Digestion Index Glossary

Digestive Physiology of Herbivores


Roughly 50% of the organic carbon on earth is tied up in cellulose. This represents an enormous source of energy, yet vertebrate cells do not produce the cellulases necessary to break down this abundant material.

Fortunately, many microbes produce cellulases which allow them to utilize dietary cellulose and other plant wall materials. Cellulolytic microbes inhabit the digestive tract of all animals, allowing the animal to siphon off and assimilate the end products of fermentation, particularly short chain or volatile fatty acids.

The relative value of fermentation to an animal's nutrition pretty much depends on the size of its fermentation vat. Fermentation occurs in the colon of dogs and humans, but their large bowel is rather small and the benefit they gain from fermentation is trivial. In contrast, herbivores make a living on cellulose by possessing massive fermentation vats as part of their digestive tract.

Core concepts in digestive physiology of herbivores are presented as the following topics:

Advanced and supplemental topics related to digestion in herbivores:

Pathophysiology and diseases affecting the digestive system of herbivores:


Last updated on July 13, 2006
Author: R. Bowen
Send comments via form or email to rbowen@colostate.edu