Objective—To evaluate energy expenditure (EE) in
dogs by estimating rate of CO2 production (rCO2).
Procedure—Food was withheld for 24 hours, and all
dogs received an IV infusion of 13C sodium bicarbonate
for 8 hours. Breath samples were collected before
infusion and at 30-minute intervals from 4 to 8 hours,
and 13C enrichment in breath CO2 was measured,
using gas chromatography-isotopic ratio mass spectrometry.
Food was withheld from 6 dogs, and rCO2
and O2 consumption were measured, using a conventional
indirect calorimeter. The CO2 production and
O2 consumption were measured by use of indirect
calorimetry in 6 other fed dogs that were injected
with 2H2O and H218O. Blood samples were collected
before tracer injection, 4 hours later, and on days 4, 7,
and 11. Deuterium and 18O enrichments in plasma
water were determined.
Results—Mean rCO2 measured by indirect calorimetry
was 516 ± 34 and 410 ± 16 µmol/kg0.75/min in 6 fed
and 6 food-deprived dogs, respectively. The rCO2 calculated
from 13C-bicarbonate dilution was 482 ± 30
µmol/kg0.75/min. Mean rCO2 determined by use of the
double-labeled water method was 1,036 ± 46
mmol/kg0.75/d. Mean energy expenditure calculated
from rCO2 determined by infusion of 13C bicarbonate,
indirect calorimetry in fed and food-deprived dogs, and
infusion of double-labeled water was 386 ± 39, 379 ±
25, 338 ± 14, and 552 ± 25 kJ/kg0.75/d, respectively.
Conclusion and Clinical Relevance—Energy
expenditure calculated by indirect calorimetry in
unfed dogs can be considered representative of basal
metabolic rate. (Am J Vet Res 2002;63:111–118)