1. Ruminants....

2. The nutrients presented to the cow or steer by the rumen are
Feed In
VFA
Microbial Protein
Vitamins
The nutrients presented to the
cow or steer by the rumen are
very different than those entering
the rumen as feed.

3. Digestion Fermentation All CHO must pass through Pyruvate to
become VFA

4. Some Basics Pyruvate Lactate VFA, H+
Nonstructural polysaccharides
Structural polysaccharides
Pyruvate Lactate
VFA, H+
Rumen pH must be defended in the face of
organic acids and H+ production to prevent
acidosis.

5. Rumen papillae epithelium
performs at least 3 major
functions:
protection
metabolism
absorption
VFA are absorbed passively; thus,
the concentration gradient from lumen
to blood supply must be maintained.
Metabolism of some VFA within the
cells of the papillae help ensure a
gradient.

6. Some Basics II. Rumen Development
A. Newborns are not functional ruminants
1. Lack sucrase
2. Limited amylase
3. Lactase: galactose, glucose
4. Ability to digest non-starch polysaccharides precedes that for starch

7. Some Basics B. Rumen Development Begins Early 1. Depends on:
a. fibrous diet
b. inoculation
c. VFA stimulation

9. Some Basics C. Inoculation occurs by: 1. Feed
2. Inter-animal contact (saliva)
3. Manure, soil
*occurs with isolation, but much slower and less completely

10. Ruminants.... N metabolism vs. Protein metabolism...
The quality and quantity of protein (amino acids) fed to the rumen is very different from that delivered to the small intestine because microbes within the rumen fix nitrogen and modify in coming proteins.

13. Ruminants....

14. Ruminants.... Incorporation of recycled nitrogen in the
form of ammonia allows the daily flow
of nitrogen into the duodenum to EXCEED nitrogen intake when the dietary protein content is held low.

15. Ruminants.... Synthesis of microbial protein
ammonia (NH3) is a key molecule R

16. Ruminants....
Rumen bacteria use NH3-nitrogen as a source of amino nitrogen for synthesizing amino acids.
~40% of the bacterial protein nitrogen
passes through the rumen ammonia pool.

17. Ammonia enters the rumen from multiple sources
Dietary NH3 Sources
Endogenous Sources
Diffusion
Saliva
Recycled urea
NPN (urea)
Degradable
protein
All of these contribute to the pool of ammonia
in the rumen

18. Ammonia enters the rumen from multiple sources...
The “urea cycle”
Carbomyl Phosphate + Aspartate + 3 ATP + 2 H2O
Urea + Fumarate + 2 ADP + 2 Pi + AMP + PPi

20. CO(NH2)2 O C Ammonia enters the rumen from multiple sources... NH2 NH2
Urease produced by SOME rumen
microbes adhered to the rumen
epithelium cleaves amino nitrogen
from blood urea and releases it as
free ammonia. The ammonia in the
acid conditions of the rumen is
ionized (NH4+) and trapped. C
NH2
NH2
Urease

21. Ammonia enters the rumen from multiple sources...
Trapped ammonia-N exits the rumen as protein, or ammonia for recyling
NH3
As microbial
protein
<
Absorption by
rumen wall
>>
Flushing to
omasum

22. Ruminants.... Ruminants do not require amino acids in their diet
Instead they require N
This N can come from amino acids or non-protein N (NPN) sources such as urea

23. Rumen undegradable proteins...
One of the challenges in formulating ruminant diets is that the AA ratio fed does not reflect the AA profile available to the animal
Therefore, there is interest in “Rumen Undegradable Proteins” (RUPs, RBPs)

24. Rumen undegradable proteins...
RUPs cannot be degraded by the microbes in the Rumen
Therefore, the amino content of the RUP represents what is being presented to the small intestine of the animal