Nitrogen Requirements and Urea Recycling in an Omnivorous Marsupial, the Northern Brown BandicootIsoodon macrourus

The maintenance nitrogen (N) requirement of the northern brown bandicoot,Isoodon macrourus, was determined by giving captive animals diets based on a commercial small carnivore mix and shredded sweet potato, with 20% sand included in the moist diet to simulate the soil ingested by bandicoots during natural foraging. Linear regression of N balance on N intake yielded maintenance N requirements of 438 mg kg−0.75d−1on a dietary basis and 413 mg kg−0.75d−1on a truly digestible basis. These values are high when compared with the range reported for other marsupial omnivores (46–146 mg kg−0.75d−1) and the omnivorous eutherian mouse (265 mg kg−0.75d−1). Possible reasons include an energy deficiency on the low and medium N diets that could have resulted in an overestimate of up to 45%, relative deficiencies of methionine and isoleucine in all diets (but the effect of these is difficult to quantify), high metabolic fecal nitrogen (MFN) due to the abrasive effect of sand on the digestive tract mucosa (but MFN was no lower without sand in the diets), or high rates of N loss in both feces and urine as seen in eutherian carnivores. The northern brown bandicoot is perhaps the most insectivorous of all peramelid marsupials, suggesting that the high maintenance requirements for N are an intrinsic characteristic of the species. Limited recycling of endogenously produced urea to the gut, only 28% on the low N diet, is consistent with this conclusion.