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The rumen is
inhabited by an diverse microflora, but the CNCPS has only 2 pools of
bacteria: The FC bacteria ferment fiber and the NFC bacteria utilize
non-fiber carbohydrates.
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These two types of
bacteria also have fundamental difference in nitrogen metabolism.
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The FC bacteria use
ammonia as a N source, do not take up amino nitrogen and never produce
ammonia.
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The NFC bacteria can
use ammonia, but they prefer amino nitrogen like peptide and amino
acids. If the rate of NFC carbohydrate
degradation is insufficient to drive protein synthesis, incoming amino acids
will be degraded and converted to ammonia.
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The growth rate of
both types of bacteria is dictated by the Kd values of each feed component.
The rumen submodel uses growth rate to
predict the amount of energy that is
available for growth and the amount that is expended on maintenance.
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Ruminal bacteria can
also dissipate energy in futile reactions that are called energy spilling.
NFC bacteria spill energy if they are deprived of amino N or ammonia N and
the Kd is faster than the growth rate.
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