BackgroundOverweight and obesity are the most common nutritional disorders in dogs and may lead to various secondary diseases and decreased lifespan. In obesity research, measurement of energy expenditure (EE) and determination of the energy requirements are essential. The objective with this study was to validate and evaluate the suitability of the oral 13C-bicarbonate technique (o13CBT) for measuring EE in dog obesity studies. A further objective was to investigate the impact of body weight (BW) reduction and changes in body composition on the EE when measured under conditions corresponding to the basal metabolic rate (BMR).ResultsThe EE in five privately owned, overweight dogs was measured simultaneously with the o13CBT and indirect calorimetry (IC) for comparison of the results. Two measurements per dog were performed under the same standardised conditions (i.e. fasted and resting state) at the start, and after completing a 12-week BW reduction program. Additionally, measurements of body composition by Dual-energy X-ray absorptiometry (DEXA) were conducted at the beginning and at the end of the BW reduction program. There were no differences in EE results obtained by the o13CBT and IC. Overweight and the BW reduction did not affect the estimates for the respiratory quotient (RQ) or the recovery factor for the 13C-tracer (RF), both needed when using the o13CBT. The dogs lost 16% (SD¿±¿2.0) of their initial BW in reduced fat mass (P¿<¿0.001), whereas fat free mass (FFM) remained unchanged. There was no effect of the BW reduction on the determined EE expressed in kJ/kg BW/d, or in kJ/kg BW0.75/d. However, EE was lower (P¿<¿0.001) after the BW reduction program when expressed in relation to FFM (kJ/kg FFM/d).ConclusionsResults from the present study show that the o13CBT can be a used in obesity research to determine EE in fasted dogs and under resting conditions. Furthermore, the results suggest that the BMR does not change with reduced BW in overweight dogs as long as the FFM remains unchanged. This indicates that the BMR to maintain one gram of fat is equal to maintaining one gram of FFM in overweight dogs.