Rumen microbes ferment carbohydrates to volatile fatty acids. Which trio of acids are produced and absorbed to provide most of the ruminant's energy?

• A. Lactic acid, Acetate, Methane
• B. Formate, Propionate, Acetone
• C. Acetate, Propionate, Butyrate
• D. Acetone, Butanol, Ethanol

Answer: (C)

Rumen microbes ferment carbohydrates into volatile fatty acids, and three of these—acetate, propionate, and butyrate—are produced in large amounts and absorbed through the rumen wall to supply most of the animal’s energy. Propionate is especially important because it is the main gluconeogenic substrate, converted in the liver to glucose to keep blood sugar steady. Acetate serves as a major energy source and a building block for fatty acid synthesis, while butyrate provides energy for the rumen lining and can be turned into ketone bodies used by other tissues. Other compounds like lactic acid, formate, acetone, or methane aren’t the primary energy carriers in normal rumen fermentation; methane represents energy lost as gas, and the others don’t account for the majority of energy supply.