Abstract
Rates of equilibration and subsequent wash-out of tritium were measured in parallel samples of blood, rumen fluid and faeces collected from two adult female Norwegian reindeer in summer and in winter. The tritium-concentration was the same in all three body water compartments after no more than 9 h following both intravenous and intra-ruminal injection of isotope in summer and following intravenous injection of isotope in winter. The biological half-life of the tritium increased from approximately 3 days in summer to approximately 10 days in winter, probably as a consequence of a decrease in water intake. There were no significant differences in disappearance rates of tritium from blood, rumen fluid and faeces within any of the six experiments. Fresh faeces is therefore a reliable source of body water that can be used in place of blood in studies of body water kinetics in reindeer, thus making it potentially possible to conduct such studies on truly free-living and undisturbed animals.
Highlights
Isotope dilution methods have been used to measure a variety of physiological parameters in reindeer including total body water and body water turnover rate ( r H 2 0 ) (e.g. Cameron & Luick, 1972; Holleman et al, 1982; Larsen & B l i x, 1985) which can, i n turn, be used to estimate body composition (e.g. Searle, 1970; Arnold et al, 1985; Sheng & Huggins, 1979; Rozeboom et al, 1994) and to calculate the rate of C 0 2 - production by the doubly labelled water method (Lifson & McClintock, 1966)
W e found substantial seasonal variation i n kT values, illustrated by the increase i n biological halflife (t1/2) of 3 H from 3.4 ± 0.8 (SD) days, n = 12 body water compartments/experiments in summer, to 10.4 ± 0.6 (SD) days, n = 6 body water compartments/experiments in winter (Table 2). In both animals ( B M approximately 85 kg), 3 H equilibrated between blood plasma, rumen fluid and faeces no more than 9 h after injection of 3 H 2 0 in both summer and winter
Fancy et al (1986) reported equilibration time of 3 H between blood and rumen fluid i n excess of 9 h i n reindeer inwin ter
Summary
Isotope dilution methods have been used to measure a variety of physiological parameters in reindeer including total body water and body water turnover rate ( r H 2 0 ) (e.g. Cameron & Luick, 1972; Holleman et al, 1982; Larsen & B l i x , 1985) which can, i n turn, be used to estimate body composition (e.g. Searle, 1970; Arnold et al, 1985; Sheng & Huggins , 1979; Rozeboom et al, 1994) and to calculate the rate of C 0 2 - production by the doubly labelled water method (Lifson & McClintock, 1966). Isotope dilution methods have been used to measure a variety of physiological parameters in reindeer including total body water and body water turnover rate ( r H 2 0 ) 15 (2), 1995 mental animal after which body water parameters can be calculated by measuring the subsequent decline in the concentration of the marker(s) in body water resulting from their wash-out. Blood or urine have most commonly been used as the source of body water in which the concentration of markers) is measured but this precludes working w i t h truly undisturbed animals because the collection of such samples usually requires restraint of the experimental animal. The aim of this study was to investigate whether water extracted from samples of fresh faeces can reliably be used in place of blood samples in studies of body water parameters in reindeer. Faeces samples were collected opportunisticollected from an experimental animal without dis- cally from the ground no more than 30 seconds after turbing it
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