Download Protein Digestion

Protein Digestion
1
N 0
N N 7
6
17
N N
N
1
4 1
7
N
N 2
1
17
N N
N 16
N 9 13
11 N
1
12
3 N
N 16
1
1
N
N
20
18 N
N
8 N N
N 19
7
N N
N 4 11
1
Crude Protein in feed is composed of both true proteins and
Non-protein Nitrogen. As illustrated in the diagram below,
true proteins are composed of long chains of amino acids.
13 N N
N 12
3
True proteins are composed
of long chains of amino acids.
The chain of each unique
protein (e.g., milk casein,
blood albumin) is a specific
sequence of 20 different
amino acids. Each amino acid
contains at least one atom of
nitrogen.
When feed proteins enter the rumen, those that are degradable
are broken down by microbial enzymes into shorter chains
(peptides), individual amino acids, organic acids and ammonia.
Rumen microbes use these breakdown products to
manufacture their own microbial protein. As digestion
progresses, microbes are carried out of the rumen. In the small
intestine, digestive enzymes release amino acids from
microbial protein for use by the cow. Undegradable feed
proteins pass through the rumen without being digested.
Unless they are completely resistant, they will also be digested
in the small intestine.
The blend of amino acids available to the cow is a combination
of those released by intestinal digestion of both microbial and
undegraded feed proteins. When the available blend is not
exactly what the cow requires, excess amino acids are broken
down in the liver, much of the nitrogen (N) being released as
urea and excreted.
Dietary Non-protein Nitrogen is rapidly and completely
degraded to ammonia by rumen microbial enzymes.
source: Dairy Production Primer - Feeds & Feeding Management
©2004 Western Dairy Science Inc.