Ammonia constitutes what percent of total non-protein nitrogen (NPN)?

• A. 0.2%
• B. 2%
• C. 20%
• D. 0.02%

Answer: (A)

Non-protein nitrogen is all the nitrogen in feed that isn’t in the form of true proteins. Ammonia is one form of NPN, but in the rumen its free concentration is kept very low relative to the rest of the non-protein nitrogen pool, because it is rapidly used by microbes to make microbial protein. That keeps the share of ammonia among NPN at only about 0.2%. The rest of NPN comes from other compounds such as urea and small amounts of biuret, uric acid, and related substances. So the correct value is 0.2%.