Glossary
Caecal fermentation.
Direct answer
Caecal fermentation is the microbial breakdown of plant fibre in the caecum, a large blind-ended pouch at the start of the large intestine. Bacteria, archaea and fungi break down cellulose and other fibres that the host's own enzymes cannot attack, releasing mainly short-chain fatty acids and gases as products.
Fermenting is not the same as digesting with the host's own enzymes: the host supplies space, warmth and moisture, while micro-organisms do the work. Their composition adjusts to the usual ration, so an abrupt change of feed unsettles the balance of this ecosystem long before anything becomes visible from the outside.
In the horse, the caecum is a fermentation vessel of considerable size and forms the core of fibre utilisation. In humans the caecum is small, fermentation takes place mainly in the colon and contributes far less to the energy supply. Any comparison between the two species has to keep this structural difference in view.
Short-chain fatty acidsGut microbiotaMetagenomicsBioavailability
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