Ruminants have a stomach with four chambers, which are the Rumen, Reticulum, omasum, and abomasum. In the first two chambers, the rumen and the reticulum, the food is mixed with saliva and separates into layers of solid and liquid material. Solids clump together to form the cud (or bolus). The cud is then regurgitated, chewed slowly to completely mix it with saliva, which further breaks down fibers. Fiber, especially Cellulose, is broken down into Glucose in these chambers by symbiotic bacteria and protozoa. The broken-down fiber, which is now in the liquid part of the contents, then passes through the rumen into the next stomach chamber, the omasum, where water is removed. Then, the digesting food is moved to the last chamber, the abomasum. The food in the abomasum is digested much like it would be in the human stomach. It is finally sent to the small intestine, where the absorption of the nutrients occurs.
It is interesting to note that almost all glucose produced by the breaking down of cellulose is used by the symbiotic bacteria. Ruminants get their energy from the volatile fatty acids produced by these bacteria: Acetic acid, Propionic acid and Butyric acid.