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Nucleic acid metabolism in the ruminant

2.* Formation of microbial nucleic acids in the rumen in relation to the digestion of food nitrogen, and the fate of dietary nucleic acids

Published online by Cambridge University Press:  09 March 2007

R. H. Smith  and
A. B. Mcallan
R. H. Smith
Affiliation:
National Institute for Research in Dairying, Shinjield, Reading RG 2 9AT
A. B. Mcallan
Affiliation:
National Institute for Research in Dairying, Shinjield, Reading RG 2 9AT
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Abstract

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1. Concentrations of nucleic acid nitrogen (NA-N) and other nitrogenous constituents were estimated in samples of rumen fluid taken from calves and cows which were either given stall diets of varying nitrogen content or were allowed to graze pasture. Concentrations of NA-N ranged from 1.5 to 27.5 mg/100 g water.

2. Ratios of RNA: DNA in rumen fluid were similar to those in rumen bacteria and were not related to those in the diets. Pure nucleic acids added to the rumen were rapidly degraded. It was therefore concluded that NA-N in rumen fluid was largely of microbial origin and provided an index of total microbial nitrogen.

3. In most experiments, with an individual animal consuming diets of various nitrogen contents, NA-N formed a fairly constant percentage (8-15 for different animals) of the total non-ammonia nitrogen in rumen fluid. This suggested that nitrogen entering the rumen fluid limited microbial growth. Consumption of a diet containing extracted decorticated groundnut meal (diet B), however, led to lower values for this percentage than did the other diets. Diet B was also exceptional in leading to marked diurnal variations in NA-N concentrations in rumen fluid, suggesting a cyclic fluctuation in the size of the microbial population.

4. Comparison of NA-N:total nitrogen ratios in rumen fluid and bacteria suggested that, for all the diets except diet B, 55–80 and 40–50% of the non-ammonia nitrogen in rumen fluid was of microbial origin for the calves and cows respectively.

Type
Research Article
Information
British Journal of Nutrition , Volume 24 , Issue 2 , June 1970 , pp. 545 - 556
Copyright
Copyright © The Nutrition Society 1970

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