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Prolonged Winter Undernutrition and the Interpretation of Urinary Allantoin:Creatinine Ratios in White-tailed Deer

Materials and Methods

Adult (≥1.5 years old) white-tailed deer (four pregnant females, three males) were maintained in outdoor pens (15.5 × 30.0 m) near Grand Rapids, Minnesota. The study period was 4 February - 5 May 1988. Monthly mean minimum and maximum temperatures from January to May were –23.3, –23.8, –9.9, –2.8, and 7.2C and –9.7, –6.8, 2.1, 12.7, and 24.1C, respectively (DelGiudice et al. 1994b).

Two males and two females were assigned randomly to the treatment group and one male and two females to a control group. Deer were fed a high-protein (11.1% crude protein), high-energy (12498 kJ digestible energy/kg) pelleted diet ad libitum until 11 February (DelGiudice et al. 1990, 1994a). Base-line data were collected on 4 February from 08:00 to 12:00. We anesthetized deer by injecting 100-150 mg xylazine HCl and 200-650 mg ketamine HCl. Deer were weighed and blood-sampled, and urine was collected by catheterization (DelGiudice et al. 1994b).

Treated deer were fed a low-protein (7.0% crude protein), low-energy (7942 kJ digestible energy/kg) pelleted diet at a restricted level of 0.2-1.0 kg per deer each day from 11 February to 5 May, except for 15-19 April (see below). Each control deer was fed the same diet ad libitum from 11 February to 15 April (DelGiudice et al. 1994b). We restricted all seven deer to 0.2 kg of feed per day from 15 to 19 April to simulate the acute severe nutritional restrictions that might accompany a snowstorm (DelGiudice et al. 1994b, 1998). We resumed ad libitum feeding for control deer from 19 April after handling to 5 May. Mean daily feed intake during the study was 0.53 kg (95% confidence interval 0.47-0.59 kg) and 0.28 kg (95% confidence interval 0.06-0.50 kg) for the control and restricted deer, respectively, and maximum cumulative mass loss was 17.0-32.2% in restricted deer versus 7.0-17.4% in control deer (DelGiudice et al. 1994b). MEI was calculated by multiplying digestible energy intake by 0.85 (Hobbs et al. 1982). We anesthetized and handled all deer from 11 February to 5 May as described above. Additional details are presented in DelGiudice et al. (1994b).

Chemical and statistical analyses

Urinary creatinine concentrations were determined spectrophotometrically with a ABA-100 bichromatic autoanalyzer using modifications of the method of Jaffe (1886). Urinary allantoin concentrations were assayed to the nearest microgram per millilitre using modifications of the colorimetric method of Young and Conway (1942). Allantoin concentrations are reported in micromoles of allantoin to micromoles of creatinine (A:C ratio) to correct for differences in hydration among individuals.

We analyzed the temporal patterns of recent (i.e., 2 days prior to handling) mean daily MEI (kJ/kg0.75 body mass) and urinary A:C ratio in deer of the two groups by fitting a mixed-effects repeated-measures analysis of covariance (ANCOVA) model to the log-transformed data (Ware 1985; SAS PROC MIXED, SAS Institute Inc. 1996). Fixed effects of the model were diet, time, time2, diet × time, and diet × time2. Deer were random "subject" effects in the model. We did not examine potential sex effects; however, data from the males were within the bounds of variability of those of the females (DelGiudice et al. 1994b, 1998). Heterogeneous autoregressive and compound-symmetry covariance structures were selected to account for within-deer correlations for MEIs and A:C ratios, respectively (Wolfinger 1993). Mixed-effects repeated-measures polynomial regression models were used to evaluate the dependence of the A:C ratio on recent MEI, percent body-mass loss, and urinary urea nitrogen:creatinine (UN:C) and 3-methylhistidine:creatinine (3-MeH:C) ratios in deer. In these cases, we used compound-symmetry covariance structures and fit the following polynomials:

Y = β0 + β1t + β2t2 + β3t3

where t is the time-dependent predictor (recent MEI, percent body-mass loss, urinary UN:C ratio, or urinary 3-MeH:C ratio). Null hypotheses (H0) tested included equality of initial or base-line (i.e., β0) MEI and A:C ratios of the control and restricted groups, as well as whether the temporal patterns of A:C ratios of control and restricted deer had slopes that departed linearly or curvilinearly from 0 (i.e., β1 = 0 and β2 = 0, respectively). We selected the highest order polynomial that was statistically significant (α = 0.05; Neter et al. 1990).

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