Which nutrient is not produced by rumen microbes?

• A. Volatile fatty acids
• B. Amino acids
• C. B vitamins
• D. Vitamin C

Answer: (D)

Rumen microbes ferment fibrous feed to make the animal’s main energy supply in the form of volatile fatty acids, and their own biomass provides amino acids as microbial protein for the host. They also synthesize B vitamins that the animal can use. Vitamin C, however, is not produced by rumen microbes in the fermentation process; ruminants either synthesize it in tissues or obtain it from the diet, but the rumen fermentation itself isn’t a source of Vitamin C.