Rumen Fermentation

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

Ruminants Continuous culture fermenters

Input and output Lignocellulosic substrates digested

Cellulase complex Hemicellulases Lysozyme Nitrogen capture (NPN)

8 x 1015 mouths to feedBecause of these microbial enzymes, ruminants can utilize feedstuffs that provide little to no nutritional benefit to nonruminants

4 Steps of Rumination Regurgitation

reverse peristalsis carries food to mouth

Remastication liquid squeezed from bolus and

swallowed bolus chewed

Reinsalivation adding more saliva

Redeglution swallowing bolus and liquid

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)

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

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

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

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 Damage plant tissues for microbial attachment

Microbial digestion Reticuloruminal contractions

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

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

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__ _%__ CO2 65.35 CH4 (variable) 27.76 N2 7.00 O2 (at wall) .56 H2 .18 H2S .01

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 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

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

Feed InVFAMicrobial ProteinVitamins

The nutrients presented to the animal after ruminal fermentationare very different than those enteringthe rumen as feed

Feed the Microbes, Let the Microbes Feed the Ruminant!

Rumen Digestion and Fermentation

CO2 VFA

Degradable Rumen Microbial cells Feed microbes NH3

CH4 Heat Long-chain fatty acids H2S

Rumen MicroorganismsNutritional 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

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

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

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

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

Microbes provide to the ruminant Energy!!!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

Symbiotic Relationship

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

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!

Symbiotic Relationship Ruminants provide to microbes

Housing Garbage removal Nutrients Optimal environment for growth

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

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

Symbiotic Relationship Ruminants provide to microbes

Nutrients Substrates come from feedstuffs that

animal consumes Saliva provides urea (N source for

bacteria)

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 10-12 hours/day Decreases in particle size of forage reduce

need for rumination, decrease chewing time, decrease saliva production, and rumen pH plummets

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

Bacteria and pH Tolerance

Species Type pHRuminococcus flavefaciensFibrobacter succinogenesMegasphaera elsdeniiStreptococcus bovis

fiberfiber

lactate userlactate

producer

6.156

4.94.55

Microbes% of mass

Generation interval

No./mL

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 Bacteria

>200 species with many subspecies 25 species at concentrations >107/mL

1010 to 1012 cells/mL 99.5% obligate anaerobes

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

Environmental Niches for Bacteria

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

Benefits of Bacterial Attachment

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

Entodinium (Rumen Protozoa)

Rumen Microbes Fungi

Known only for about 20 years Numbers usually low Digest recalcitrant fiber

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

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)

Microbial Populations Methane-producing bacteria

produce methane (CH4) utilized by microbes for energy represent loss of energy to animal released by eructation

Location of Microbes

Rumen Wall

Rumen Fluid

Fiber Mat

Gas Phase

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

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

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

Rumen Function Overview