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FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes...

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FIBER IN RUMINANT DIETS
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Page 1: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

FIBER IN RUMINANT DIETS

Page 2: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms.

o Fiber includes cellulose, hemicellulose, lignin, and soluble fiber (fructans, pectans, galactans, and beta-glucans).

o Most fiber in plant material is found in the structural components of cell walls.

Page 3: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

o Ruminant livestock (cattle, goats, and sheep) can use large amounts of forage with high fiber content.

o Fiber-digesting bacteria digest structural carbohydrates in the rumen into VFA, which is as main energy source for ruminant.

Page 4: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Rumen changes in response to decreased fiber intake (Adapted from Trenkle, 2002)

Page 5: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Digestibility Inadequate fiber

Results in reduced fiber digestion Cause

Maximum growth of cellulolytic bacteria and protozoa occurs between pH 6 and 7

If the effective fiber concentration of the diet is < 24.5%, rumen pH will decrease resulting in reduced fiber digestionEffective fiber is the NDF remaining on a 1.18 screen, as a % of total DM

eNDF pH % of maximum fiber digestion

24 6.4 9820 6.3 9516 6.1 8712 5.9 70 8 5.7 28 4 5.6 0

Page 6: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Physiological cause for the inhibition of cellulolytic bacteria ATP energy production from the proton motive

force across the cell membrane is inhibited by acids entering the cells

Inadequate quantities of HCO3- which is the active

form of CO2 for anerobic bacteria Toxicity of the VFAs and lactate is greater because

nonionized forms more readily cross cell membranes

Reduced ruminal turnover reduces efficiency of microbial growth

Excess fiber If lignified, high levels of fiber may reduce DM

digestibility because soluble constituents are diluted or the ratio of soluble nutrients to the insoluble ones is low

Page 7: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Fermentation endproducts Volatile fatty acids

Decreased fiber causes reduced pH which causes Increased production of total VFAs Decreased molar proportions of acetate and butyrate Increased molar proportions of propionate

Acetate

Propionate

Lactate

7 6 5 pH

Molar %

80

40

Page 8: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Cause of changes in VFAs Primary end-products of cellulolytic bacteria (pHopt6-7)

Acetic acid Butyric acid Carbon dioxide Hydrogen

Primary end-products of amylolytic bacteria (pHopt5-6) Acetic acid Propionic acid Lactic acid

Hay:Concentrate 60:40 40:60 20:80VFAs, molar % Acetic acid 66.9 62.9 56.7 Propionic acid 21.1 24.9 30.9 Butyric acid 12.2 12.2 12.4

Page 9: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Effects of changes in VFA concentrations on efficiency of energy use for body tissue or milk synthesis Decreasing the concentration of acetate and increasing the

concentration of propionate will decrease the energetic efficiency of milk production while increasing that of body tissue synthesis

Hay:grain ratioItem 60:40 40:60 20:80ME intake, Mcal 36.12 36.42 34.87Energy balance, Mcal, RE 11.94 12.63 12.16Milk energy, Mcal, LE 13.94 13.17 10.41LE/RE x 100 117 104 86Tissue energy, Mcal -2.00 -.54 1.75Milk fat, % 3.5 3.0 2.7Acetate/Propionate 3.32 2.57 2.00

70

40

10

30 40 50 60 70Acetic acid, % of total VFA

Body tissue

MilkMilk or body weightSynthesis, kcal /100 Kcal ME above maintenance

Page 10: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Cause for difference in energy partitioning

Old theoryDecreasing [Acetate] and increasing [Propionate] reduces milk fat synthesis and increases body tissue synthesisBasis:

Propionate is needed to synthesize glucoseGlucose needed for acetate metabolism for

energy and fat synthesisGlucose stimulates insulin secretionInsulin increases glucose uptake by adipose

and muscle tissue, but not mammary tissueResults in acetate being preferentially used

by adipose and muscle tissue

Current theoryReduced pH increases production of trans-10, cis-12 conjugated linoleic acid from polyunsaturated fatty acidsTrans-10, cis-12 conjugated linoleic acid inhibits long chain fatty acid synthesis in the mammary gland (decreases)

Page 11: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Microbial yield Inadequate dietary fiber

Decreased salivary buffers

Decreased pH Decreased osmotic pressure

Decreased liquid turnover

Decreased efficiency of microbial growth

eNDF Theoretical maximum microbial synthesis, g/g CHO fermented

24 .40 20 .40 16 .36 12 .32 8 .28 4 .24

Page 12: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Feed consumption At high fiber levels, feed intake is limited by the

physical volume occupied by fiber

Physical limitation is freed by: Digestion Particle size reduction Passage

20 30 40 50 NDF, % DM

4

3

2

DMI, % BWPhysical limitation

Physiologicalcontrol

20 kg milk

40 kg milk

Page 13: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

At low fiber levels, feed intake is under physiological control Limitations

VFAs Increased [Acetate] in the rumen decreases feed intake Increased [Propionate] in the portal vein decreases feed

intake Hormones

Insulin Glucagon

Osmolality Increased [H+] in duodenum reduces reticuloruminal

contractions to reduce feed intake Acidosis a problem in feedlot cattle and dairy cows rapidly

changed from a high forage to a high grain diet Fiber’s role on low fiber diets

Saliva flow Provides buffers

Prevents undesirable microorganismsDilutes VFAsIncreases liquid turnover

Motility

Page 14: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Long-term health problems due to low fiber feeding Parakeratosis Liver abscess Laminitis Inadequate fiber

Decreased pH

Increased VFA and lactic acid

Decreased gram- bacteria

Release histamine and endotoxins (?)

