Key Concept: In ruminants, rumen microbes break down most dietary protein into ammonia before it ever reaches the intestine.
Why it's correct: Bypass protein (UIP) is the fraction that escapes this rumen breakdown and passes intact to the small intestine, where it is digested and absorbed directly — valuable for high-yield animals needing extra quality protein.
Why others fail: It isn't protein that's fully degraded in the rumen (that's the opposite fraction), doesn't bypass digestion entirely (it IS digested, just later), and has nothing to do with nitrogen content.