An interesting aspect of athlete horse management is connected with the effects of the profuseThe energy required to power muscle activity in athlete horses is drawn from the diet and/or body stores via a comparatively inefficient process, since about 80% of this energy is lost in the form of heat [17]; h e a t i s d i s p e r s e d t h r o u g h f o u r f un d a m e n t a l mechanisms: irradiation, convection, conduction and evaporation.I n e q u i d s , s w e a t t h u s r e p r e s e n t s t h e m a i n thermoregulatory mechanism (55-60%), whereas losses through breathing account for about 25% [14]. Intense exercise may induce thermal stress; heat p r o d u c t i o n e x c e e d s d i s p e r s i o n i n a d v e r s e environmental conditions, e.g. high temperature and/ or humidity [18].According to McConaghy [17] horses, despite their double sweating ability, are more prone than man to thermal stress. According to McCutcheon and Geor [18], training and warm acclimation, by reducing the amount of sweat required to achieve thermoregulation, result in decreased loss of water and ions.Evaporation of 1 litre of sweat disperses the 580 kcal produced in 5-6 min of submaximal exercise (100 kcal/ min) or in 1-2 min of maximal effort (450 kcal/min) [17]. Thoroughbreds and trotters can lose up to 10 l in races of 1 or 2 miles (1,600-3,200 m), and 35-40 l in an endurance race of 5 hr in a temperate climate [14].Unless these heavy water losses are restored soon, severe dehydration may arise, with fatal consequences in 12-15% of cases.The effects of moderate dehydration in horses are probably similar to those observed in man, where impaired physical performances are seen already with losses accounting for 2-4% body weight [3]. The decrease in blood volume induced by dehydration entails decreased perfusion not only of muscles