Rumen Fermentation

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

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

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

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)

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

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

Remastication and Redeglutition

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

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

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

Remainder is eructated Only 20% of the CH4 is

removed through the lungs

80% eructated

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 – 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 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

VFADegradable Rumen Microbial cells Feed microbes NH3

CH4

Heat Long-chain fatty acids H2SProducts in red are used by the host animal

Products listed in black and green are not useable by the animalProducts listed in green are the primary energy losses from the rumen

Location of Microbes

Rumen Wall

Rumen Fluid

Fiber Mat

Gas Phase

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 of bacteria

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

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

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

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

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

Energy

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

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!

Symbiotic Relationship Ruminants provide to microbes

Housing Garbage removal Nutrients Optimal environment for growth

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

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

Nutrients Substrates come from feedstuffs

that animal consumes Saliva provides urea (N source for

bacteria)

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

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

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

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

Bacteria attached to rice straw in water buffalo rumen

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

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

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)

Microbial Populations Methane-producing bacteria

Produce methane (CH4) Utilized by microbes for energy Represent loss of energy to animal Released by eructation

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

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

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