Gastric Emptying and Intestinal Absorption of Electrolytes and Exercise Performance in Electrolyte-Supplemented Horses

1. Introduction

Horses lose considerably more electrolytes through sweating during prolonged exercise than can be readily replaced through feeds.

2. Materials and Methods

The present study tested an oral electrolyte supplement (ES) designed to replace sweat electrolyte losses. We measured gastric emptying of 3 L of ES (using gamma imaging of ⁹⁹Tc-sulfide colloid), the absorption of Na⁺  and K⁺  from the gastrointestinal tract using ²⁴Na⁺  and ⁴²K⁺ , and the distribution of these ions in the body by measuring radioactivity within plasma and sweat during exercise. Three liters of ES emptied from the stomach as fast as water, with a half-time of 47 minutes, and appeared in plasma by 10 minutes after administration. Peak values of plasma ²⁴Na⁺ and ⁴²K⁺ radioactivity occurred at 20 to 40 minutes, and a more rapid disappearance of K⁺  radioactivity from plasma was consistent with movement of K+  into cells. In a randomized, crossover experiment, 1 hour after administration of placebo (water, 1 L) or 1 L or 3 L of ES containing ²⁴Na⁺ , horses exercised on a treadmill at 30% of peak VO₂ until voluntary fatigue. Means were compared using repeated-measures ANOVA. 

3. Results and Discussion

²⁴Na⁺ appeared in sweat at 10 minutes of exercise and when horses received 3 L of ES the duration to voluntary fatigue was increased in all horses by 33 ± 10%. It is concluded that an oral ES designed to replace sweat ion losses was rapidly emptied from the gastrointestinal tract, was rapidly absorbed in the upper intestinal tract, and was rapidly distributed within the body. The ES clearly served as a reservoir to replace sweat ion losses during exercise, and administration of ES before exercise resulted in increased duration of submaximal exercise.