PURINE DERIVATIVES IN SNOW-URINE AS A DIETARY INDEX FOR FREE-RANGING ELK

Vagnoni et al. (1996) performed experiments with captive elk (Cervus e laphus) that demonstrated a correlation between excretion of the purin e derivative allantoin in urine and intake of digestible dry matter, s uggesting 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-ra nging radiocollared cow elk in Yellowstone National Park (NP) during t he winters of 1991-92, 1992-93, and 1993-94. A total of 116 snow-urine samples were assayed to determine concentrations of creatinine and al lantoin, with 72 of the samples also assayed for other purine derivati ves. Allantoin consistently accounted for >70% ((x) over bar = 80.3%, SD = 8.7%) of total urinary purine derivatives and was correlated with other purine derivatives, indicating that measurement of allantoin ad equately indexed total urinary purine derivative concentration. Allant oin: creatinine ratios (A:C) were calculated as an index of digestible dry matter intake, with creatinine standardizing allantoin concentrat ion for differences in hydration and body size among animals, and the dilution effects of snow. The seasonal patterns in ln(A:C) ratios foll owed the predicted U-shaped pattern, with lowest values occurring in m idwinter and significantly higher values in December and April (P less than or equal to 0.001). This seasonal pattern generally remained con sistent among winters despite substantial differences in mean annual l n(A:C) values among all 3 winters. The lowest annual values were recor ded for the winter of 1992-93 and the highest for the winter of 1993-9 4. Annual differences in A:C ratios corresponded with annual variation s in winter severity, as indexed by measurements of snowpack and decre ases in calf:cow ratios each winter. The results of this exploratory s tudy suggest that urinary A:C ratios derived from snow-urine samples m ay be a useful noninvasive dietary index for free-ranging ruminants. A dditional research, however, will be required to fully assess its util ity.