Ruminants....

Ruminants: Some Basics

Distinguishing Features

A. Rumination: regurgitation, remastication, re-insalivation, reswallowingB. Eructation: 12-30 L per minute; 3-17 times per minuteC. DigestionD. Fermentation

I. Physical: 4 specialized stomach compartments

70-100 L

5-8 L

3-5 LCollectively, these organs occupy almost 3/4ths of the abdominal cavity, fillingvirtually all of the left side and extending significantly into the right.

The rumen papillaeare key to VFA absorption;health is critical

The honeycomb of the reticulum is well suited forsorting particles by size and for rumination

The folds and plies of theomasum allow ingesta to betrapped and squeezed to allow dehydration prior todelivery to the abomasum

Rumen OmasumReticulum

Ruminants: Some Basics

Distinguishing Features

A. Rumination: regurgitation, remastication, re-insalivation, reswallowingB. Eructation: 12-30 L per minute; 3-17 times per minuteC. DigestionD. Fermentation

I. Physical: 4 specialized stomach compartments

Ruminants: Some Basics

Distinguishing Features

A. Cellulase complexB. HemicellulasesC. LysozymeD. Nitrogen Capture (NPN)

II. Chemical: specialized enzymes and processes

Because of these enzymes and abilities, ruminants can utilize feedstuffs that provide little to no nutritional benefit to nonruminants.

Ruminants: Some Basics

Distinguishing Features

A. Fiber digestionB. Starch digestionC. Urea utilization

III. Microbial: specialized microbial population; bacteria, protozoa, fungi

Feed InVFAMicrobial ProteinVitamins

The nutrients presented to thecow or steer by the rumen arevery different than those enteringthe rumen as feed.

Rumen Function and Development

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

I. Organization, function, and special relationshipsamong compartments

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

d. it is the VFAs that provide the bulk of theenergy 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

Some Basics

Digestion

Fermentation

All CHO must passthrough Pyruvate tobecome VFA

Some Basics

Nonstructural polysaccharidesStructural polysaccharides

VFA, H+

Pyruvate Lactate

Rumen pH must be defended in the face oforganic acids and H+ production to preventacidosis.

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

Some Basics

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 epitheliumperforms at least 3 majorfunctions:

• protection• metabolism• absorption

VFA are absorbed passively; thus,the concentration gradient from lumento blood supply must be maintained. Metabolism of some VFA within thecells of the papillae help ensure agradient.

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

Some Basics