[The utilization of 15N-labeled urea by the laying hen. 3. Incorporation of labeled nitrogen into the amino acids of the white and egg yolk].

In an experiment with 3 colostomized laying hens the incorporation of heavy nitrogen from urea into the amino acids of the 21 eggs laid during the 8-day experiment was ascertained. In these eggs the content of 15 amino acids was ascertained separately in the whites and yolks of the eggs and their atom-% 15N-excess (15N') was determined. The heavy nitrogen could be detected in all amino acids investigated. The incorporation of 15N' into the essential amino acids of the white and yolk of eggs is very low. Of the applied 15N'-amount of the urea 0.18% could be detected in the 9 essential amino acids of the white of egg and 0.12% in those of the yolk. For the 6 analysed nonessential amino acids the rediscovery quota of 15N' in the white of egg was 0.50% and in the yolk 0.81%. The conclusion from these results is that the NPN-source urea is insignificant for egg protein synthesis.