AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 1 143-R149, Copyright © 1986 by American Physiological Society
Validation of doubly labeled water method using a ruminant
S. G. Fancy, J. M. Blanchard, D. F. Holleman, K. J. Kokjer and R. G. White
CO2 production (CDP, ml CO2 . g-1 . h-1) by captive caribou and reindeer
(Rangifer tarandus) was measured using the doubly labeled water method
(3H2O and H2(18)O) and compared with CO2 expiration rates (VCO2), adjusted
for CO2 losses in CH4 and urine, as determined by open-circuit
respirometry. CDP calculated from samples of blood or urine from a reindeer
in winter was 1-3% higher than the adjusted VCO2. Differences between
values derived by the two methods of 5-20% were found in summer trials with
caribou. None of these differences were statistically significant (P
greater than 0.05). Differences in summer could in part be explained by the
net deposition of 3H, 18O, and unlabeled CO2 in antlers and other growing
tissues. Total body water volumes calculated from 3H2O dilution were up to
15% higher than those calculated from H2(18)O dilution. The doubly labeled
water method appears to be a reasonably accurate method for measuring CDP
by caribou and reindeer in winter when growth rates are low, but the method
may overestimate CDP by rapidly growing and/or fattening animals.
