KEY POINTS

1. Fermentation is the metabolic action of bacteria.

2. The sites of fermentative digestion must be conducive to microbial growth.

Microbial Ecosystem of Fermentative Digestion

1.

2. Cooperation and interplay among the many species of microbes give rise to a complex ecosystem in the forestomach and hindgut.

Substrates and Products of Fermentative Digestion

1. Plant cell walls are important substrates for fermentative digestion and significant nutrient sources for many species.

2. Nutrients other than cell walls are also subject to fermentative digestion.

3. Anaerobic conditions in the rumen result in metabolic activities leading to the production of volatile fatty acids.

4. Volatile fatty acids are important energy substrates for the host animal.

5. Fermentative digestion of protein results in the deamination of a large portion of amino acids.

6. When protein and energy availability in the forestomach are well matched, rapid microbial growth and efficient protein utilization result.

7. Microbial protein can be synthesized in the rumen from nonprotein nitrogen sources.

Reticulorumen Motility and Maintenance of the Rumen Environment

1. The physiological functions of the reticulorumen maintain an environment favorable to fermentation patterns that are beneficial to the host.

2. Rumen fermentation is maintained by selectively retaining actively fermenting material while allowing Unfermentable residue to pass on to the abomasum.

3. Gravity and reticulorumen motility combine to create the selective flow of particulate matter out of the rumen.

4. Functional specific gravity determines the rate at which particulate matter (solids) moves through the zones of the reticulorumen.

5. Digestibility and physical characteristics of feed have important influences on both the rate of particle passage from the rumen and the rate of feed intake.

6. Rumination, or cud chewing, has an important effect on the reduction of particle size and the movement of solid material through the rumen.

7. Water moves through the rumen at a much faster rate than particulate matter.

8. Rumen dilution rate has important influences on fermentation and microbial cell yield.

Control of Reticulorumen Motility

1. Reticulorumen motility is controlled by the central nervous system and affected by intraluminal conditions.

Omasal Function

1. Passage of material from the reticulum to the omasum occurs during reticular contraction.

Volatile Fatty-Acid Absorption

1. Volatile fatty acids, representing 60% to 80% of the energy needs of the animal, are absorbed directly from the forestomach epithelium.

Rumen Development and Esophageal Groove Function

1. Significant changes in forestomach size and function occur with dietary changes in early life.

2. The esophageal groove diverts the flow of ingested milk past the forestomach and into the abomasum.

Function of the Equine Large Hindgut

1. The equine hindgut has a great capacity for fermentation.

2. The types of substrate and fermentation patterns are essentially identical for forestomach and hindgut fermentation.

3. The motility functions of the cecum and colon retain material for fermentation and separate particles by size.

4. The rate of fermentation and volatile fatty-acid production in the equine colon is similar to that in the rumen.

5. Hindgut anatomy and function vary greatly among the many species of veterinary interest.