What's a rumen?
Sheep, cattle, goats, deer, giraffes and llamas are ruminant animals. This means that they have a four-chambered stomach. The four chambers of the ruminant stomach are the reticulum, rumen, omasum and abomasum. The rumen serves as a large fermentation vat in which bacteria and other microorganisms reside. These microbes are capable of breaking down feedstuffs that the cow cannot. As part of this process, they produce a number of by-products, such as volatile fatty acids (VFAs), which the animal absorbs and uses as energy. Several gases, including carbon dioxide and methane, are also produced in the fermentation process and must be removed by eructation or belching. The structures present in each chamber of the ruminant stomach are quite unique. The reticulum has a clearly defined honeycomb pattern. The rumen has thousands of papillae to increase surface area. The omasum is full of numerous folds of tissue. Below are a series of videos exploring the ruminant digestive system in several different species.
If you could shrink yourself and take a ride through the gastrointestinal tract of a cow, this is what it would look like. This 3D rendering was put together by the Canadian Museum of Nature and is truly incredible. Hang on for the ride!
Video of a dissection of a sheep gastrointestinal tract.