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
200 liters (50 gallons) in one cow

3. Ruminants Continuous culture fermenters
Input and output
Lignocellulosic substrates digested
Cellulase complex
Hemicellulases
Lysozyme
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 nonruminants

4. 4 Steps of Rumination Regurgitation Remastication Reinsalivation
reverse peristalsis carries food to mouth
Remastication
liquid squeezed from bolus and swallowed
bolus chewed
Reinsalivation
adding more saliva
Redeglution
swallowing bolus and liquid

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 (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
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

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 rumination (extensive)
Decrease particle size for passage
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. Rumen Contractions
Feeding increases frequency and amplitude of contractions
Feeding a finely ground forage reduces number and intensity of contractions
Requires 2-6 weeks to adapt
Metabolic problems
Hardware disease, hypocalcemia, or hyperglycemia will inhibit ruminal contractions

13. Need for Eructation
Peak gas production occurs 30 min to 2 hr post-feeding (12-27 liters/min)
Average is 1-2 liters/min
Approximately 30% of CO2 produced in rumen is absorbed into blood and removed through the lungs
Only 20% of the CH4 is removed through the lungs
Composition of rumen gas
__Gas__ _%__ CO
CH4 (variable) N
O2 (at wall) H
H2S

14. Control of Eructation Stimulus Inhibition
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
Histamine
Inhibition of eructation will cause the animals to bloat
Ruminal pressures will increase to 45 to 100 mm Hg
Stable froth or foam formed in rumen

15. Why Worry about Rumen Microbes?
Microbes make ruminants less efficient!!
Aerobic fermentation:
Anaerobic fermentation:
Glucose + O2 ATP + CO2 + H2O
Glucose acetic acid + propionic acid + butyric acid
+ CO2 + H2O + CH4 + Heat

16. The nutrients presented to the animal after ruminal fermentation
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

17. Rumen Digestion and Fermentation
CO2
VFA
Degradable Rumen Microbial cells
Feed microbes NH3
CH4
Heat
Long-chain
fatty acids
H2S

18. 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

19. 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

20. Symbiotic Relationship
Microbes provide to the ruminant
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

21. Symbiotic Relationship
Microbes provide to the ruminant
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
High biological value protein source
Amino acid pattern is very similar to that required by the ruminant animal

22. Symbiotic Relationship
Microbes provide to the ruminant
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

23. Microbes provide to the ruminant Energy!!!
Symbiotic Relationship
Microbes provide to the ruminant Energy!!!
VFA %
Microbial cells 10%
Digestible unfermented feed 20%
No glucose available for the ruminant
Concentration of VFA
in rumen = 50 to 125 uM/ml

24. Symbiotic Relationship
Microbes provide to the ruminant
Provision of B vitamins
Meets the ruminant’s requirements under most conditions
Some supplementation, such as niacin, may be beneficial in early lactation dairy cows

25. Symbiotic Relationship
Microbes provide to the ruminant
Detoxification of toxic compounds
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 to Australia
Inoculated rumen
Fed Leucaena safely to Australian ruminants!

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

27. Symbiotic Relationship
Ruminants provide to microbes
Housing
Reliable heat (39 ± 2°C)
Fluid environment (free water intake)
85 to 90% water
Guaranteed 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

28. Symbiotic Relationship
Ruminants provide to microbes
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

29. Symbiotic Relationship
Ruminants provide to microbes
Nutrients
Substrates come from feedstuffs that animal consumes
Saliva provides urea (N source for bacteria)

30. Symbiotic Relationship
Ruminants provide to microbes
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 hours/day
Decreases in particle size of forage reduce need for rumination, decrease chewing time, decrease saliva production, and rumen pH plummets

32. Symbiotic Relationship
Ruminants provide to microbes
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

33. Bacteria and pH Tolerance
Species
Type pH
Ruminococcus flavefaciens
Fibrobacter succinogenes
Megasphaera elsdenii
Streptococcus bovis
fiber
lactate user
lactate producer
6.15 6
4.9
4.55

34. Microbes % of mass Generation interval No./mL Bacteria 60-90 20 min
25-80 billion
Protozoa
10-40
8-36 h
thousand
Fungi
5-10
24 h
minimal

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

36. 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

37. 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

38. 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

39. Entodinium (Rumen Protozoa)

40. Rumen Microbes Fungi Known only for about 20 years Numbers usually low
Digest recalcitrant fiber

41. Bacterial Populations
Cellulolytic bacteria (fiber digesters)
digest cellulose
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 from roughage diets

42. Microbial Populations
Amylolytic bacteria (starch, sugar digesters)
digest starch
require pH 5-6
utilize N as NH3 or peptides
produce propionate, butyrate and lactate
predominate from grain diets
rapid change to grain diet causes lactic acidosis (rapidly decreases pH)

43. Microbial Populations
Methane-producing bacteria
produce methane (CH4)
utilized by microbes for energy
represent loss of energy to animal
released by eructation

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

45. 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

46. 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

47. 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

49. Rumen Function Overview