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

Abstract

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.