Saliva and the Fiber Requirements of Ruminants

1
Saliva and the Fiber Requirements of Ruminants

• Nutrient Requirements of Beef CattleSeventh
  Revised EditionUpdate 2000. pp. 129-130.
  Available at http//search.nap.edu/books/0309069
  343/html/
• Nutrient Requirements of Dairy CattleSeventh
  Revised Edition, 2001. Chapter 4, pp. 34-42.
  Available at httpsearch.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. 801463-1481.
• Available at http//jds.fass.org/cgi/reprint/80/7
  /1463.pdf

2
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

3

• 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
• 
  SalivaMcDougalls solution
• 
  01000 250750 500500 01000
• DMI, BW 1.23
  3.5 5.1 1.23
• Reticular contractions, 1.4
  5.7

4
Salivas role in recycling N and minerals

• Nitrogen
• In a 24 hour period, a 700 kg cow receiving a
  mixed haygrain 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
5

• 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

6

• 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)
• CP N recycled (saliva) N
  recycled (Gut wall)
• g/d of
  total g/d of total

7

• 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

8
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

9

• 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

10
The salivary glands
11
Composition of saliva

• Composition from different glands
• HCO3-
  HPO4-2 Cl- 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

12
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

13

• 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
• Diet Saliva secretion
  (gm/gm feed consumed)
• Dairy cubes
  .68
• Fresh grass
  .94
• Silage
  1.13

14
Salivas 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

15
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 Ca2, Mg2, and K for H
• Cation exchange capacity of different forages
• 
  CEC, mEq/100 gm
• Forage
  Mechanical pulp NDF
• Fescue
  59 111
• Timothy
  68 132
• Orchardgrass
  72 120
• Rice straw
  43 57
• Alfalfa
  152 104
• Red clover
  169 139
• White clover
  294 249

16
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
17
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 gt 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
• eNDF pH 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

18

• 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

19

• 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
20

• 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
• 
  HayConcentrate
• 6040
  4060 2080
• 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

21

• 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
• 
  Haygrain ratio
• Item
  6040 4060 2080
• 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

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
22

• 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

23

• 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
  .4
• 20
  .4
• 16
  .36

24

• 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
25

• 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
• Fibers role on low fiber diets
• Saliva flow
• Provides buffers
• Prevents undesirable microorganisms
• Dilutes VFAs
• Increases liquid turnover
• Motility

26

• 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

27

• Displaced abomasum
• 
  Decreased fiber
• Muscle atrophy
  Subclinical acidosis
• 
  Decreased feed intake
• 
  Empty abomasum
• 
  Displaced abomasum

28
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

29

• 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
• NDF ADF CF
• 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
• NDF ADF CF
• r
• Feed volume .78 .62 .71
• NDF is more highly related to chewing time than
  CF or ADF
• NDF ADF CF
• r
• Chewing time .86 .73 .76

30

• 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

Feed intake, lb/day
Milk production, lb/day
Body weight, lb
0 10 20
30 40
Week of lactation
31

• 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
  lt 35 DM

32

• 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

33

• 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
  Diet
• Minimum 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

34

• Additional recommendations for dairy cattle
• 
  of diet DM
• Nonstructural carbohydrates
  30-40
• Non-fiber carbohydrates
  32-42
• Mertens 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

35
Use of buffers in ruminant diets

• Functions of buffers
• Increase ruminal pH
• Maintain DM intake
• Prevent acidosis
• Increase liquid turnover
• Buffers commonly used
• Buffer Additional
  effects Preventative 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

36

• 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 lt Protein
• Milk fat is lt 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 dont cure all problems associated with
  low fiber diets