Plasma urea, creatinine, and urea: Creatinine ratio in reindeer (Rangifer tarandus tarandus) and in svalbard reindeer (Rangifer tarandus platyrhynchus) during defined feeding conditions and in the field

Variation in plasma urea and creatinine concentration and plasma urea : cre atinine ratio (U : C) were studied in semidomestic free-ranging reindeer (R angifer tarandus tarandus) on the Norwegian mainland, in wild Svalbard rein deer (Rangifer tarandus platyrhynchus), and in captive reindeer maintained either on a lichen-based diet or a protein-rich concentrate to investigate whether these parameters could be used as indicators of the nutritional sta tus of reindeer. In the mainland animals, plasma creatinine concentration w as high in winter and early spring and decreased by two-thirds toward the s ummer. The overall range in mean plasma creatinine concentration (+/-SE) wa s from to 90 +/- 1.26 to 280 +/- 2.88 mu mol/L. Mean plasma urea concentrat ion (+/-SE) varied from 2.46 +/- 0.10 in winter up to 17.44 +/- 0.29 mmol/L in summer and autumn. Month of sampling explained 65% and 90% of the varia tion in plasma urea and creatinine concentrations, respectively, indicating that seasonality in the diet had the greatest influence on these parameter s. Reindeer given lichens as the only feed showed an increase in plasma cre atinine and a decrease in plasma urea concentration. Food restriction cause d a temporary elevation in urea level but had no significant effect on plas ma creatinine concentration. The slight effect of energy intake on urea and creatinine levels was supported by the fact that severe undernutrition in the Svalbard reindeer population had only a small effect on plasma urea and creatinine levels. Protein-rich pellet feed increased plasma urea from aro und 3 mmol/L to above 10 mmol/ L and reduced creatinine concentrations to l ess than 100 mu mol/ L, suggesting that the protein content of forage is an important determinant of these blood parameters. Mean U : C ratio (+/-SE) in plasma varied from 8.9 +/- 0.28 120.8 +/- 1.88 Ratios above 20 appeared when protein intake was low and energy intake was restricted or when protei n intake was high. Low ratios occurred when protein intake was low but ener gy intake adequate. Plasma urea and creatinine concentrations and the U : C ratio showed complex dynamics that were affected by both season and the pr otein and feed intake. We conclude that they appear to be difficult to inte rpret as single measures of nutritional status of reindeer.