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

Introduction


Obvious management implications of the relationship of winter nutrition to the performance of northern ungulate populations have prompted broad and intensive study of the effects of nutritional restriction on physical condition and physiological indicators of nutritional status. Two primary objectives have been to identify characteristics and means of data collection that would facilitate sensitive, practical, and cost-effective assessments of nutritional restriction or condition.

Collection and chemical analysis of urine in snow (snow-urine) has potential as a practical, non-invasive means of assessing the nutritional status of northern ungulates (DelGiudice et al. 1988, 1989, 1991, 1994a, 1995, 1997; DelGiudice 1995; Garrott et al. 1996; Moen and DelGiudice 1997; Ditchkoff and Servello 1999; Pils et al. 1999). During the past 2 decades, chemicals in the urine of wild ungulates have been studied under controlled and field conditions to evaluate their potential for use in nutritional assessments. Most recently, urinary allantoin, expressed as the allantoin:creatinine (A:C) ratio, has been proposed as an indicator of recent (2-3 days prior to urination) metabolizable energy intake (MEI) by elk (Cervus elaphus) during winter (Vagnoni et al. 1996; Garrott et al. 1997). Urinary allantoin is an end-product of metabolism of purine bases that are derived from nucleic acid catabolism during tissue turnover, from digestion of nucleic acids in feed, and from ruminal microbial fermentation of nucleic acids, which is directly affected by the animal's nutritional plane (Antoniewicz and Pisulewski 1982; Chen et al. 1990a, 1990b; Puchala and Kulasek 1991).

Vagnoni et al. (1996) and Garrott et al. (1997) reported positive correlations of A:C ratios with recent energy intake of elk experiencing body-mass gains and maximum mean mass losses of 9-11%. However, because free-ranging ungulates lose up to 33% of their body mass during winter (Davenport 1939; Moen and Severinghaus 1981; Severinghaus 1981; DelGiudice et al. 1992), Vagnoni et al. (1996) emphasized the importance of carrying out additional studies of cervids that would improve our understanding of endogenous contributions to urinary allantoin excretion associated with severe nutritional restriction and body-condition deterioration. This is especially critical to reliable interpretations of A:C ratios from snow-urines of free-ranging cervids.

Urinary allantoin has been studied more thoroughly in domestic ruminants, whose 24-h excretion was also positively correlated with energy intake over short time periods when there was little change in physical condition (Chen et al. 1990a, 1990b, 1992; Verbic et al. 1990; Giesecke et al. 1993, 1994; Puchala et al. 1993). Cattle and sheep fed maintenance diets have shown pronounced species differences in endogenous allantoin excretion, and the effects of short-term fasting on allantoin excretion have been inconsistent (Walker and Faichney 1964a, 1964b; Rys et al. 1975; Antoniewicz and Pisulewski 1982; Fujihara et al. 1987; Chen et al. 1990a, 1990b; Puchala and Kulasek 1991). None of these studies involved prolonged nutritional restriction or broad ranges of body-mass loss.

In the light of previous findings, we hypothesized that when animals primarily experience varying degrees of nutritional restriction and prolonged undernutrition accompanied by greater body-mass losses than have been reported thus far, the relationship between MEI and urinary excretion of allantoin (or A:C ratio) may be less apparent. Consequently, our objective in this preliminary effort was to assess the effect of long-term moderate and severe winter nutritional restriction on urinary A:C ratios of captive white-tailed deer (Odocoileus virginianus) and relate these ratios to MEI, body-mass loss, and other indicators of nutritional status.


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