Dear Lawrence,

How are you doing?  Busy with your project?

This is a typical question for a ruminant nutritionist. Please send an email to [email protected]

Best regards,

Marinus

Proteins consist of long chains of subunits called amino acids.. Protein metabolism has two parts formation and destruction of proteins for energy production, Formation of proteins is associated with use of amino acids to form main chain. Destruction leads to protein catabolism and form simple amino acids, its needs further digestion and simplification to generate inorganic nitrogenous compound.  But there is a possibility that in oil seed cake catabolism colpetes through a separate route.A nitrogen balance exists in organisms, when nitrogen intake (protein) equals  nitrogen excretion occurs but balanced.

some of the plant proteins are rumen degradable proteins while others may not be degraded (fermented & digested). such rumen undegraded proteins break down in the small intestine and are absorbed which leads to better performance. 

I hope that this text could be helpful for you http://babcock.wisc.edu/sites/default/files/de/en/de_05.en.pdf 

The amount of "rapidly" degraded protein (Nitrogen) in the rumen will probably be too high, even if the diet is isocaloric NFC will be lacking, meaning a lower production of microbial protein. Besides, some of the diet protein is normally not degraded in the rumen ("by-pass") and is digested in the intestine, this is lacking here. Finally, the high amount of Nitrogen (urea) that goes into the bloodstream needs to get rid of, and this requires a huge amount of energy.

There may be several answers to your question but a basic or fundamental answer is related to the energy costs to supply of essential amino acids for the animal. Supplying intact amino acids from protein translates to reduced microbial energy costs (carbon skeleton converted to CO2) required to synthesize protein needed from microbial growth. Protein produced from non-protein nitrogen requires the rumen bacteria to expend energy to synthesize all its amino acids rather than catabolize protein to extract a preformed amino acid or amino acid carbon structure. Secondly feeding intact whole protein can and does result in ruminal protein bypass that subsequently is hydrolyzed in the small intestine of the cow along with microbial protein. Ruminal bypass protein can be an important source of essential amino acids for the cow that exceed the normal microbial production. Therefore if the microbial community expends more effort degrading cellulose rather than building protein for its own growth rumen turnover of fiber is increased leading to more energy and amino acids being available to the cow for growth and production. Check the literature for CO2 and methane losses when cows are fed intact protein verses non-protein nitrogen.