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Rumen
Fermentation
Rumen Fermentation
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World’s largest
commercial
fermentation space
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100 billion liters or
rumen volume in
domestic animals
1010 to 1012 cells/mL
Rumen capacity ranges
from less than 1 liter (1
quart) in a duiker to
200 liters (50 gallons)
in a cow
Ruminants
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Continuous culture fermenters
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Lignocellulosic substrates (forages)
digested
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Input and output
Cellulase complex
Hemicellulases
Nitrogen capture (NPN)
8 x 1015 mouths to feed
Because of these microbial enzymes, ruminants can utilize feedstuffs
that provide little to no nutritional benefit to non-ruminants
Four Steps of Rumination
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Regurgitation
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Remastication
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Liquid squeezed from bolus and
swallowed
Bolus chewed
Reinsalivation
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Reverse peristalsis carries food to mouth
Adding more saliva
Redeglutition
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Swallowing bolus and liquids
Rumination
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Allows animal to forage and eat food rapidly,
and then store for later digestion
Reduces particle size
 Only small particles leave reticulorumen
Increases surface area for microbial
attachment and digestion/fermentation
Breaks down impervious plant walls
Further stimulation of saliva flow (saliva serves
to buffer rumen)
Rumination Time
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Average times for a grazing animal
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Eating – 8 hours
Ruminating – 8 hours
Resting – 8 hours
Ruminating time is quite variable (high
variation)
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Reducing forage:concentrate decreases rumination
Reducing particle size of forage decreases time
spent ruminating
Mechanism of Rumination: Regurgitation
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Stimulus – digesta in fiber mat scratching surface
near cardiac sphincter
Contraction of the reticulum forces digesta to cardia
Animal inhales with epiglottis closed to produce a
vacuum
Cardia sphincter opens and esophagus dilates
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Negative pressure (vacuum) sucks digesta into esophagus
Rapid reverse peristalsis moves digesta to mouth
Mechanism of Rumination: Remastication,
Reinsalivation, and Redeglutition
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Bolus is rechewed
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Chewing is slower and more deliberate than during
initial eating phase
Digesta reinsalivated
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Parotid glands secrete more saliva during rumination
than eating
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Saliva from parotid glands secrete more NaHCO3- than
other glands
Reswallowing
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After reswallowing, the rumen contracts to move
swallowed bolus into the rumen
Remastication
and Redeglutition
Reducing Particle Size of
Ingested Feeds
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Chewing during eating (minimal)
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Chewing during remastication (extensive)
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Preparation for swallowing
Release soluble constituents
Damage plant tissues for microbial attachment
Decrease particle size for passage
Damage plant tissues for microbial attachment
Microbial digestion
Reticuloruminal contractions
Rumen Contractions
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Inoculate incoming feed with microbes
Mix contents
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Minimize effects of stratification
Move fermentation products (VFA’s) to
rumen wall
Particle sorting and passage of small
particles to omasum
Rumination
Eructation of fermentation gases
Need for Eructation
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Peak gas production
occurs 30 min to 2 hr postfeeding (12-27 liters/min)
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Approximately 30% of
CO2 produced in rumen is
absorbed into blood and
removed through the lungs
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Average is 1-2 liters/min
Remainder is eructated
Only 20% of the CH4 is
removed through the lungs
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80% eructated
Composition of rumen
gas
__Gas__
CO2
CH4 (variable)
N2
O2 (at wall)
H2
H2S
_%__
65.35
27.76
7.00
.56
.18
.01
Control of Eructation
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Stimulus
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Gaseous distension of the reticulum and rumen
Esophagus dilates & animal belches
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12-30 L per minute for cattle
3-17 times per minute
Inhibition
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Presence of digesta near the cardiac sphincter
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Affects all three sphincters
Protective mechanism to prevent digesta from entering lungs
Epinephrine – fight or flight response
Inhibition of eructation will cause the animals to bloat
Ruminal pressures will increase up to 100 mm Hg
Stable froth or foam formed in rumen
Feed the Microbes, Let the Microbes Feed the Ruminant!
