Purine Derivatives in Snow-Urine as a Dietary Index for Free-Ranging Elk

Abstract

Vagnoni et al. (1996) performed experiments with captive elk (Cervus elaphus) that demonstrated a correlation between excretion of the purine derivative allantoin in urine and intake of digestible dry matter, suggesting urinary purine derivatives may be potential dietary indices for wild ruminants. To further explore the potential of urinary purine derivatives we collected sequential snow-urine samples from 5 free-ranging radiocollared cow elk in Yellowstone National Park (NP) during the winters of 1991-92, 1992-93, and 1993-94. A total of 116 snow-urine samples were assayed to determine concentrations of creatinine and allantoin, with 72 of the samples also assayed for other purine derivatives. Allantoin consistently accounted for >70% (x = 80.3%, SD = 8.7%) of total urinary purine derivatives and was correlated with other purine derivatives, indicating that measurement of allantoin adequately indexed total urinary purine derivative concentration. Allantoin: creatinine ratios (A: C) were calculated as an index of digestible dry matter intake, with creatinine standardizing allantoin concentration for differences in hydration and body size among animals, and the dilution effects of snow. The seasonal patterns in In(A:C) ratios followed the predicted U-shaped pattern, with lowest values occurring in midwinter and significantly higher values in December and April (P ≤ 0.001). This seasonal pattern generally remained consistent among winters despite substantial differences in mean annual In(A: C) values among all 3 winters. The lowest annual values were recorded for the winter of 1992-93 and the highest for the winter of 1993-94. Annual differences in A:C ratios corresponded with annual variations in winter severity, as indexed by measurements of snowpack and decreases in calf:cow ratios each winter. The results of this exploratory study suggest that urinary A: C ratios derived from snow-urine samples may be a useful noninvasive dietary index for free-ranging ruminants. Additional research, however, will be required to fully assess its utility.