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 feed Because of these microbial enzymes, ruminants can utilize feedstuffs that provide little to no nutritional benefit to nonruminants

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

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 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 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

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

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

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

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

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!!! Symbiotic Relationship 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 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 pH Ruminococcus flavefaciens Fibrobacter succinogenes Megasphaera elsdenii Streptococcus bovis fiber lactate user lactate producer 6.15 6 4.9 4.55

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

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

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

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 Gas Phase Fiber Mat Rumen Wall Rumen Fluid

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