Feed In
VFA
Microbial Protein
Vitamins
The nutrients presented to the
animal after ruminal fermentation
are very different than those entering
the rumen as feed
Rumen Digestion and Fermentation
Degradable
Feed
Rumen
microbes
CO2
VFA
Microbial cells
NH3
CH4
Heat
Long-chain
fatty acids
H2S
Products in red are used by the host animal
Products listed in black and green are not useable by the animal
Products listed in green are the primary energy losses from the rumen
Location of Microbes
Gas Phase
Rumen
Wall
Fiber Mat
Rumen
Fluid
Rumen Microorganisms
Nutritional Requirements
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CO2
Energy
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Nitrogen
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Ammonia (majority of nitrogen needs)
Amino acids (cellulolytic bacteria)
Minerals
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End products from digestion of structural carbohydrates
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Fermentation of sugars
Co, S, P, Na, K, Ca, Mg, Mn, Fe, Zn, Mo, Se
Vitamins
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None required in mixed cultures of bacteria
Symbiotic Relationship
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Microbes provide to the ruminant
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Digestion of cellulose and hemicellulose
Provision of high quality protein
Production of VFA
Provision of B vitamins
Detoxification of toxic compounds
Digestion of Cellulose and
Hemicellulose
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Cellulases are all of microbial origin
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Without microbes, ruminants would not
be able to use forage crops such as
pasture, hay or silage
Provision of High Quality Protein
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50-80% of absorbed N is from microbes
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Improved microbial efficiency will provide
more microbial protein
Can get over 3 kg of microbial protein per
day in cattle
High biological value protein source
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Amino acid pattern is very similar to that
required by the ruminant animal
Microbes As A Feed Source
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Microbes as a feed source
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Bacteria and protozoa washed out of the
rumen to omasum and into the abomasum
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Acidic environment kills microorganisms
Digested and absorbed the same as any other
feed source in stomach and small intestine
Provide amino acids and some energy
Energy
Sources of energy leaving rumen:
VFA
70%
Microbial cells
10%
Digestible unfermented feed 20%
No glucose available for the ruminant
Concentration of VFA
in rumen = 50 to 125 uM/ml
Provision Of B Vitamins
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Meets the ruminant’s requirements
under most conditions
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Some supplementation of specific vitamins,
such as niacin, may be beneficial in early
lactation dairy cows
Detoxification Of Toxic Compounds
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Many potential toxins are de-toxified by
rumen microbes
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Example:
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Mimosine in Leucaena causes problems
 Poor growth, reproduction and hair loss
Hawaiian ruminants, but not those from Australia,
have microbes that degrade mimosine so Leucaena
could be fed
 Transferred rumen fluid obtaine from Hawaiian
cattle to Australia
 Inoculated rumens of Australian cattle
 Fed Leucaena safely to Australian ruminants!
Symbiotic Relationship
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Ruminants provide to microbes
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Housing
Garbage removal
Nutrients
Optimal environment for growth
Housing
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Reliable heat (39 ± 2°C)
Fluid environment (requires free water
intake)
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85 to 90% water
Guaranteed housing for 18 to 96 hours
depending on diet and type of animal
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Straw-fed water buffalo – longest rumen residence
time for microbes
Small selective browsers (mouse deer or duiker) –
shortest residence time for microbes
Garbage Removal
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Absorption of VFA
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Eructation
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Energy to ruminant
CO2 and CH4
Passage of indigestible residue and
microbes to lower GI tract
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Rumen mixing to separate and settle small
particles
Nutrients
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Substrates come from feedstuffs that
animal consumes
Saliva provides urea (N source for
bacteria)
Optimal Environment For Growth
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Reduced environment (little to no oxygen)
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Strict anaerobic microbes in rumen interior
Functional anaerobes near rumen wall
pH 6.0 to 7.0
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Saliva contains bicarbonate and phosphate buffers
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Cows produce up to 50 gallons of saliva daily
Continuously secreted
More added during eating and rumination
