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FIBER IN RUMINANT DIETS

FIBER IN RUMINANT DIETS. Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. Fiber includes cellulose, hemicellulose , lignin, and soluble fiber ( fructans , pectans , galactans , and beta- glucans ).

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FIBER IN RUMINANT DIETS

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  1. FIBER IN RUMINANT DIETS

  2. Fiber can be defined as carbohydrates not digested by mammalian enzymes but can be digested by rumen microorganisms. • Fiber includes cellulose, hemicellulose, lignin, and soluble fiber (fructans, pectans, galactans, and beta-glucans). • Most fiber in plant material is found in the structural components of cell walls.

  3. Ruminant livestock (cattle, goats, and sheep) can use large amounts of forage with high fiber content. • Fiber-digesting bacteria digest structural carbohydrates in the rumen into VFA, which is as main energy source for ruminant.

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

  5. Ruminant fiber requirementEffects of fiber on ruminant intake, digestion and metabolism • 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 digestion Effective fiber is the NDF remaining on a 1.18 screen, as a % of total DM eNDFpH% of maximum fiber digestion 24 6.4 98 20 6.3 95 16 6.1 87 12 5.9 70 8 5.7 28 4 5.6 0

  6. 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

  7. 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 80 40 Acetate Propionate Molar % Lactate 7 6 5 pH

  8. 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 60:4040:6020:80 VFAs, 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

  9. 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 ratio Item60:4040:6020:80 ME intake, Mcal 36.12 36.42 34.87 Energy balance, Mcal, RE 11.94 12.63 12.16 Milk energy, Mcal, LE 13.94 13.17 10.41 LE/RE x 100 117 104 86 Tissue energy, Mcal -2.00 -.54 1.75 Milk fat, % 3.5 3.0 2.7 Acetate/Propionate 3.32 2.57 2.00 70 40 10 Milk Milk or body weight Synthesis, kcal / 100 Kcal ME above maintenance Body tissue 30 40 50 60 70 Acetic acid, % of total VFA

  10. Cause for difference in energy partitioning Old theory Decreasing [Acetate] and increasing [Propionate] reduces milk fat synthesis and increases body tissue synthesis Basis: Propionate is needed to synthesize glucose Glucose needed for acetate metabolism for energy and fat synthesis Glucose stimulates insulin secretion Insulin increases glucose uptake by adipose and muscle tissue, but not mammary tissue Results in acetate being preferentially used by adipose and muscle tissue Current theory Reduced pH increases production of trans-10, cis-12 conjugated linoleic acid from polyunsaturated fatty acids Trans-10, cis-12 conjugated linoleic acid inhibits long chain fatty acid synthesis in the mammary gland (decreases)

  11. Microbial yield Inadequate dietary fiber Decreased salivary buffers Decreased pH Decreased osmotic pressure Decreased liquid turnover Decreased efficiency of microbial growth eNDFTheoretical maximum microbial synthesis, g/g CHO fermented 24 .40 20 .40 16 .36 12 .32 8 .28 4 .24

  12. 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 40 kg milk 20 kg milk 4 3 2 DMI, % BW Physical limitation Physiological control 20 30 40 50 NDF, % DM

  13. 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 microorganisms Dilutes VFAs Increases liquid turnover Motility

  14. 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

  15. Displaced abomasum Decreased fiber Muscle atrophy Subclinical acidosis Decreased feed intake Empty abomasum Displaced abomasum

  16. The fiber requirements of ruminant animals • 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

  17. 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 NDF NDFADFCF r TDN .65 .76 .80 Rate of digestion is important at high feed intakes NDF is more highly related to feed volume than CF or ADF NDFADFCF r Feed volume .78 .62 .71 NDF is more highly related to chewing time than CF or ADF NDFADFCF r Chewing time .86 .73 .76

  18. 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 eNDF Feed% NDF% of NDF% of DM Corn cobs 87 56 49 Cracked corn 10.8 60 6.7 Whole corn 9.0 100 9.0 Corn gluten feed 36.0 36 12.8 Corn silage 41.0 71 29 Alfalfa haylage (1/4” cut) 43.0 67 29 Alfalfa hay, late vegetative 37.0 92 34 Oat straw 63.0 98 62 Bromegrass 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

  19. Current fiber requirements Beef cattle Minimum eNDF, % DM High concentrate diets to maximize 5 – 8 Gain/Feed, good bunk management & ionophore Mixed diet, variable bunk management or 20 no ionophore High concentrate diet to maximize 20 non-fiber carbohydrate (NFC) use & microbial yield

  20. 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) ForageDiet Minimum NDF, %DMMinimum NDF, %DMMaximum 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

  21. Additional recommendations for dairy cattle % of diet DM Nonstructural carbohydrates 30-40 Non-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 Assumptions Forage supply 70 to 80% of the NDF Forages 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 28 Peak lactation 25

  22. Use of buffers in ruminant diets • Functions of buffers • Increase ruminal pH • Maintain DM intake • Prevent acidosis • Increase liquid turnover • Buffers commonly used BufferAdditional effectsPreventative level Sodium bicarbonate - 1.2 to 1.6% of grain .75% of diet Sodium sesquicarbonate - .3 to .75 lb/d Magnesium oxide Increase uptake .4 to .5% of grain of acetate by mammary gland .1 to .2 lb/d Potassium carbonate Provides potassium .5 to .9 lb/d

  23. 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

  24. Neutral detergent fiber (NDF) = • fiber that is insoluble in neutral detergent and includes cellulose, hemicellulose, and lignin. • represents all plant cell wall material, is only partly digestible by animals, and • is negatively correlated with dry matter intake. As NDF increases in the diet, dry matter intake decreases.

  25. Acid detergent fiber (ADF) = • is the portion of fiber that is insoluble in acid detergent (cellulose and lignin), • is composed of highly indigestible plant material, generally only the lignified or otherwise undigestible portions of plant cell walls. • is negatively correlated with digestibility. Generally, as ADF increases, forages or feeds become less digestible.

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