Ruminants....

Ruminants: Some Basics Distinguishing Features I. Physical: 4 specialized stomach compartments A. Rumination: regurgitation, remastication, re-insalivation, reswallowing B. Eructation: 12-30 L per minute; 3-17 times per minute C. Digestion D. Fermentation

70-100 L Collectively, these organs occupy almost 3/4ths of the abdominal cavity, filling virtually all of the left side and extending significantly into the right. 3-5 L 5-8 L

Rumen Reticulum Omasum The honeycomb of the reticulum is well suited for sorting particles by size and for rumination The folds and plies of the omasum allow ingesta to be trapped and squeezed to allow dehydration prior to delivery to the abomasum The rumen papillae are key to VFA absorption; health is critical Rumen Reticulum Omasum

Ruminants: Some Basics Distinguishing Features I. Physical: 4 specialized stomach compartments A. Rumination: regurgitation, remastication, re-insalivation, reswallowing B. Eructation: 12-30 L per minute; 3-17 times per minute C. Digestion D. Fermentation

Ruminants: Some Basics Distinguishing Features II. Chemical: specialized enzymes and processes A. Cellulase complex B. Hemicellulases C. Lysozyme D. Nitrogen Capture (NPN) Because of these enzymes and abilities, ruminants can utilize feedstuffs that provide little to no nutritional benefit to nonruminants.

Ruminants: Some Basics Distinguishing Features III. Microbial: specialized microbial population; bacteria, protozoa, fungi A. Fiber digestion B. Starch digestion C. Urea utilization

The nutrients presented to the cow or steer by the rumen are Feed In VFA Microbial Protein Vitamins The nutrients presented to the cow or steer by the rumen are very different than those entering the rumen as feed.

Rumen Function and Development Organization, function, and special relationships among compartments I. A. The 4 compartments or four chambers: 1. Rumen: digestion and fermentation vat (VFA production) 2. Reticulum: mixing aid (feed, water, saliva) 3. Omasum: Dehydration by compression/squeezing removes 60-70% of water from ingesta 4. Abomasum: “true stomach”; acid secretion, lysozyme

Rumen Function and Development 1. Rumen: digestion and fermentation vat a. conditions must be maintained to support microbial growth 1. temperature, moisture, pH buffered 2. constant supply of nutrients 3. continuous removal of products of digestion/fermentation (gases, VFA, ammonia)

Rumen Function and Development b. products of fermentation provide bulk of energy to animal 1. Starch and cellulose digestion 2. Anaerobic metabolism (fermentation) 3. Volatile fatty acid (VFA) production

Rumen Function and Development c. complex polysaccharides are digested to yield sugars that are fermented to produce VFA 1. Structural polysaccharides: cellulose, hemicellulose digested by cellulases and hemicellulases 2. Cellulase is not a single enzyme, but a complex (affinity factor + hydrolytic factor) 3. Protozoa engulf starch particles to digest them 4. Microbes attach to (colonize) fiber components and secrete enzymes

Acetate, Butyrate, Propionate Some Basics d. it is the VFAs that provide the bulk of the energy to the ruminant 1. Bacterial sugar metabolism differs from that of aerobic organisms. 2. VFA are produced from pyruvate by fermentation Polysaccharides Galactose Sucrose Fructose Maltose Glucose Acetate, Butyrate, Propionate

Digestion Fermentation All CHO must pass through Pyruvate to become VFA

Some Basics Pyruvate Lactate VFA, H+ Nonstructural polysaccharides Structural polysaccharides Pyruvate Lactate VFA, H+ Rumen pH must be defended in the face of organic acids and H+ production to prevent acidosis.

Some Basics e. rumen pH must be defended 1. VFAs (acids) produced must be removed 2. Passively absorbed across rumen wall 3. Helps maintain pH at 6.7  .5 4. Saliva also provides buffering capacity cattle: 180 L per day (70% water entering rumen) 5. Saliva is rich in Na, K, PO4, HCO3

Rumen papillae epithelium performs at least 3 major functions: protection metabolism absorption VFA are absorbed passively; thus, the concentration gradient from lumen to blood supply must be maintained. Metabolism of some VFA within the cells of the papillae help ensure a gradient.

Some Basics II. Rumen Development A. Newborns are not functional ruminants 1. Lack sucrase 2. Limited amylase 3. Lactase: galactose, glucose 4. Ability to digest non-starch polysaccharides precedes that for starch

Some Basics B. Rumen Development Begins Early 1. Depends on: a. fibrous diet b. inoculation c. VFA stimulation

Some Basics C. Inoculation occurs by: 1. Feed 2. Inter-animal contact (saliva) 3. Manure, soil *occurs with isolation, but much slower and less completely