Réactions physiologiques face à des conditions extrêmes de chaleur et d'humidité relative. Etude de la récupération après l'exercice

The purpose of this study was to follow the recovery of horses during 1hour after treadmill exercise performed either in temperated atmospheric conditions (TC) (ambient temperature: 15°C; relative humidity: 55%) or in hot and humid conditions (HHC) (ambient temperature: 30°C; relative humidity: 75%). Five healthy fit standardbred horses (493± 14 kg; 4± 0,5 yrs) were investigated twice at eight days interval, in TC and in HHC. Some ventilatory and cardiorespiratory measurements were made during a standardised treadmill exercise test (SET), other measurements, i.e. cardiac and respiratory frequencies and rectal temperature, during a 1-hour recovery period. The SET consisted in 8 min warm-up and in 8 min exercise (1 min at 1,7, 4, 7, 8, 9 and 10 m/sec and 2 min at 4 m/sec with a 6% (3.4°) slope). Venous blond was sampled before, 2 min, 60 min and 48 hours after the completion of the test for biochemical analysis, namely plasma electrolytes and enzymatic activities. Exercising in HHC induced a reduction of the aerobic metabolism to the total energy requierement, i.e. a 20 % decrease of VO, and 55 % increase in lactate, as well as a decrease in VE. The increase in rectal and skip temperature, the dehydration and the weight loss were higher in HHC than in TC. During the recovery period the HR and f remained higher up to 30 minutes after the end of the SET in HHC while the rectal temperature remained higher up to 60 min after the end of this test. Sa, despite the fact that our horses recovered in TC after exercising in HHC, there were significant differences between their physiological parameters measured during the recovery. This means that the recovery in air-conditionned unit would probably be an insufficient measure to ensure an adequate cooling of the horses and justify consequently the adaptations proposed by the FEI, i.e. the decrease of the distance of the run and the increase of the lime devoted to the hall between phases