Oxygen consumption and gait variables of Arabian endurance horses measured during a field exercise test

P>Reasons for performing study: Arabian horses have morphological, muscular and metabolic features designed for endurance races. Their gas exchange and gait variables were therefore measured during a field exercise test. This study presents original respiratory and locomotor data recorded in endurance horses under field conditions. Hypothesis and objectives: Respiratory gas exchange ratio (RER) of Arabian horses at the speed required to win endurance races (18 km/h for 120-160 km) are < 1 and running economy (RE) is also low in order to maintain exercise intensity using aerobic metabolism for long intervals. The purpose of this study was to measure oxygen consumption and gait variables in Arabian endurance horses running in the field in order to estimate RER and RE. Materials and methods: Five Arabian horses trained for endurance racing were test ridden at increasing speeds on the field. Their speed was recorded and controlled by the rider using a GPS logger. Each horse was equipped with a portable respiratory gas analyser, which measured breath-by-breath respiratory variables and heart rate. The gait variables were recorded using tri-axial accelerometer data loggers and software for gait analysis. Descriptive statistics and linear regressions were used to analyse the speed related changes in each variable with P < 0.05 taken as significant. Results: At a canter speed corresponding to endurance race winning speed (18 km/h), horses presented a VO2 = 42 +/- 9 ml/min/kg bwt, RER = 0.96 +/- 0.10 and RE (= VO2/speed) = 134 +/- 27 l/km/kg bwt. Linear relationships were observed between speed and VO2, HR and gait variables. Significant correlations were observed between VO2 and gait variables. Conclusions and potential relevance: The RER of 0.96 at winning endurance speed indicates that Arabian horses mainly use aerobic metabolism based on lipid oxidation and that RER may also be related to a good coordination between running speed, respiratory and gait parameters.