Increased blood pressure

Dilation and damage to blood vessels

Page 15: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Displaced abomasum

Decreased fiber

Muscle atrophy Subclinical acidosis

Decreased feed intake

Empty abomasum

Displaced abomasum

Page 16: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Previous requirements Dairy

Before 1989 Minimum of 17% CF

1989 NRC Minimum of 21% ADF for first 3 weeks lactation period Minimum of 19% ADF at peak lactation

Beef Before 1996 NRC

Minimum of 10% roughage

Page 17: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Limitations of previous requirements CF and ADF do not represent all fiber fractions

CF contains variable amounts of cellulose and lignin ADF contains cellulose and lignin NDF contains cellulose, lignin, hemicellulose and pectins

While related to digestibility, CF and ADF are not as highly related to the rate of digestion as

NDFNDF ADF CF

rTDN .65 .76 .80 Rate of digestion is important at high feed intakes

NDF is more highly related to feed volume than CF or ADFNDF ADF CF

rFeed volume .78 .62 .71

NDF is more highly related to chewing time than CF or ADF

NDF ADF CF rChewing time .86 .73 .76

Page 18: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Fiber requirements have not considered the physical form of the fiber Physical form affects chewing time Particularly a problem with high fiber byproduct feeds To consider physical form, the Beef NRC used effective NDF

(eNDF) to express the fiber requirement of beef cattle Definition - % NDF remaining on a 1.18 mm screen after dry

sieving

eNDFFeed % NDF % of NDF % of DM

Corn cobs 87 56 49Cracked corn 10.8 60 6.7Whole corn 9.0 100 9.0Corn gluten feed 36.0 36 12.8Corn silage 41.0 71 29Alfalfa haylage (1/4” cut) 43.0 67 29Alfalfa hay, late vegetative 37.0 92 34Oat straw 63.0 98 62Bromegrass hay, pre-bloom 55.0 98 54

Relationship to rumen pH Rumen pH = 5.425 + .04229 x eNDF for eNDF < 35% DM

Doesn’t consider cation exchange capacity

Page 19: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Current fiber requirements Beef cattle Minimum

eNDF, % DMHigh concentrate diets to maximize 5 – 8Gain/Feed, good bunk management & ionophoreMixed diet, variable bunk management or 20no ionophoreHigh concentrate diet to maximize 20non-fiber carbohydrate (NFC) use & microbial yield

Page 20: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Lactating dairy cows Assumptions

Total mixed ration fed Adequate particle size of the forage Grain is corn

Recommendations (Adjusted for minimum forage NDF in diet DM)

Forage DietMinimum NDF, %DM Minimum NDF, %DM Maximum NFC, %

DM 19 25 44 18 27 42 17 29 40 16 31 38 15 33 36 Adjustments

Starch source High moisture corn 27% NDF (Minimum) Barley 27% NDF (Minimum)

Forage particle size Desire length of chop of forage at ¼”

15 to 20% of particles > 1.5” If mean particle size of forage decreases below 3 mm, then the

minimum dietary NDF % should be increased several percent Dietary buffers

Can lower NDF requirements Method of feeding

Feeding separate components will increase the NDF requirement

Page 21: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Additional recommendations for dairy cattle % of diet DMNonstructural carbohydrates 30-40Non-fiber carbohydrates 32-42

Merten’s approach to meeting the fiber requirements of dairy cattle Daily requirement for NDF in optimum ration is 1.2% of BW

AssumptionsForage supply 70 to 80% of the NDFForages are chopped at no less than ¼”

Allows the percentage of fiber in the diet to vary with milk production and feed intake

Recommended minimums % NDF

First 3 weeks 28Peak lactation 25

Page 22: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Functions of buffers Increase ruminal pH Maintain DM intake Prevent acidosis Increase liquid turnover

Buffers commonly usedBuffer Additional effects

Preventative levelSodium bicarbonate - 1.2 to

1.6% of grain .75

% of dietSodium sesquicarbonate - .3 to

.75 lb/dMagnesium oxide Increase uptake .4

to .5% of grain of acetate by mammary gland .1

to .2 lb/dPotassium carbonate Provides potassium .5

to .9 lb/d

Page 23: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Buffers are most effective when: Early lactation Switching from high forage to high grain diets Diet is deficient in effective fiber Concentrates and forages are fed separately Fermented forages are the only forage source

Particularly a problem with corn silage Large amounts of fermentable carbohydrates are fed at infrequent

intervals Small particle size or high moisture level of the grain Milk fat percentage of dairy cows is low

Milk fat % is .4 units < Protein % Milk fat % is < 2.5% in Holsteins

Off-feed problems caused by feeding rapidly fermenting feeds Heat stress

Limitations of buffers Unpalatable

2% sodium bicarbonate or 1% Magnesium oxide will reduce feed intake Responses are short-lived Buffers don’t cure all problems associated with low fiber diets

Displaced abomasum Health problems associated with buffers:

Bloat Urinary calculi Diarrhea

Page 24: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.
Page 25: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.
Page 26: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Neutral detergent fiber (NDF) =ofiber that is insoluble in neutral detergent and includes cellulose, hemicellulose, and lignin.

orepresents all plant cell wall material, is only partly digestible by animals, and

ois negatively correlated with dry matter intake. As NDF increases in the diet, dry matter intake decreases.

Page 27: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.
Page 28: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

Acid detergent fiber (ADF) =o is the portion of fiber that is insoluble in acid detergent (cellulose and lignin),

ois composed of highly indigestible plant material, generally only the lignified or otherwise undigestible portions of plant cell walls.

ois negatively correlated with digestibility. Generally, as ADF increases, forages or feeds become less digestible.

Page 29: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.
Page 30: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.
Page 31: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.
Page 32: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.
Page 33: FIBER IN RUMINANT DIETS. o Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. o Fiber.

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