Utilization of abomasally infused ribonucleic acid and deoxyribonucleic acid in sheep

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Virginia Polytechnic Institute and State University


Fifteen abomasally cannulated, growing wether lambs were used in two metabolism studies to evaluate the utilization of RNA and DNA. Wethers were blocked by weight and breeding and randomly assigned within block to one of five treatments with the restriction that no animal receive the same treatment in both trials. All animals were fed 350 g, twice daily, of a basal ration supplying 7.1 g nitrogen. In addition, the lambs received twice daily infusions of either soy protein, RNA, DNA, or a 1:1 combination of RNA and DNA or a sham infusion. Tris buffer was used as the solvent for RNA and DNA, the carrier for soy protein and the sham infusion. Infusions, except for the sham, were calculated to be isonitrogenous supplying 2.5 g nitrogen per day. Following a 10-day preliminary period, all urine and feces were collected during a 10-day collection period. Jugular blood was obtained at 6 and 12 hr post feeding on the last day of each trial. Crude protein digestibility was significantly elevated for the nucleic acid infusions over that for the sham. The RNA value, though not different from DNA or the combination, was comparable to that for the soy. Calculated by difference, the absorption values of RNA, DNA, and the combination of RNA and DNA were 97, 77, and 72%, respectively. Nitrogen retention, expressed in g/day, tended to be higher for the nucleic acids than for the sham. The combination of RNA and DNA was not different from the soy treatment which had the highest (P< .05) nitrogen retention. Urinary urea, allantoin, and ammonia levels were elevated (P <.05) for the nucleic acid treatments over the sham. Urinary creatinine and “other” nitrogen (nitrogen unaccounted for) were not affected by treatment. Blood urea.nitrogen tended to be higher for the combination of RNA and DNA than the sham, while RNA, DNA, and the soy treatments were higher (P <.05) than the sham. Serum protein concentrations were unaffected by treatment. The amino acid concentrations either tended to be higher or were higher for the nucleic acids, especially the RNA and combination of RNA and DNA, than for the sham. Concentrations for the nucleic acid treatments compared well with those for the soy treatment and in some cases were higher than the soy. From these data, the following conclusions were made: 1) nucleic acids are well digested and absorbed; 2) retention and utilization of nitrogen from nucleic acids appears to be minimal; 3) the majority of the absorbed nucleic acids are excreted as urea and allantoin; and 4) essential and non-·essential plasma free amino acids are increased by exogenous nucleic acids. The effect may be influenced by urea recycling to the rumen as the result of nucleic acid degradation. Urea recycling would stimulate microbial growth with consequent increases in microbial amino acid synthesis. Amino acids associated with the urea cycle were noted to be affected.