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Saliva and the Fiber Requirements of Ruminants. Nutrient Requirements of Beef Cattle:Seventh Revised Edition:Update 2000. pp. 129-130. Available at: http://search.nap.edu/books/0309069343/html/

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saliva and the fiber requirements of ruminants

Saliva and the Fiber Requirements of Ruminants

Nutrient Requirements of Beef Cattle:Seventh Revised Edition:Update 2000. pp. 129-130. Available at: http://search.nap.edu/books/0309069343/html/

Nutrient Requirements of Dairy Cattle:Seventh Revised Edition, 2001. Chapter 4, pp. 34-42. Available at: http:search.nap.edu/books/0309069971/html/

Armentano, L. and M. Pereira. 1997. Measuring the effectiveness of fiber by animal response trials. J. Dairy Sci. 1416-1425

Available at: http://jds.fass.org/cgi/reprint/80/7/1416.pdf

Mertens, D. 1997. Creating a system for meeting the fiber requirements of dairy cows. J. Dairy Sci. 80:1463-1481.

Available at: http://jds.fass.org/cgi/reprint/80/7/1463.pdf

functions of saliva in ruminants
Functions of saliva in ruminants
  • Moistens and lubricates feeds
  • Water balance
  • Bloat prevention
  • Intake control
  • Recycling of nitrogen and minerals to the rumen
  • Buffering the rumen fermentation
  • Unlike nonruminants
    • No enzymes secreted in saliva of mature ruminants
slide3
Moistening and lubricating feed
    • Components responsible
      • Water
      • Mucin
    • Functions
      • Protects mucus membrane of mouth and esophagus
      • Aids in bolus formation
      • Water solubilizes soluble components providing access to taste buds
  • Water balance
    • 70% of the fluid entering the rumen
  • Bloat prevention
    • Mucin is a strong anti-foaming agent
  • Intake control (?)
    • Saliva infused into the abomasum increased reticular contractions and DM intake in sheep

Infused into the abomasum, ml/hr

Saliva:McDougall’s solution

0:1000250:750500:5000:1000

DMI, % BW 1.23 3.5 5.1 1.23

Reticular contractions, 1.4 5.7

% increase over no infusion

saliva s role in recycling n and minerals
Saliva’s role in recycling N and minerals
  • Nitrogen
    • In a 24 hour period, a 700 kg cow receiving a mixed hay:grain diet with secrete:
      • 190 l saliva
      • 30 to 80 gm total N
      • 50-130 gm urea
    • N recycling
      • Will be important on low protein diets
      • An important consideration in minimizing N excretion

Dietary protein

NPN

Protein

Metabolizable

protein

Microbial

protein

NH3

Urea

slide5
Amounts recycled
    • General estimates

% dietary N recycled = 15-20% (Approximately ½ as urea)

    • CNCPS program

% N recycled = (121.7 – 12.02 x %CP + .3235 x %CP2)/100

% CP in diet% N recycled

6 61

8 46

10 34

12 24

14 17

16 12

18 10

    • Marini et al. (2003)

Holstein heifers fed a corn meal-molasses- citrus pulp diet fed at 1.8 x maintenance

% CP in diet% N recycled

9.1 30

11.8 37

15.7 25

18.6 22

slide6
Routes of N recycling
    • Saliva
      • 15 to 50% of total recycled N
      • Factors
        • Blood urea concentration
        • Saliva flow
    • Gut wall
      • Major route
      • Factors
        • Increased ruminal [NH3]

Increases urea transferase which increases transfer of urea from blood to epithelium or vice versa

Decreases microbial urease activity of microbes adhered to the rumen wall:

decreases conversion on urea to NH3 needed to transfer NH3 across rumen wall

        • Decreased ruminal pH

Converts NH3 to NH4+ in the rumen

Only NH3 can cross the rumen wall

    • Marini et al. (2003)

% CPN recycled (saliva)N recycled (Gut wall)

g/d% of totalg/d% of total

9.1 0.8 3.0 25.1 97.0

11.8 1.5 3.6 39.6 96.4

15.7 3.8 10.4 32.7 89.6

18.6 5.4 13.7 33.9 86.3

slide7
Minerals
    • 700 kg cow producing 190 l saliva/day will secrete:
      • 1100 gm NaHCO3
      • 350 gm Na2 HPO4
      • 100 gm NaCl
    • Minerals recycled in saliva
      • Na
      • P
      • S
classes of salivary glands
Classes of salivary glands
  • Serous glands
    • Include:
      • Parotid glands
      • Inferior molar glands
    • Properties
      • Saliva is quite fluid
        • Parotid glands secrete ½ of all saliva
      • Saliva is isotonic with plasma
        • Saves osmotic work
      • Saliva is strongly buffered with HCO3- and HPO4-2
      • Secrete continuously, but increased with eating and ruminating
slide9
Mucus glands
    • Include:
      • Palatine glands
      • Buccal glands
      • Pharyngeal glands
    • Properties
      • Vary mucus saliva
      • Isotonic with plasma
      • Saliva is strongly buffered with HCO3- and HPO4-2
      • Low flow when not stimulated
  • Mixed glands
    • Include
      • Submaxillary
      • Sublingual
      • Labial
    • Properties
      • Very mucus saliva
      • Hypotonic to plasma
      • Poorly buffered
      • Variable flow
composition of saliva
Composition of saliva
  • Composition from different glands

