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
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
Measuring “fragility” by ball milling forages (Cotanch et al., 2007) Ball mill with ceramic balls mimics chewing action (Jim Welch, unpublished data)
Measurement of fragility Fragility determined as Δpef (pef i – pef BM15 )/pef i x 100% Ranges from 0 (very tough) to 100 (very fragile)
Forage NDFD 24 Original pef 30-min BM pef % change Grass silage 1 st cut55.860.139.3-34.5 Corn silage 142.892.067.0-27.2 Corn silage 235.488.967.5-24.1 Grass Hay 1 st cut29.684.163.1-25.0 Wheat Straw21.599.784.8-14.9 Alfalfa Hay Stems28.195.071.6-24.6 Alfalfa Hay Leaves47.641.113.0-68.5 pef values of original sample and ball milled sample with % decrease in pef value (fragility) (Cotanch et al., 2007)
Forage fragility as measured by % change in pef plotted by NDFd 24 (Cotanch et al., 2007) BMRs Straws
NDFd 24 versus fragility for grass hays: effect on chewing response 31% NDFD 46% Fragility 0.13 pef 55% NDFD 81% Fragility 0.15 pef (Cotanch et al., 2008) 30-60 min/d TCT
Magnitude of Lactation Responses to Varying Forage Fragility and NDFD -Hay versus straw -BMR corn silage
Grass hay versus straw: how different are they in stimulating chewing? What does the cow say?
Materials and methods: diets and feeding Ingredients (% DM)Hay DietStraw Diet Haycrop silage14.0 Corn Silage17.7 BMR Corn15.2 1 st Cut Hay6.1 (3.6 lb)0.0 Straw0.05.1 (3.0 lb) Concentrate mix47.048.0 NDF, % of DM34.333.8 pef of TMR0.660.67 peNDF22.6
Response to supplemental NDF at similar particle size (Miner Inst., 2009) Diet Hay (3.6 lb) Straw (3.0 lb) Chemical composition of forages 24-h NDFD % Fragility % pef 33 83 0.52 22 34 0.53 Behavior response Eating, min/d250249 Ruminating, min/d479505* Performance response DMI, lb/d Protein yield, lb/d Fat yield, lb/d 62 3.5 3.6 62 3.5 3.9*
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
Fragility of BMR versus Conventional Corn Silage (unpublished, 2010) ConventionalBMR Conventional corn silage43.3--- BMR corn silage---43.3 Haycrop silage15.0 Crude protein, % of DM17.017.4 peNDF, % of DM19.219.5 Digested starch, % of DM25.022.8 DMI, % of BW3.423.75* SCM, kg/d37.739.7* SCM/DMI, kg/kg1.491.42* TCT, min/kg NDFI10083* Average pH6.085.95*
Rumen pH for cows fed bmr or conventional corn silages in TMR Particle size does not tell entire story!
Fragility field study: Fragility x 24-h NDFD: Combined forages, 2009
Some practical feeding management considerations...
Agri-Chopper Uses knives to chop hay Haybuster Uses hammer mill with screen Agri-chopper Haybuster
Type of forage chopper can make a difference Agri-ChopperHaybuster MeasureGrass hay Wheat straw Grass hay Wheat straw pef0.720.800.720.84 24-h NDFD, %21.319.331.825.0 Fragility19182723 Chewing response, min/d 740750700710 Don’t assess choppers entirely on particle size
In situ digestion (24 h) and fragility of 2-inch particles Function of microbial digestion and fungal hyphae penetrating cracks in cell wall, stomata, etc. (Van Soest, 2009) Conventional CS ControlIn situ 4658 BMR corn silage ControlIn situ 5364 Grass hay ControlIn situ 6475
Develop adjustment factors for pef CPM-Dairy 3.0
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
Potential application of fragility measurement? Models that predict particle flow from the rumen are sensitive to rate of large particle breakdown Rate of forage particle reduction Measured between 3.4 and 7.1%/h (Ulyatt, 1983; Woodford and Murphy, 1988) Similar to rate of particle breakdown with ball milling
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
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