What is the rumen?

• A. Kidney
• B. Liver
• C. Small intestine
• D. Large fermentation chamber

Answer: (D)

The rumen is where fiber from plant material is broken down by a huge community of microbes in an anaerobic environment. It’s the largest compartment of the ruminant stomach and acts as a big fermentation chamber, allowing microbes to ferment cellulose and other carbohydrates into volatile fatty acids that the animal uses for energy. The rumen also mixes and stores ingested feed, supports cud chewing and regurgitation to continue the fermentation process, and has papillae to increase surface area for absorbing the fermentation end products. The other organs listed have different roles (kidneys filter waste, liver processes nutrients, the small intestine absorbs nutrients after digestion) and don’t serve the fermentation function the rumen does.