Evaluation of the urinary allantoin:creatinine ratio as a nutritional index for elk

Abstract

We conducted experiments with captive female elk (Cervus elaphus) to explore the utility of allantoin:creatinine (A:C) ratios as a noninvasive index of nutrition in free-ranging ungulates. Pens of animals were assigned to one of four dietary treatments, each treatment being given to 6 animals. One treatment involved gradually increasing the daily metabolizable energy intake (MEI) from approximately 650 to 1200 kJ metabolizable energy (ME)/kg body mass (BM)0.75in weekly increments over 8 weeks. In a second treatment, daily MEI was decreased in a similar manner from approximately 900 to 250 kJ ME/kg BM0.75. Urine samples (96 in total) were collected from each animal in these treatments 5 days after each change in diet. Two additional treatments involved relatively large and abrupt changes in daily diet ranging from 120 to 500 kJ ME/kg BM0.75, with successive diets being alternately increased and decreased at 2-week intervals for 10 weeks. Urine samples (179 in total) were collected from each animal 3, 5, and 13 days after a dietary change was initiated. The underlying relation between A:C ratio and MEI was consistent among the four treatments and indicated that the urinary A:C ratio is a reliable index of dietary intake in elk across a variety of dietary regimes. A:C ratios responded relatively quickly to changes in diet, indexing the dietary intake of the animals during a several-day period immediately prior to the time the urine was voided. The results of this and previous studies indicate that the urinary A:C ratio has significant potential as a nutritional index for wild ruminants; however, we recommend additional research before the use of A:C ratios is integrated into ecological or management applications.