Cellulose is an insoluble dietary fiber, indigestible for humans but not for cows and other large ruminant herbivores.
In reality, no mammal is able to produce enzymes capable of degrading cellulose .
The digestion of this fiber is then entrusted to the symbiosis with so-called cellulolytic bacteria (eg Ruminococci ), housed in the stomach (rumen) of the animal.
These microbes transform cellulose into glucose, which is immediately fermented into short-chain fatty acids. These fatty acids are absorbed by the animal's intestine and used as an energy source.
