The influence of dietary nucleic acids on the nitrogen metabolism in growing rats
Greife, H.A.; Molnar, S.
Zeitschrift fuer Tierphysiologie Tierernaehrung und Futtermittelkunde 43(4-5): 213-229
In a balance trial with 35 growing rats (5 groups of 7 animals each; initial weight 108.7 g) the influence of dietary nucleic acids on N metabolism was tested. The 9 day balance period was divided into 3 collection periods of 3 days each. The control ration contained casein + 5% DL-methionine as the sole protein source (1.64% N dry matter). To this basic ration RNA from yeast was supplemented at increasing levels of 7.8, 15.6, 23.4 and 31.2% of the diets N. The portion of daily feed intake and N intake derived from the basal diet was 10 g and 164 mg, respectively. RNA was ingested in addition. N digestibility and N balance were determined for each collection period. The excretion of the N compounds urea + NH3, allantoin, uric acid and creatinine was only analyzed for the total balance trial. Supplementation of RNA did not influence fecal N-excretion. The mean digestibility of RNA-N was determined as 95.8%. In the 1st collection period > 20% of the RNA-N ingested was retained. In the following 2 collection periods the RNA-N intake caused an additional urinary N-excretion of 36% and 62%. Utilization of the N derived from casein + DL-methionine was reduced by the RNA supplies. The animals apparently were still not adapted to the high RNA-N intake. In the total balance trial of 9 days duration 123% of the RNA-N consumed were excreted via kidneys, 97.4% as urea-N + NH3-N, 25.8% as allantoin-N and 0.5% as uric acid-N or creatinine-N. The excretion of RNA-N with the N-compounds is discussed with the values calculated from the metabolic pathways of the purines and pyrimidines.