The effect of form of nitrogen on the efficiency of protein synthesis by rumen bacteria in continuous culture.
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Date
1991
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Abstract
The aim of this study was to examine the effect of the form of
nitrogen available to mixed rumen bacteria on the efficiency of
microbial protein synthesis. A novel, solid substrate, continuous
culture fermentor which proved capable of maintaining
representative populations of mixed rumen bacteria under steady
state conditions, at predetermined growth rates was developed for
the study. A series of experiments wherein maize straw, alkaline
hydrogen peroxide-treated wheat straw, rye grass or a mixture of
maize straw and maize starch were used as substrates were
performed in the fermentor. The effect of supplementing these
substrates with different forms of nitrogen, namely peptides in
the form of a partial hydrolysate of casein, or ammonium salts
alone or ammonium salts plus branched-chain volatile fatty acids,
on digestion of the substrate and microbial protein synthesis was
investigated. Supplementation of maize straw with peptides
increased microbial protein synthesis, however this was only
significant (P<0.05) when the availability of nitrogen and
specific growth rate of the bacteria were not limiting. Organic
Matter digestion was not affected by peptide supplementation.
Replacement of casein hydrolysate with sunflower oilcake as a
source of amino acid nitrogen further increased microbial protein
synthesis. The form of nitrogen supplementation did not affect
the digestion of constituent cell wall monosaccharides of maize
straw. Supplementation of alkaline hydrogen peroxide-treated
wheat straw with either branched-chain volatile fatty acids or
casein hydrolysate increased the synthesis of microbial protein
significantly (P<0.05) and caused a slight, but insignificant
increase in the digestion of cellulose-glucose. The efficiency of
microbial protein synthesis on rye grass was high, relative to
the other substrates, and unaffected by the supplementation of
either branched-chain volatile fatty acids or peptides. On media
containing high levels of starch, microbial protein synthesis as
well as Organic Matter digestion were increased by peptide
supplementation, but these differences were only significant
(P<0.05) when the bacteria were growing at a high specific growth
rate. In all of these experiments, peptide supplementation was
accompanied by extensive degradation and deamination of amino
acids which offset any increase in microbial protein synthesis.
Peptide supplementation therefore resulted in far less efficient
overall utilization of protein.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.
Keywords
Rumen--Microbiology., Rumen fermentation., Nitrogen in animal nutrition., Proteins--Metabolism., Theses--Animal and poultry science.