The oral 13 C-bicarbonate technique for determination of energy expenditure in dogs: dietary and environmental factors affecting the respiratory quotient and 13 C recovery factor.

The oral 13 C-bicarbonate technique (o 13 CBT) can be used for short-term measurements of CO 2 production ( R CO 2 ) and energy expenditure (EEx). The method relies on appropriate estimates for the respiratory quotient (RQ) and recovery factor (RF) of 13 C. Four Retriever dogs were included in four experiments to validate the o 13 CBT against indirect calorimetry (IC), and determine RQ and RF; Expt. 1 : feeding different protein:fat:carbohydrate ratios [in % of metabolisable energy]: 25:33:42 in a maintenance (Mnt.) diet; 38:26:36 in a high-protein high-fibre (H Fibre ) diet and 27:56:17 in a high-fat (H Fat ) diet, simultaneously with start of measurements (T 0 ); Expt. 2 : the Mnt. diet at T 0 or 4 h postprandial (T 4 ); Expt. 3 : T 4 at different ambient temperatures, 22°C and 15°C; Expt. 4 : T 4 after 1 h physical activity. The R CO 2 and EEx were determined from the respiration chamber measurements made simultaneously with IC and the o 13 CBT (o 13 CBT online ), and in Expts. 1 and 2 , also on two consecutive days using o 13 CBT with collection of breath into breath bags (o 13 CBT breathbags ). The RQ values obtained at T 0 reflected dietary compositions, with the highest least square mean (LSM) of 0.954  for the Mnt. diet, 0.905 for the H Fibre and 0.877 for the H Fat diet ( p < 0.05). An increased interval between meal and measurement period decreased RQ significantly ( p < 0.05) in Expt. 2 , LSM being 0.954 at T 0 and 0.909 at T 4 . Ambient temperature ( Expt. 3) and physical activity ( Expt. 4 ) did not influence postprandial RQ. The RF values were not significantly affected by diet ( Expt. 1) . Measurements starting at T 0 ( Expt. 2 ) resulted in higher ( p < 0.05) RF values than at T 4 (LSM = 0.971 and 0.836, respectively). The ambient temperatures ( Expt. 3) did not influence postprandial RF. However, when dogs were physically active prior to measurements ( Expt. 4 ), RF values (LSM = 1.019) were higher ( p < 0.05) than when resting only (LSM = 0.836). Calculations based on RQ and RF determined in each experiment resulted in R CO 2 and EEx values which were not different regardless of method used, except for Expt. 1 where EEx-values [kJ · kg BW -0.75 · d -1 ] were higher ( p < 0.05) when measured with o 13 CBT breathbags (460) than by IC (421) and o 13 CBT online (420). Provided accurate RQ and RF values, the o 13 CBT breathbags can be used as an independent and minimally invasive research tool to determine EEx in dogs under carefully standardised conditions.