HCO3-HPO4-2Cl-Na+K+

Parotid 95 75 13 186 5

Inferior molar 134 48 10 175 9

Palatine and Buccal 109 25 25 179 4

Submaxillary 6 54 6 15 26

  • Composition control
    • Adrenal cortex
      • Aldosterone
    • Kidney
      • Renin
  • Factors affecting saliva composition
    • Sodium deprivation
      • As concentration of Na decreases, the concentration of K increases to maintain concentration of total cations
    • Rate of saliva secretion
      • As rate of secretion increases
        • [Na+] and [HCO3-] increases
        • [K+] and [HPO4-2] decreases
saliva secretion
Saliva secretion
  • Control of secretion
    • Controlled by the vagus nerve through receptors in the mouth, esophagus, reticulum, reticuloruminal fold, and reticulo-omasal orifice
    • Stimuli
      • Stretch up to 20 mm Hg
      • Rumination
slide13
Factors affecting saliva flow
    • Activity of animal

Activity% of saliva flow

Resting 36

Eating 27

Ruminating 37

    • Feed consumption
      • Increased DM intake increases saliva flow
    • Type and physical form of diet
      • Factors that limit rumination will limit saliva flow
      • Saliva secretion will be decreased as:
        • Grain level in the diet increases
        • Maturity of forage in the diet decreases
        • The particle size of the feedstuffs decreases
        • The diet moisture level increases

DietSaliva secretion (gm/gm feed consumed)

Dairy cubes .68

Fresh grass .94

Silage 1.13

Dried grass 3.25

Hay 3.65

saliva s role in buffering the rumen
Saliva’s role in buffering the rumen
  • Significance of the rumen buffering system
    • Enough organic acids are produced in the rumen to cause the pH to drop to 2.8 to 3.0 without buffering
    • Normal rumen pH range is 5.5 to 7.1
  • Components of the rumen buffering system

__pK__Buffering range

HPO4-2 (second H+) 7.1 6-7

HCO3- (first H+) 6.4 5.5-7

Acetate 4.8

Propionate 4.9 5-6

Butyrate 4.8

Lactate 3.9

Glutamate 5.6

Aspartate 5.2 5-6

Alfalfa protein isoelectric point 5.5

NH3 9.3

Cation exchange capacity

role of cation exchange in buffering the rumen
Role of cation exchange in buffering the rumen
  • Cation exchange capacity
    • The concentration of charged groups like proteins, lignins, and pectins that exchange cations like Ca+2, Mg+2, and K+ for H+
    • Cation exchange capacity of different forages

CEC, mEq/100 gm

ForageMechanical pulpNDF

Fescue 59 111

Timothy 68 132

Orchardgrass 72 120

Rice straw 43 57

Alfalfa 152 104

Red clover 169 139

White clover 294 249

buffering range in the rumen
Buffering range in the rumen
  • The rumen is well-buffered for acid, but poorly for alkali
  • Buffer curve

9

8

7

6

5

4

pH

40 20 0 20 40 60 80 100 120

1N KOH added 1N HCl added

ruminant fiber requirement effects of fiber on ruminant intake digestion and metabolism
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

slide18
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 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
slide19
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

slide20
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

slide21

70

40

10

Milk

Milk or body weight

Synthesis, kcal /

100 Kcal ME

above maintenance

  • 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

Body tissue

30 40 50 60 70

Acetic acid, % of total VFA

slide22
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

    • Recent theory

Reduced pH increases production of trans fatty acids from polyunsaturated fatty acids

Trans fatty acids inhibits fatty acid synthesis in the mammary gland

slide23
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 .4

20 .4

16 .36

12 .32

8 .28

4 .24

slide24

40 kg milk

20 kg milk

4

3

2

  • 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

DMI, % BW

Physical limitation

Physiological

control

20 30 40 50

NDF, % DM

slide25
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
slide26
Long-term health problems
    • 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

slide27
Displaced abomasum

Decreased fiber

Muscle atrophy Subclinical acidosis

Decreased feed intake

Empty abomasum

Displaced abomasum

the fiber requirements of ruminant animals
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
        • Minimum of 19% ADF at peak lactation
    • Beef
      • Before 1996 NRC
        • Minimum of 10% roughage
slide29
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

slide30

Feed intake, lb/day

  • Using a static fiber percentage prevents the opportunity to meet the fiber requirement and come close to meeting the energy requirements of high producing dairy cows

Milk production, lb/day

Body weight, lb

0 10 20 30 40

Week of lactation

slide31
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
slide32
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

slide33
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
slide34
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

use of buffers in ruminant diets
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

slide36
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