Validation of the oral 13C-bicarbonate tracer technique against indirect calorimetry for the estimation of energy expenditure in resting dogs

Knowledge on the energy requirements of horses is essential for optimal feeding practice. The ‘gold standard’ for measuring energy expenditure (EE) is indirect calorimetry where the horse has to be confined to a respiration chamber. Alternatively the 13C-bicarbonate tracer technique (13C-BTT) can be used to measure EE (Elia, 1991). After administration of a dose of 13C labeled sodium bicarbonate, the ratio between the 13C and 12C in spot samples of expired air collected over a sufficient period of time can be used to estimate the CO2 production rate (RCO2) and EE. Collection of breath samples can be done from the respiration chamber or it can be done under free living conditions with breath bags and a small mask. Combining measurements in the respiration chamber with the 13C-BTT makes it possible to compare the CO2 production measured with both techniques. Most studies in other species have used intravenous (IV) administration of 13C-bicarbonate (Urschel et al., 2009; Junghans et al., 2007). However, oral administration of 13C-bicarbonate in a single bolus could make the 13C-BTT totally non-invasive. The hypothesis is that the 13C-BTT with IV and oral administration of the tracer in a single bolus can be used for estimation of RCO2 and EE in sedentary ponies.