Final answer:
Non-protein N sources like urea are rapidly converted to ammonia in the rumen. This step is a part of the urea cycle, helping detoxify ammonia and allowing its use by rumen microbes for protein synthesis.
Step-by-step explanation:
Non-protein N sources, like urea, are rapidly converted to ammonia in the rumen. This conversion is part of the urea cycle, a crucial process in many animals to detoxify ammonia, which is toxic. In ruminants such as cows, the rumen hosts microorganisms that break down urea into ammonia, which can then be used by these microbes to produce amino acids and proteins that the host animal can utilize.
The process of breaking down proteins into amino acids and then deaminating these acids results in the formation of ammonia. Due to the toxicity of ammonia, mammals have evolved the urea cycle in the liver where ammonia is converted into urea, which is less toxic and can be excreted more safely.
However, in the case of non-protein nitrogen sources such as urea being ingested by ruminants, this urea is not directly excreted but first transformed back into ammonia within the rumen, to be used by rumen microflora.