[Studies on the protein and amino acid metabolism of laying hens receiving 15N-labelled casein. 5. 15N incorporation into different blood fractions and into the amino acids lysine, histidine and arginine contained in these fractions].

4 colostomizted laying hens were fed 15N labelled casein as a sole source of protein for a period of 6 days. The birds were slaughtered 2 or 6 days after receiving 15N dose. The blood was separated into corpuscular blood components and blood plasma. Then, the amount and content of nitrogen in the blood, the blood fractions and in the amino acids lysine, histidine and arginine and the excess of 15N atom% (15N') were estimated. The average N concentrationin the blood was 3.8%. The crude protein in the blood corpuscles contained 8.7% lysine, 7.1% histidine and 6.4% arginine; the corresponding values for crude plasma protein were 6.3%, 2.2% and 5.7%. The 15N atom% in blood nitrogen was found to be lower in the hens slaughtered 144 hrs after receiving the last 15N dose than in the birds already slaughtered after 48 hrs. The same trend was found for the plasma proteins. The level of excess 15N atom% in the blood corpuscles increased with the length of time elapsing after the withdrawal of 15N casein (over the period of time investigated); a decrease of excess 15N atom% in plasma lysine was noted, however, for the investigated period of time after the last 15N dose. In the corpuscular blood components a higher level of 15N atom% was usually found in histidine relative to that in lysine and arginine; it was higher in the hens slaughtered 6 days after receiving the final 15N dose than in the hens killed 2 days after administration of the last 15N dose.