR versus Conventional Corn Silage (unpublished, 2010)

  22. Rumen pH for cows fed bmr or conventional corn silages in TMR • Particle size does not tell entire story!

  23. Fragility field study: Fragility x 24-h NDFD: Combined forages, 2009

  24. Some practical feeding management considerations . . .

  25. Agri-Chopper • Uses knives to chop hay • Haybuster • Uses hammer mill with screen Agri-chopper Haybuster

  26. Type of forage chopper can make a difference • Don’t assess choppers entirely on particle size

  27. Develop adjustment factors for pef CPM-Dairy 3.0

  28. pef adjustment factor: grass

  29. pef adjustment factor: corn silage

  30. Implications for Ration Formulation • High NDFD, high fragility forages stimulate less chewing per unit of NDF at similar particle size • Need to • Feed more total forage • Formulate for higher peNDF • Use pef adjustment factor • Supplement with lower NDFD, lower fragility forages • Grass, straw

  31. Conclusions • NDFD and fragility are related • Can improve our prediction of chewing and performance response • Focus on NDFD • Assessment of forage physical properties shouldn’t stop with a simple particle size measurement

  32. Thank you…

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