P. Haggarty et al., VALIDATION OF THE DOUBLY LABELED WATER METHOD IN GROWING PIGS, American journal of physiology. Regulatory, integrative and comparative physiology, 36(6), 1994, pp. 180001574-180001588
The CO2 production (r(CO2)) of eight growing pigs was determined by co
ntinuous collection of CO2 over 21 days and simultaneously estimated u
sing the doubly labeled water (DLW) method. The aim was to assess the
accuracy of the method before and after correction for known sources o
f error and to test for any residual discrepancy arising from as yet u
nidentified sources of error. Mass spectrometer accuracy was verified
by analyzing serial dilutions of the dose material in the form of an a
rtificial decay curve; no significant bias was detected. The physiolog
ical errors were linearly dependent on weight gain. DLW-derived r(CO2)
(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 a
ccounted for -0.006 (methane), -0.032 (fecal H-2 losses), -0.108 (fat
synthesis), and -0.146 (changing pool size) l CO2/g wt gain. After cor
rection for these sources of error the DLW-derived r(CO2) differed fro
m the true value by -2 +/- 3% ingroup 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 sta
bility with or without correction. The precision estimates include bot
h dose and background errors and uncertainty in the correction factors
used. Strategies for optimizing precision are presented.