The effect of level and type of dietary fiber on the hydration status of horses in response to dehydration and endurance exercise

Two experiments were conducted to evaluate the effects dietary fiber on hydration status in dehydrated and exercising horses. A third experiment investigated the effect of exercise on fluid absorption from the gastrointestinal (GI) tract.;Experiment 1 compared three diets using six horses in a Latin rectangle design to evaluate the effects of level and type of dietary fiber on hydration status in response to dehydration with furosemide. Two diets contained a high level of dietary fiber, one of which contained a higher proportion of soluble fiber. The third diet was low in total and soluble fiber. When the high fiber diet contained more soluble fiber, horses lost more body weight (fluid) in response to dehydration with furosemide without a proportional loss of plasma volume (PV).;Experiment 2 examined the effect of dietary fiber on body fluid compartment volumes and the response to dehydration and endurance exercise. Eight horses were fed a high or low fiber diet in a two-period, crossover design. A greater extracellular fluid (ECF) and GI fluid volume was observed when horses received the high fiber diet. In addition, they lost more body weight and ECF in response to dehydration and exercise, but experienced a similar loss of PV compared to the low fiber diet. Along with Experiment 1, these results suggested that fluid from the GI tract was more available to replenish circulatory losses resulting from dehydration and exercise when horses were fed a high fiber diet.;In Experiment 3, the effect of exercise on fluid absorption from the GI tract was evaluated in eight horses in a two-period, crossover design. The appearance of deuterium in plasma after deuterium oxide administration was used to represent the rate of fluid uptake from the GI tract at rest or during 60 min of low-intensity exercise. Exercise reduced the rate of deuterium accumulation in plasma indicating exercise reduced the rate of fluid uptake.;In conclusion, a higher level of dietary fiber and an increased proportion of soluble fiber could benefit horses competing in activities with high sweat losses. However, the rate of fluid absorption from the GI tract may be reduced during exercise.