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Indirect Calorimetry - How Does It Work?By Kentucky Equine Research Staff · December 18, 2014

Indirect calorimetry is the measurement of heat produced by an animal through the determination of oxygen consumed and carbon dioxide eliminated.

Through indirect calorimetry, substrate utilization can be estimated using the respiratory exchange ratio (RER), calculated by dividing carbon dioxide produced (VCO2) with oxygen consumed (VO2). The nutritional RER range is 0.7 to 1.0, with 0.7 corresponding to predominantly fat utilization and 1.0 to predominantly carbohydrate utilization.

At Kentucky Equine Research, oxygen consumption and RER are measured using Columbus Instruments Oxymax system, an open-circuit indirect calorimeter that measures differences in ambient air that the horses inspire and expire while exercising. The horses wear a loose-fitting facemask while exercising, and expired gases are analyzed every 15 seconds throughout the exercise test. Oxygen consumption is reported on a body-weight basis (ml/kg/min), which allows direct comparisons to be made among horses and estimates athletic potential.

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