The rumen is the largest compartment of a ruminant's stomach, which includes animals like cows, sheep, and goats. It plays a crucial role in the digestion of fibrous plant material. The rumen contains billions of microorganisms that help break down complex carbohydrates, allowing the animal to extract nutrients from tough plant fibers. In addition to aiding digestion, the rumen also serves as a fermentation chamber. This process produces volatile fatty acids, which are a primary energy source for ruminants. The rumen's unique structure and function enable these animals to thrive on a diet primarily composed of grass and other roughage.