1. Rumen
Fermentation

2. Rumen Fermentation
 World’s largest
commercial
fermentation space
 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

3. Ruminants
 Continuous culture fermenters
 Input and output
 Lignocellulosic substrates (forages)
digested
 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

4. Four Steps of Rumination
 Regurgitation
 Reverse peristalsis carries food to mouth
 Remastication
 Liquid squeezed from bolus and
swallowed
 Bolus chewed
 Reinsalivation
 Adding more saliva
 Redeglutition
 Swallowing bolus and liquids

5. Rumination
 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)

6. Rumination Time
 Average times for a grazing animal
 Eating – 8 hours
 Ruminating – 8 hours
 Resting – 8 hours
 Ruminating time is quite variable (high
variation)
 Reducing forage:concentrate decreases rumination
 Reducing particle size of forage decreases time
spent ruminating

7. Mechanism of Rumination: Regurgitation
 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
 Negative pressure (vacuum) sucks digesta into esophagus
 Rapid reverse peristalsis moves digesta to mouth

8. Mechanism of Rumination: Remastication,
Reinsalivation, and Redeglutition
 Bolus is rechewed
 Chewing is slower and more deliberate than during
initial eating phase
 Digesta reinsalivated
 Parotid glands secrete more saliva during rumination
than eating
 Saliva from parotid glands secrete more NaHCO3- than
other glands
 Reswallowing
 After reswallowing, the rumen contracts to move
swallowed bolus into the rumen

9. Remastication
and Redeglutition

10. Reducing Particle Size of
Ingested Feeds
 Chewing during eating (minimal)
 Preparation for swallowing
 Release soluble constituents
 Damage plant tissues for microbial attachment
 Chewing during remastication (extensive)
 Decrease particle size for passage
 Damage plant tissues for microbial attachment
 Microbial digestion
 Reticuloruminal contractions

11. Rumen Contractions
 Inoculate incoming feed with microbes
 Mix contents
 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

12. Need for Eructation
 Peak gas production Composition of rumen
occurs 30 min to 2 hr post- gas
feeding (12-27 liters/min)
 Average is 1-2 liters/min
 Approximately 30% of CO2 __Gas__ _%__
produced in rumen is CO2 65.35
absorbed into blood and CH4 (variable) 27.76
removed through the lungs N2 7.00
 Remainder is eructated
O2 (at wall) .56
 Only 20% of the CH4 is
removed through the lungs H2 .18
 80% eructated H2S .01

13. Control of Eructation
 Stimulus
 Gaseous distension of the reticulum and rumen
 Esophagus dilates & animal belches
 12-30 L per minute for cattle
 3-17 times per minute
 Inhibition
 Presence of digesta near the cardiac sphincter
 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

14. 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

15. Rumen Digestion and Fermentation
CO2
VFA
Degradable Rumen Microbial cells
Feed microbes 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

16. Location of Microbes
Gas Phase
Rumen Fiber Mat
Wall
Rumen
Fluid

17. Rumen Microorganisms
Nutritional Requirements
 CO2
 Energy
 End products from digestion of structural carbohydrates

Fermentation of sugars
 Nitrogen
 Ammonia (majority of nitrogen needs)
 Amino acids (cellulolytic bacteria)
 Minerals
 Co, S, P, Na, K, Ca, Mg, Mn, Fe, Zn, Mo, Se
 Vitamins
 None required in mixed cultures of bacteria

18. Symbiotic Relationship
 Microbes provide to the ruminant
 Digestion of cellulose and hemicellulose
 Provision of high quality protein
 Production of VFA
 Provision of B vitamins
 Detoxification of toxic compounds

19. Digestion of Cellulose and
Hemicellulose
 Cellulases are all of microbial origin
 Without microbes, ruminants would not be
able to use forage crops such as pasture,
hay or silage

20. Provision of High Quality Protein
 50-80% of absorbed N is from microbes
 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
 Amino acid pattern is very similar to that
required by the ruminant animal

21. Microbes As A Feed Source
 Microbes as a feed source
 Bacteria and protozoa washed out of the
rumen to omasum and into the abomasum
 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

22. 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

23. Provision Of B Vitamins
 Meets the ruminant’s requirements
under most conditions
 Some supplementation of specific vitamins,
such as niacin, may be beneficial in early
lactation dairy cows

24. Detoxification Of Toxic Compounds
 Many potential toxins are de-toxified by
rumen microbes
 Example:
 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!

