Ruminants....

Feed InVFAMicrobial ProteinVitamins

The nutrients presented to thecow or steer by the rumen arevery different than those enteringthe rumen as feed.

Digestion

Fermentation

All CHO must passthrough Pyruvate tobecome VFA

Some Basics

Nonstructural polysaccharidesStructural polysaccharides

VFA, H+

Pyruvate Lactate

Rumen pH must be defended in the face oforganic acids and H+ production to preventacidosis.

Rumen papillae epitheliumperforms at least 3 majorfunctions:

• protection• metabolism• absorption

VFA are absorbed passively; thus,the concentration gradient from lumento blood supply must be maintained. Metabolism of some VFA within thecells of the papillae help ensure agradient.

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

Some Basics

B. Rumen Development Begins Early

1. Depends on:

a. fibrous diet

b. inoculation

c. VFA stimulation

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

Some Basics

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.

Ruminants....

Ruminants....

• Incorporation of recycled nitrogen in theform of ammonia allows the daily flowof nitrogen into the duodenum to EXCEED nitrogen intake when the dietary protein content is held low.

Ruminants....

• Synthesis of microbial protein ammonia (NH3) is a key molecule

H3N-C-COO-H

+

R

Ruminants....

• Rumen bacteria use NH3-nitrogen as a source of amino nitrogen for synthesizing amino acids.

• ~40% of the bacterial protein nitrogenpasses through the rumen ammonia pool.

DiffusionSaliva

NPN (urea)

Degradableprotein

Recycled urea

Dietary NH3 Sources Endogenous Sources

All of these contribute to the pool of ammoniain the rumen

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

Ammonia enters the rumen from multiple sources...

CO(NH2)2

C

O

NH2 NH2

Urease produced by SOME rumenmicrobes adhered to the rumenepithelium cleaves amino nitrogenfrom blood urea and releases it asfree ammonia. The ammonia in theacid conditions of the rumen isionized (NH4

+) and trapped.Urease

Ammonia enters the rumen from multiple sources...

NH3

As microbialprotein

Absorption byrumen wall

Flushing to omasum

Trapped ammonia-N exits the rumen as protein, or ammonia for recyling

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Ammonia enters the rumen from multiple sources...

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

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)

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