(5) Fermentation & VFAs

Microbial digestion

Digestion performed by microorganisms through fermentation.

Microorganisms involved in fermentation

Bacteria, yeast, fungi, and protozoa.

Fermentation

Breakdown of complex carbohydrates by microorganisms.

Complex carbohydrates

Fiber, including cellulose, hemicellulose, and pectin.

Major fermentation end-products

VFAs, gas, and vitamins.

VFA

Volatile fatty acid; a short-chain fatty acid produced by microbial fermentation.

Ruminant primary fermentation vat

Rumen.

Hindgut fermenter primary fermentation vat

Large intestine.

Monogastric primary fermentation vat

Large intestine.

Ruminant fermentation location

Foregut and hindgut.

Hindgut fermenter fermentation location

Hindgut, primarily the large intestine.

Monogastric fermentation location

Hindgut, primarily the large intestine.

Ruminant rumen size

About 60% of the GIT.

Hindgut fermenter large intestine size

About 62% of the GIT.

Monogastric large intestine size

About 20% of the GIT.

Ruminant energy from VFAs

More than 70% of energy needs.

Hindgut fermenter energy from VFAs

About 55-65% of energy needs.

Monogastric energy from VFAs

About 30% of energy needs.

Butyrate

Primarily used by rumen or intestinal papillae for growth.

Acetate

Mainly oxidized by tissues to produce ATP or used as a precursor for fat synthesis.

Propionate

Used by the liver for gluconeogenesis and is critical for glucose production.

Microbial protein

Protein from microbial bodies that pass through the GIT and can be absorbed as a source of nitrogen.

Why ruminants benefit from microbial protein

Microbial bodies pass from the rumen into later sections of the GIT where they can be absorbed as a high-quality nitrogen source.

Why hindgut fermentation is less efficient for nutrient recovery

Microbial bodies are produced near the end of the GIT and are largely eliminated as feces.

Coprophagy

Eating feces to recover nutrients from hindgut fermentation.