Abstract :
Athletic performance may be initially enabled but then become limited by changes in body fluids. This subject is reviewed in three parts: physiological responses, replacement strategies, and the influences of nutrition and feeding management. Emphasis on losses in sweat during strenuous exercise have focused attention on replacement of water and electrolytes, but the economies of water and energy are intertwined, so our interest should expand to the whole diet and its management. Feed balanced for strenuous exercise must maximize the conversion of its potential chemical energy into kinetic mechanical energy, and minimize waste such as feces, acid and heat. Research suggests five efficiency promoting tentative features: strong cation-anion balance (200-300 mEq/kg dry matter); modest protein (80-100 g/kg); ample vegetable oil (100-120 g/kg); specified fibers (difficult to quantify simply); and a stress profile of other essential nutrients (tentatively 1.5- to 3-times higher than currently recommended on a digestible energy basis). In effect, such an ergogenic feed replaces starch and sugar with fat and fiber. A high fiber intake increases water intake, gut water and net water absorption during strenuous exercise. It also increases heat production and water needed for evaporation, bowel ballast and fecal water output. Feeding management before an event involves the timing, size and nature of meals and watering. It should be adapted to the individual horse during training. Our laboratory has developed two complete and balanced ergogenic feeds, one for the stall-kept athlete, the other for the horse on pasture. Use of high-efficiency feeds like these should enhance the homeostasis of body fluids during strenuous exercise.
