What is the function of the rumen microbiome in digestion?

• A. Absorbs nutrients in the small intestine
• B. Ferments fibrous feeds to produce volatile fatty acids and synthesize microbial protein
• C. Produces bile for fat digestion
• D. Stores rumen gas for later use

Answer: (B)

The main function of the rumen microbiome is to break down fibrous plant material through fermentation, producing two crucial digestive products: volatile fatty acids and microbial protein. A diverse community of microbes in the rumen treats cellulose and other fibers that the animal can’t digest on its own, enabling the breakdown of plant cell walls. The volatile fatty acids produced—acetic, propionic, and butyric acids—are absorbed through the rumen wall and become the primary energy source for the animal. Meanwhile, the microbes themselves grow and multiply, and their protein becomes a significant source of amino acids for the animal when the digested microbial biomass moves to the lower gut. Other options don’t fit because bile is made by the liver for fat digestion, and rumen gas is produced and expelled rather than stored, while absorption of nutrients mostly occurs in the small intestine rather than directly in the rumen.