Cow ruminates 10-12 hours/day
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Decreases in particle size of forage reduce need for
rumination, decrease chewing time, decrease saliva
production, and rumen pH plummets
Optimal Environment (pH)
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If pH 5.7 rather than 6.5
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50% less microbial synthesis
Cellulolytic bacteria function best at pH ~6.8
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Amylolytic bacteria function best at pH ~5.8
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Rate of structural carbohydrate use is decreased
More lactate and less acetate is produced
Further downward pH spiral
In concentrate selectors (like deer), parotid
salivary glands are 0.3% of body weight
Symbiotic Relationship
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Microbes provide to the ruminant
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Digestion of cellulose and hemicellulose
Provision of high quality protein
Production of VFA
Provision of B vitamins
Detoxification of toxic compounds
Ruminants provide to microbes
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Housing
Garbage removal
Nutrients
Optimal environment for growth
Microbes
% of mass Generation No./mL
interval
Bacteria
60-90
20 min
25-80
billion
Protozoa
10-40
8-36 h
200-500
thousand
Fungi
5-10
24 h
minimal
Rumen Microbes
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Bacteria
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>200 species with many subspecies
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25 species at concentrations >107/mL
1010 to 1012 cells/mL
99.5% obligate anaerobes
Environmental Niches for Bacteria
 Groups of bacteria in the rumen
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Free-living in the liquid phase
Loosely associated with feed particles
Firmly adhered to feed particles
Associated with rumen epithelium
Attached to surface of protozoa and fungi
Bacteria attached to rice straw
in water buffalo rumen
Benefits of Bacterial Attachment
 Allows bacteria to colonize the digestible surface of
feed particles
 Brings enzymes (from microbes) and substrate (from
feedstuff) together
 Protects microbial enzymes from proteases in the rumen
 If attachment prevented or reduced, digestion of
cellulose greatly reduced
 Retention time of microbes in the rumen is increased to
prolong digestion
 Reduces predatory activity of protozoa
 Over-feeding fat to ruminants can coat forages, reducing
bacterial attachment
Microbial Populations
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Cellulolytic bacteria (fiber digesters)
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Digest cellulose and hemicellulose
Require pH 6-7
Utilize N in form of NH3
Require S for synthesis of sulfur-containing amino
acids (cysteine and methionine)
Produce acetate, propionate, little butyrate,
CO2
Predominate in rumens of cows fed roughage
diets
Microbial Populations
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Amylolytic bacteria
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Digest starches and sugars
Require pH 5-6
Utilize N as NH3 or peptides
Produce propionate, butyrate and lactate
Predominate in rumens of cows fed grain diets
Rapid change to grain diet causes lactic acidosis
(rapidly decreases pH)
Microbial Populations
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Methane-producing bacteria
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Produce methane (CH4)
Utilized by microbes for energy
Represent loss of energy to animal
Released by eructation
Rumen Microbes
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Protozoa
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Large (20-200 microns) unicellular
organisms
Ingest bacteria and feed particles
Engulf feed particles and digest
carbohydrates, proteins and fats
Numbers affected by diet
Entodinium (Rumen Protozoa)
Rumen Microbes
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Fungi
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Existence known for about 25 years
Numbers usually low
Digest recalcitrant fiber
Protozoal organisms
attached to red clover
in rumen of steer 24
hours after feeding
Dietary Factors That Reduce
Microbial Growth
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Rapid, dramatic ration changes
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Takes 3-4 weeks for microbes to stabilize
Restricted amounts of feed
Excessive unsaturated fat
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Bacteria do not use fat for energy
Inhibit fiber digestion and microbial growth
Different types of fat have different effects
Dietary Factors That Reduce
Microbial Growth
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Excessive non-structural carbohydrate
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Lowers rumen pH (rumen acidosis)
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Slug feeding
Feed barley or wheat (rapidly fermented)
To prevent acidosis, must balance lactate users
and producers
Dietary Factors That Maximize
Microbial Growth
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Maximum dry matter intake
Balanced carbohydrate and protein
fractions at the same time
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Bacteria need both energy and N for amino
acid synthesis
Gradual ration changes
Feed available at all times
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Maintains stable rumen pH
Rumen Function Overview