Implementation of field cardio-respiratory measurements to assess energy expenditure in Arabian endurance horses

Measurements of respiratory exchanges in genuine exercise conditions are undoubtedly of interest to further define the energy needs of endurance horses. However, the equine K4b², the gas exchanges portable device validated for equines, has not been used in Arabian endurance horses yet. Therefore, the objective of this study was to implement field cardio-respiratory measurements in such horses using the equine K4b² in order to assess energy expenditure (EE). Measurements of heart rate (HR), oxygen uptake (VO₂), carbon dioxide production (VCO₂), respiratory frequency (RF), tidal volume (VT) and minute expired volume (VE) were carried out at rest and during a 20-min submaximal incremental field exercise in five trained Arabian endurance horses equipped with the K4b² system. The relationship between HR and VO₂ was determined for each horse. EE of the exercise session was calculated from direct VO₂ measurements and individual HR-VO₂ regression. Out of the five horses, four tolerated the equipment. Respiratory and metabolic variables at rest and during exercise, as well as EE measured at the different gaits, were consistent with reported values in exercising horses: VO₂ ranged from 4.8 to 54.1 ml/min per kg from rest to canter, respectively, and EE from 82 to 1095 J/min per kg BW. The 20-min exercise session EE accounted for 6258 and 6332 J from direct VO₂ measurements and individual HR-VO₂ regression, respectively, which did not differ significantly. Providing an adaptation period and several technical adjustments, the present equine K4b² could be used to assess EE in Arabian endurance horses in a controlled environment. The prediction of EE from the individual VO₂–HR relationship might be an alternative method to evaluate EE when VO₂ measurements are not possible.