L. David Mech Ulysses S. Seal Glenn D. DelGiudice 1994 <p>Direct, practical means of assessing undernutrition in deer (<i>Odocoileus</i> spp.) and other ungulates during winter are needed in areas of research and management. We examined the relationship between mass loss and serum urea nitrogen (SUN) and urinary urea nitrogen:creatinine (U:C) in captive white-tailed deer (<i>O. virginianus</i>). During 4 February-5 May 1988, we maintained 7 adult white-tailed deer on various feeding regimes to simulate natural nutritional restriction during winter. Mass loss was greater (<i>P</i> = 0.037) in deer (17.0-32.2%) fed restricted amounts of a low protein low energy diet versus control deer (7.0-17.4%) fed the same diet ad libitum. Serum triiodothyronine (T3) concentrations did not differ (<i>P</i> = 0.191) between groups, but declined (<i>P</i> = 0.001) as nutrition declined. Slopes of percent mass lossSUN and urinary U:C relationships were positive <i>(P</i> = 0.008 and 0.055) in 7 and 6 deer, respectively. Mean U:C was directly related (<i>r</i>² = 0.52, <i>P</i> = 0.040) to mean cumulative mass loss, whereas mean SUN was not (<i>r</i>² = 0.29, <i>P</i> = 0.125). Data presented support the potential of urinary U:C as an index of winter nutritional condition of white-tailed deer; however, additional research is required to provide a complete understanding of this index's utility under field conditions.</p> application/pdf 10.2307/3809313 en Wiley Undernutrition and serum and urinary urea nitrogen of white-tailed deer during winter article