Overwinter changes in the urine chemistry of muskoxen from Banks Island

The levels of various metabolites in urine have been used to assess winter nutritional deprivation in cell ids: however. few studies have assessed this technique for other ungulates. Between March 1993 and May 1998, we collected >400 snow-urine samples from muskoxen (Ovibos moschatus) on Banks Island. Northwest Territories, Canada. We determined urea nitrogen:creatinine (UN:C) and cortisol:creatinine (C:C) for each sample. Ratios of both UN:C: and C:C decreased from early to mid-winter and increased from mid- to late winter. The pattern of decreasing UN:C and C:C from early to mid-winter is different from that found in other studies and is not likely a reflection of superior animal condition in mid-winter: Muskoxen have a variety of physiological adaptations to minimize energy requirements and expenditures during winter, and these adaptations may cause the reduced UN:C and C:C we found during mid-winter. Urea N:C were greater for muskoxen in areas of high density and in years when winter forage quality was greater. Cortisol:creatinine ratios were greater during the winter when southern Banks Island experienced severe icing conditions. Our findings indicate these ratios may he useful measures on the ability of winter habitats to support muskoxen on Ran ks Island, provided winter forage quality is also measured. Whether UN:C of 4.0 mg/mg represents severe dietary restriction and possible starvation in muskoxen, as it does for bison (Bison bison). remains to be addressed.