== Explanation ==[[File:Ruversin.jpg|thumb|350px|right|Food digestion in the simple stomach of non-ruminant animals versus ruminantsref]]
The primary difference between a ruminant and non-ruminant (called [[monogastric]]s, such as humans, dogs, and pigs) is that ruminants have a four-compartment stomach. The four parts of the stomach are the [[rumen]], [[Reticulum (anatomy)|]], [[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 .
The cud is then regurgitated and chewed to completely mix it with saliva and to break down the particle size. Fiber, especially [[cellulose]] and [[hemi-cellulose]], is primarily broken down in these chambers by microbes (mostly [[bacteria]], as well as some [[protozoa]], [[fungi]] and [[yeast]]) into the three [[volatile fatty acids]] (VFAs), [[acetic acid]], [[propanoic acid|proprionic acid]] and butyric acid. Protein and non-structural carbohydrate ([[pectin]], [[sugars]], [[starches]]) are also fermented.