Urea and Other Nonprotein Nitrogen Compounds in Animal Nutrition (1976) / Chapter Skim
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MECHANISM OF NPN UTILIZATION IN THE RUMINANT
MECHANISM OF NPN UTILIZATION IN THE RUMINANT
Pages 3-16
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From page 3... ...
Results of similar studies have yielded information on the mechanism of NPN utilization and have provided the facts for establishing the guidelines for the use of NPN in practical ruminant rations. Urea was approved in the United States as a feed ingredient in ruminant diets in 1940 by the Association of American Feed Control Officials.
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From page 4... ...
NH3 + Keto Acids ^ - Amino Acids 4. Amino Acids ' Microbial Protein c »*
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From page 5... ...
The free amino acids and peptides may be incorporated into microbial protein or deaminated with the production of ammonia and volatile fatty acids (VFA) , which may be absorbed from the rumen or used by microbes as carbon skeletons for amino acid synthesis.
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From page 6... ...
The most important single fermentation characteristic is the amount of fermentable energy available in the diet for microbial growth (protein synthesis) above that needed for maintaining equilibrium in the rumen between the feed protein degraded and the microbial protein resynthesized.
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From page 7... ...
This system recognizes that microbial protein synthesis is primarily dependent upon energy availability and that the conversion of rumen degraded dietary protein into microbial protein represents an energy cost. Primary sources of carbon fragments that arise from carbohydrate fermentation are CO2 and VFA's.
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From page 8... ...
Minerals are required by rumen bacteria and the host animal, but substitution of NPN for dietary protein does not increase requirements for these beyond those stated in present feeding standards. Since NPN and grain are combined in a mixture to replace protein supplements in isonitrogenous diets, it must be remembered that this combination of NPN plus carbohydrate source may contain lower levels of essential minerals than does the replaced protein supplement.
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From page 9... ...
calculated that a dairy cow entirely dependent upon the microbial protein synthesized in the rumen for milk protein synthesis would produce only 10 kg of milk per day. This value is close to the quantity of milk actually produced by cows fed protein-free urea containing purified diets (Virtanen, 1966)
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From page 10... ...
protozoal protein found in rumen fluid and reported the following averages, respectively: crude protein content, 55 vs. 38 percent; true digestibilities, 66 vs.
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From page 11... ...
Replacement of dietary protein with NPN compounds increases the proportion of microbial protein and increases the nucleic acid content of protein presented to the abomasum and the small intestine. Protein requirements of ruminants, as is true of all animals, must be evaluated in terms of the amounts of amino acids absorbed from the intestinal tract in relation to those needed for productive purposes.
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From page 12... ...
These problems have been studied by different methods: Some have examined plasma amino acid profiles of ruminants receiving postruminal administrations of a single amino acid or mixtures of amino acids, while others have measured the performance of ruminants as well as monitored the plasma profiles. Treatment of dietary proteins to reduce or inhibit microbial degradation in the rumen has also been tested by others.
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From page 13... ...
Because gains were also lower in urea-fed steers, the importance of amino acid supplementation at the lower gut when urea is fed at high levels is emphasized. If further research identifies the amino acids needed by ruminants under specific conditions, development of products for incorporation in the diet to bypass degradation in the rumen appears feasible.
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From page 14... ...
An effective treatment for urea toxicity for cattle, if applied before tetanic spasms occur, is to immediately administer 20-40 liters of cold water orally. Cold water will lower ruminal fluid temperature and thereby reduce ureolysis.
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From page 15... ...
Also, there is simultaneous enzymatic hydrolysis of complex dietary carbohydrates to produce carbon skeletons, which combine with ammonia to form amino acids. These amino acids are used for the synthesis of microbial protein, which is later digested, absorbed, and utilized by the animal for productive purposes.
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From page 16... ...
Microbial protein contains about 20 percent nucleic acid, which is not utilized efficiently by the animal for protein synthesis. Also, the high proportion of cell walls in the microbes reduces protein quality.
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