In Japanese quail ( Coturnix c. japonica; n = 9), the doubly labeled water (DLW) method (2H, 18O) for estimation of CO2 production (l/day) was validated. To evaluate its sensitivity to water efflux levels ( r H2 Oe ; g/day) and to assumptions of fractional evaporative water loss ( x; dimensionless), animals were repeatedly fed a dry pellet diet (average r H2 Oe of 34.8 g/day) or a wet mash diet (95.8 g/day). We simultaneously compared the novel infrared laser spectrometry (LS) with isotope ratio mass spectrometry. At low r H2 Oe , calculated CO2 production rate exhibited little sensitivity to assumptions concerning x, with the best fit being found at 0.51, and only little error was made employing an x value of 0.25. In contrast, at high r H2 Oe , sensitivities were much higher with the best fit at x = 0.32. Conclusions derived from isotope ratio mass spectrometry and LS were similar, proving the usefulness of LS. Within a threefold range of r H2 Oe , little error in the DLW method is made when assuming one single x value of 0.25 (recommended by Speakman JR, Doubly Labelled Water. Theory and Practice. London: Chapman & Hall, 1997), indicating its robustness in comparative studies.
Assessment of the amount of body water in the Red Knot (Calidris canutus): an evaluation of the principle of isotope dilution with2H,17O, and18O as measured with laser spectrometry and isotope ratio mass spectrometry
