What is the purpose of non-protein nitrogen (NPN) in ruminant diets?

• A. To provide nitrogen that can be converted to protein by rumen microbes.
• B. To directly supply amino acids to the animal.
• C. To increase energy density of the diet.
• D. To supply minerals for bone development.

Answer: (A)

Non-protein nitrogen serves as a nitrogen source for the microbes in the rumen. These microbes are the factory that makes microbial protein, which is then passed to the animal and digested to provide amino acids. When there is enough fermentable energy (from carbohydrates) for the microbes to grow, they take that nitrogen and convert it into microbial protein. The animal benefits from this microbial protein, not from amino acids delivered directly or from any direct energy increase. NPN isn’t used to supply minerals or raise the diet’s energy density. It must be used with proper energy supply to avoid ammonia buildup and potential toxicity.