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 = 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

Dry sieving peNDF 1.18 and FCM/DMI (Grant, 2008, unpublished)  12 studies using vertical dry sieving (standard procedure)

How well does peNDF system work? (Zebeli et al., 2006) 33 experiments, Chewing activity peNDF R 2 =0.44 (0.76, Mertens) Ruminal pH peNDF R 2 =0.67 NDF digestibility peNDF R 2 =0.56

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?

NDFTotal Chewing Activity Feed% of DM(min/kg of DM)(min/kg of NDF) Alfalfa Dried grass Ryegrass Grass Ryegrass Grass Oat straw Oat straw Oat straw Chewing and NDF source (Mertens, 1997)

Straw is “concentrated” chewing source Item52%47%43%39% Corn silage Alfalfa-grass silage Wheat Straw peNDF, % TCT, min/d TCT, min/kg NDF intake (Meyers et al., 2009)

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

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)

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by ball milling forages (Cotanch et al., 2007)  Ball mill with ceramic balls mimics chewing action (Jim Welch, unpublished data)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 cut Corn silage Corn silage Grass Hay 1 st cut Wheat Straw Alfalfa Hay Stems Alfalfa Hay Leaves 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) 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 Corn st Cut Hay6.1 (3.6 lb)0.0 Straw (3.0 lb) Concentrate mix NDF, % of DM pef of TMR 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 Behavior response Eating, min/d Ruminating, min/d479505* Performance response DMI, lb/d Protein yield, lb/d Fat yield, lb/d *

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 silage BMR corn silage Haycrop silage15.0 Crude protein, % of DM peNDF, % of DM Digested starch, % of DM DMI, % of BW * SCM, kg/d * SCM/DMI, kg/kg * TCT, min/kg NDFI10083* Average pH *

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 pef h NDFD, % Fragility Chewing response, min/d  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

pef adjustment factor: grass 24-h NDFD FragilityAdjustment factor

pef adjustment factor: corn silage 24-h NDFD FragilityAdjustment factor

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

Thank you…