Do urinary urea nitrogen and cortisol ratios of creatinine reflect body-fat reserves in black-tailed deer?
Urinary ratios of urea nitrogen:creatinine and cortisol:creatinine have been used as indices of the nutritional and physiological health of cervid populations. These ratios are used to monitor temporal trends in dietary protein and (or) energy deprivation, and changes in net catabolism of endogenous protein as body-fat reserves are depleted. Over a 2-year period, we compared urine chemistries of free-ranging and captive Sitka black-tailed deer (Odocoileus hemionus sitkensis) to examine seasonal and locational differences. We also determined body composition of all deer using tritiated water. Elevated urea nitrogen and cortisol ratios of creatinine did not consistently reflect individual animal body condition as measured by declining fat content in our free-ranging animals. Instead these urinary ratios more likely reflect immediate dynamics between fat depletion, protein catabolism, and energy intake rather than long-term changes in body-fat reserves.