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How do symbiotic microorganisms help herbivores digest cellulose?

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Diagram of the human digestive system viewed from the front, showing and labeling organs including the mouth, teeth, tongue, salivary glands, pharynx, esophagus, liver, stomach, gallbladder, pancreas, large intestine, small intestine, appendix, rectum, and anus. — digestion The human digestive system as seen from the front.

Most animals lack the necessary enzymes, such as cellulase, to break down cellulose, a primary component of plant cell walls. To overcome this, many herbivores have evolved a symbiotic relationship with microorganisms that reside within their digestive tracts.123

These microorganisms assist in digestion through a process called fermentation. In ruminant species, this occurs in a specialized stomach chamber known as the rumen, while other herbivores, known as hindgut fermenters, utilize a cecum located at the end of the small intestine.1

During fermentation, the symbiotic bacteria break down cellulose into acetic acid and other short-chain [fatty acids]. These products are then absorbed by the host animal and utilized as essential energy sources. Additionally, these microorganisms can degrade proteins and synthesize certain vitamins, further contributing to the host's nutritional needs.13