Urea utilization in growing lambs. 7. NPN- and pure protein-N-utilization at various ages

The utilization quota of NPN and pure feed protein for body protein synthesis was calculated on the basis of N balance experiments with 15N labelled urea with the help of model concepts of a 3-pool model and its mathematical usage. In lambs weighing 13 kg, the efficiency of amino acid and nucleic acid synthesis in the non-amino acid N pool was 64%. This results in a total utilization quota for NPN and pure protein in the ration of 40% and 60%, resp. Lambs weighing 27 kg showed an efficiency in amino acid and nucleic acid synthesis in the non-AA N pool of 77% and in the AA N pool of 60%. The total utilization quota of NPN was 47% and that of pure protein 56%. The pure protein in the ration was thus about twice as well utilized for total protein synthesis and for protein synthesis for crude protein retention as the NPN compounds in the ration.