Particle Size, Fiber Digestibility, Fragility, and Chewing Response

in Dairy CattleRick GrantRick Grant

W. H. Miner Agricultural Research InstituteW. H. Miner Agricultural Research InstituteChazy, NYChazy, 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Dry sieving peNDF1.18 and FCM/DMI (Grant, 2008, unpublished)

0.6

0.9

1.2

1.5

1.8

10 15 20 25 30 35 40peNDF1.18 (% of DM)

FCM

/DM

I (kg

/kg)

12 studies using vertical dry sieving (standard procedure)

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

peNDF R2=0.56

Recurring question: can we improve on peNDF system?Is there any value in doing so?

Does all NDF at the sameparticle size elicit the the same chewing response?

NDF Total Chewing ActivityFeed % of DM (min/kg of

DM)(min/kg of

NDF)Alfalfa 49 61 125Dried grass 51 63 123Ryegrass 65 90 139Grass 65 103 158Ryegrass 68 104 152Grass 65 107 165Oat straw 78 163 209Oat straw 79 143 181Oat straw 84 164 195

Chewing and NDF source (Mertens, 1997)

Straw is “concentrated” chewing source

Item 52% 47% 43% 39%

Corn silage 37.3 34.0 31.0 27.9Alfalfa-grass silage 14.5 11.1 5.9 0.6

Wheat Straw - 2.1 6.2 10.3peNDF, % 21.5 20.2 19.2 18.9TCT, min/d 783 780 772 774TCT, min/kg NDF intake 94 92 93 91

(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Ball mill with ceramic balls mimics chewing action (Jim Welch, unpublished data)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

(pefi – pefBM15)/pefi x 100%

Ranges from 0 (very tough) to 100 (very fragile)

Forage

NDFD24

Original

pef

30-min BMpef

% chang

eGrass silage 1st cut 55.8 60.1 39.3 -34.5

Corn silage 1 42.8 92.0 67.0 -27.2Corn silage 2 35.4 88.9 67.5 -24.1

Grass Hay 1st cut 29.6 84.1 63.1 -25.0Wheat Straw 21.5 99.7 84.8 -14.9

Alfalfa Hay Stems 28.1 95.0 71.6 -24.6Alfalfa Hay Leaves 47.6 41.1 13.0 -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 NDFd24

(Cotanch et al., 2007)

BMRs

Straws

2030405060708090

20 30 40 50 60NDFD24

% C

hang

e in

pef

"Fra

gilit

y"

NDFd24 versus fragility for grass hays: effect on chewing response

31% NDFD46% Fragility0.13 pef

55% NDFD81% Fragility0.15 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 Diet Straw DietHaycrop silage 14.0 14.0Corn Silage 17.7 17.7BMR Corn 15.2 15.21st Cut Hay 6.1 (3.6 lb) 0.0Straw 0.0 5.1 (3.0 lb)Concentrate mix 47.0 48.0NDF, % of DM 34.3 33.8pef of TMR 0.66 0.67peNDF 22.6 22.6

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

DietHay

(3.6 lb)Straw (3.0 lb)

Chemical composition of forages24-h NDFD %Fragility %

pef

3383

0.52

2234

0.53Behavior response

Eating, min/d 250 249Ruminating, min/d 479 505*

Performance responseDMI, lb/d

Protein yield, lb/dFat yield, lb/d

623.53.6

623.5

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)

Conventional BMRConventional corn silage 43.3 ---

BMR corn silage --- 43.3Haycrop silage 15.0 15.0

Crude protein, % of DM 17.0 17.4peNDF, % of DM 19.2 19.5

Digested starch, % of DM 25.0 22.8DMI, % of BW 3.42 3.75*

SCM, kg/d 37.7 39.7*SCM/DMI, kg/kg 1.49 1.42*

TCT, min/kg NDFI 100 83*Average pH 6.08 5.95*

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

020406080

100120

0 20 40 60 80

NDFD24 %

Frag

ility

%

BMRCS CS HCS SGS Straw

Some practical feeding management considerations . . .

Agri-ChopperAgri-ChopperUses knives to chop Uses knives to chop hayhay

HaybusterHaybusterUses hammer mill with Uses hammer mill with screenscreen

Agri-chopper Haybuster

Type of forage chopper can make a difference

Agri-Chopper HaybusterMeasure Grass

hayWheat straw

Grass

hay

Wheatstra

wpef 0.72 0.80 0.72 0.8424-h NDFD, % 21.3 19.3 31.8 25.0Fragility 19 18 27 23Chewing response, min/d

740 750 700 710

Don’t assess choppers entirely on particle size

Develop adjustment factors for pef

CPM-Dairy 3.0

pef adjustment factor: grass24-h NDFD Fragility Adjustment

factor30 50 0

40 60 -6

50 70 -10

60 80 -19

pef adjustment factor: corn silage24-h NDFD Fragility Adjustment

factor30 65 0

40 75 -7

50 85 -13

60 95 -20

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

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…