Nitrogen Requirements and Urea Metabolism in Two Arboreal Marsupials, the Greater Glider (Petauroides volans) and the Brushtail Possum (Trichosurus vulpecula), Fed Eucalyptus Foliage

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Abstract
Maintenance nitrogen requirements (MNRs) were determined in greater gliders fed Eucalyptus radiata foliage and in brushtail possums fed E. melliodora foliage. Both species had high nitrogen requirements compared with most other marsupial species; the greater glider required 0.56 g truly digestible nitrogen · kg−75 · day−1 and the brushtail possum 0.42 g · kg−0.75 · day−1 to remain in zero nitrogen balance. The loss of nitrogen as ammonia in the urine was the major reason for the high nitrogen requirement of the greater glider. In contrast, excretion of fecal nitrogen, especially nondietary fecal nitrogen (NDFN), was responsible for the higher MNR of the brushtail possum, compared with previous estimates. This high NDFN excretion was partly attributable to the lack of selective retention of fine particles, including microbial cells, in the hindgut. Both species recycled large proportions of endogenously synthesized urea to the gut, but urea-synthesis rates were low compared with those found in other herbivores fed low-protein diets.