NITROGEN-METABOLISM AND REQUIREMENTS OF NITROGEN AND ENERGY IN THE WOMBATS (MARSUPIALIA, VOMBATIDAE)

The Wombats Vombatus ursinus and Lasiorhinus latifrons are grazing mar supials from mesic and xeric habitats, respectively. Four wombats of e ach species were fed pelleted isocaloric diets containing 1.0% and 0.6 % N. Urea kinetics (C-14-urea and N-15-urea) and whole-body protein tu rnover (N-15-glycine) were integrated into a model of N flow through p ools of amino acids, protein, and urea in the body. Maintenance dietar y N requirements were the lowest reported for herbivorous marsupials: 201 and 158 mg.kg-0.75.d-1 for Lasiorhinus and Vombatus, respectively. The mean maintenance energy requirement (140 kJ.kg-0.75.d-1) was only 32% of the estimate for macropod marsupials. Urea was recycled extens ively, with 64%-78% of synthesized urea degraded and 34%-42% reutilize d in the body. Rates of creatinine excretion and whole-body protein tu rnover were similar to those for macropods (4.06-6.66 g crude protein. kg-0.75.d-1), even though wombats excreted N-15-glycine slowly, indica ting that wombats have large protein pools, consistent with their musc ular conformation. The low requirements for N and energy enable the wo mbats to utilize poor-quality pastures and to exploit habitats where f ood abundance may be limited seasonally.