25. Symbiotic Relationship
 Ruminants provide to microbes
 Housing
 Garbage removal
 Nutrients
 Optimal environment for growth

26. Housing
 Reliable heat (39 ± 2°C)
 Fluid environment (requires free water intake)
 85 to 90% water
 Guaranteed housing for 18 to 96 hours
depending on diet and type of animal
 Straw-fed water buffalo – longest rumen residence
time for microbes
 Small selective browsers (mouse deer or duiker) –
shortest residence time for microbes

27. Garbage Removal
 Absorption of VFA
 Energy to ruminant
 Eructation
 CO2 and CH4
 Passage of indigestible residue and
microbes to lower GI tract
 Rumen mixing to separate and settle small
particles

28. Nutrients
 Substrates come from feedstuffs that
animal consumes
 Saliva provides urea (N source for
bacteria)

29. Optimal Environment For Growth
 Reduced environment (little to no oxygen)
 Strict anaerobic microbes in rumen interior
 Functional anaerobes near rumen wall
 pH 6.0 to 7.0
 Saliva contains bicarbonate and phosphate
buffers

Cows produce up to 50 gallons of saliva daily

Continuously secreted

More added during eating and rumination

Cow ruminates 10-12 hours/day
 Decreases in particle size of forage reduce need for
rumination, decrease chewing time, decrease saliva
production, and rumen pH plummets

31. Optimal Environment (pH)
 If pH 5.7 rather than 6.5
 50% less microbial synthesis
 Cellulolytic bacteria function best at pH ~6.8
 Rate of structural carbohydrate use is decreased
 Amylolytic bacteria function best at pH ~5.8

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

32. Symbiotic Relationship
 Microbes provide to the ruminant
 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
 Housing
 Garbage removal
 Nutrients
 Optimal environment for growth

33. 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

34. Rumen Microbes
 Bacteria
 >200 species with many subspecies
 25 species at concentrations >107/mL
 1010 to 1012 cells/mL
 99.5% obligate anaerobes

35. Environmental Niches for Bacteria
 Groups of bacteria in the rumen
 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

36. 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

37. Microbial Populations
 Cellulolytic bacteria (fiber digesters)
 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

38. Microbial Populations
 Amylolytic bacteria
 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)

39. Microbial Populations
 Methane-producing bacteria
 Produce methane (CH4)
 Utilized by microbes for energy
 Represent loss of energy to animal
 Released by eructation

40. Rumen Microbes
 Protozoa
 Large (20-200 microns) unicellular
organisms
 Ingest bacteria and feed particles
 Engulf feed particles and digest
carbohydrates, proteins and fats
 Numbers affected by diet

41. Entodinium (Rumen Protozoa)

42. Rumen Microbes
 Fungi
 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

43. Dietary Factors That Reduce
Microbial Growth
 Rapid, dramatic ration changes
 Takes 3-4 weeks for microbes to stabilize
 Restricted amounts of feed
 Excessive unsaturated fat
 Bacteria do not use fat for energy
 Inhibit fiber digestion and microbial growth
 Different types of fat have different effects

44. Dietary Factors That Reduce
Microbial Growth
 Excessive non-structural carbohydrate
 Lowers rumen pH (rumen acidosis)
 Slug feeding
 Feed barley or wheat (rapidly fermented)

To prevent acidosis, must balance lactate users
and producers

45. Dietary Factors That Maximize
Microbial Growth
 Maximum dry matter intake
 Balanced carbohydrate and protein
fractions at the same time
 Bacteria need both energy and N for amino
acid synthesis
 Gradual ration changes
 Feed available at all times
 Maintains stable rumen pH

47. Rumen Function Overview