Measuring Energy Use in Horses by Indirect Calorimetry

As they exercise, horses use various substrates, such as carbohydrates and fats, to fuel exercise. To determine the effects of different diets on exercise efficiency, researchers need to know which substrate is being used at a certain point in exercise.

Indirect calorimetry is the measurement of 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 Kentucky Equine Research, oxygen consumption and RER are measured using the 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 the athletic potential of each horse.

Learn more about Kentucky Equine Research here.