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What Is Indirect Calorimetry?By Kentucky Equine Research Staff · August 6, 2014

As a part of some studies conducted at Kentucky Equine Research (KER), it’s necessary to find out how different feeds influence the heat produced when a horse exercises. In other studies, it’s helpful to know when a horse switches from burning carbohydrates to utilizing stored fat for energy during exercise.

Indirect calorimetry is a way to quantify heat produced by an animal through the determination of oxygen consumed and carbon dioxide eliminated. Additionally, 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 KER, horses wear a loose-fitting facemask while exercising on a high-speed treadmill. Oxygen consumption and RER are measured using a Columbus Instruments Oxymax system, an open-circuit indirect calorimeter that measures differences in ambient air that the horses inspire and expire while exercising. 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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