[The effect of energy concentration and source on the use of feed protein and NPN in lambs. 3. Allantoin excretion and microbial protein synthesis]. / Einfluss der Energiekonzentration und -quelle auf die Verwertung von Futterprotein und NPN bei Lämmern. 3. Mitteilung. Allantoinausscheidung und mikrobielle Proteinsynthese.

In an N balance experiment with male crossbreeding lambs at an age of 3 ... 4 months four different rations were given differing in energy concentration (high greater than 700 EFU cattle/kg DM and low less than 650 EFU cattle/kg DM) and in the energy source (sugar, starch or crude fibre) with crude protein intake being almost equal. The rations contained 2% urea. Microbial protein synthesis in the rumen was assessed according to ROTH and KIRCHGESSNER (1978) (1), RYS et al. (1975) (2) and BICKEL-BAUMANN and LANDIS (1986) (3) on the basis of allantoin excretion in urine. The highest ruminal protein synthesis quotas were 868 ... 921 mg protein N per kg LW0.75 in (2). In (3) 723 ... 766 mg protein N/kg LW0.75 were synthesized. From the 15N labelling of the supplemented urea and the excreted allantoin it could be calculated that 26 ... 40% of the microbial protein resulted from the urea-N of the ration. Despite a high crude protein content of the ration of between 16 and 17% in the DM and a relation of NPN: pure protein of 0.95 the utilization of the NPN in the ration was relatively high but slightly lower than the utilization of pure protein. The variants with higher energy concentration showed as a tendency higher allantoin excretion in spite of slightly lower dry matter intake and a slightly higher NPN utilization than the variants with lower energy concentration.

[Influence of energy concentration and source on the utilization of feed protein and NPN in lambs. 2. 15N balance and utilization of pure protein and NPN]. / Einfluss von Energiekonzentration und -quelle auf die Verwertung von Futterprotein und NPN bei Lämmern. 2. Mitteilung. 15N-Bilanz und Verwertung von Reinprotein und NPN.

In an experiment 12 lambs of the merino species were divided into 4 groups. The variants HE received 740 or 718 EFU cattle/kg DM and the variants NE 689 or 671 EFU cattle/kg DM. The different energy concentrations resulted from differentiated quotas of dried sugar beet chips and wheat starch supplements. Within the variants, sub-variants with (HESZ, NESZ) or without (HES, NES) sugar supplements were formed. Due to varied DM intake, the average energy intake in all groups was 42 EFU cattle/kg LW0.75. N balance experiments using 15N-labelled urea were carried out, and 15N accumulation of N excretion was projected to a steady state. The partial utilization of pure protein and NPN in the ration was ascertained with the help of a 3-pool compartment model of N utilization in ruminants. In the non-amino acid N pool HE utilized 84% of NPN and NE 77% for the synthesis of amino and nucleic acids. The efficiency of protein synthesis in the amino acid N-pool were in HESZ 64%, HES 70%, NESZ 70% and NES 73%, resp. The total utilization of NPN is the sum of the partial utilization in the two pools, whereas the total utilization of pure protein is calculated from the true digestibility and the efficiency of the utilization in the AA-N pool. The total utilization of NPN for the synthesis of protein for the protein pool amounted to 40/35/41/33% and that of pure protein to 54/51/49/50%. Energy intake being identical, energy concentration did not have an influence on the utilization of pure protein and NPN, whereas NPN utilization was better in rations containing sugar. The pure protein in the ration was by 19 ... 52% better utilized than NPN.