Evaluation of Urinary Indices of Nutritional Status for White-Tailed Deer: Tests with Winter Browse Diets

Abstract

Urea nitrogen:creatinine (U:C) and potassium:creatinine (K:C) ratios in nrine are used to assess nutritional status of white-tailed deer (Odocoileus virginianus) and other ungulates in winter. We evalnated the ratio of glucuronic acid:creatinine (G:C) in urine as a new index of diet quality and composition, and determined the effects of natural diets and food intake on G:C. U:C, and K:C ratios in winter. Glucitronic acid excretion reflects intake of plant secondary compounds and use of low-quality browse because conjugation with glucaronic acid is a major pathway of excretion of secondary compounnds. We fed a 100% deciduous browse diet and 3 diets each composed of 45% of the decidnons diet and 55% of 1 of 3 conifer browses (northern white tedar [Thuja occideutalis], castern hemlock [Tsuga canadensis], balsam fir [Abies balsamea]) to 6-7 fawus per diet in feeding trials in 1996 and collected nrine for analyses. We also analyzed urine samples from a similar set of trials in which 8 diets composed of varying proportions of decidnous browse, northern white cedar, and a small amount of lichen (Usitea spp.) were fed to deer in 1991. For the 1996 and 1991 trials, there were positive relationships (r 2 = 0.37-0.56) between G:C ratio and food intake for the pooled browse diets, Except for the 100% deciduous diet, there was a strong positive relationship (r 2 = 0.79) between G:C ratio and intake for each mixed diet in the 1996 trials. In the 1996 trials, deer fed the 55% balsam fir diet had a 2.9 times greater G:C ratio than all other diet groups, and the deciduous diet resulted in the lowest mean value. In the 1991 trials, deer fed diets with ≥55% northern white cedar had 1.7-3.2 times greater G:C ratio than those on thets with 5% or 30% northern white cedar. Urinary G:C ratio has potential as an indey of the proportion of deciduons and conifer browse in winter diets and as an index of the use of balsam fir Only deer with a high intake of balsam fir had G:C values >6. We found no evidence that U:C ratio was influenced by short-term ration in diet composition or food intake. We found high variability in the relationship of K:C ratio to food intake with winter browse diets, and we suggest cantion in using this index in field studies.