AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 6 1574-R1588, Copyright © 1994 by American Physiological Society
Validation of the doubly labeled water method in growing pigs
P. Haggarty, M. F. Franklin, M. F. Fuller, B. A. McGaw, E. Milne, G. Duncan, S. L. Christie and J. S. Smith
Rowett Research Institute, Bucksburn, Aberdeen, United Kingdom.
The CO2 production (rCO2) of eight growing pigs was determined by
continuous collection of CO2 over 21 days and simultaneously estimated
using the doubly labeled water (DLW) method. The aim was to assess the
accuracy of the method before and after correction for known sources of
error and to test for any residual discrepancy arising from as yet
unidentified sources of error. Mass spectrometer accuracy was verified by
analyzing serial dilutions of the dose material in the form of an
artificial decay curve; no significant bias was detected. The physiological
errors were linearly dependent on weight gain. DLW-derived rCO2 (corrected
only for fractionated water loss) underestimated the true value by 0.270 l
CO2/g wt gain or -8% in the restricted (group R) and -16% in the ad
libitum-fed (group AL) groups. Known sources of error accounted for -0.006
(methane), -0.032 (fecal 2H losses), -0.108 (fat synthesis), and -0.146
(changing pool size) l CO2/g wt gain. After correction for these sources of
error the DLW-derived rCO2 differed from the true value by -2 +/- 3% in
group R and 0 +/- 3% in group AL. Thus there was no significant bias in the
DLW method after correction for known sources of error, even during rapid
weight gain or at weight stability with or without correction. The
precision estimates include both dose and background errors and uncertainty
in the correction factors used. Strategies for optimizing precision are
presented.
