Tracing Acid-Base Variables in Exercising Horses: Effects of Pre-Loading Oral Electrolytes.

Oral electrolyte supplementation may influence acid-base state during exercise due to the intestinal absorption of administered water and electrolytes used to mitigating sweat losses. This study examined the effect of pre-exercise electrolyte supplementation (3 and 8 L) on plasma acid-base variables at rest, during moderate intensity exercise and during recovery. It was hypothesized that electrolyte supplementation will result in improved acid-base state compared to the alkalosis typical of prolonged exercise. In randomized crossover fashion, four horses were administered 3 L or 8 L of a hypotonic electrolyte solution (PNW) intended to replace sweat losses, or water alone (CON), 1 h before treadmill exercise to fatigue (at 35% of peak VO 2 ) or for 45 min at 50% peak VO 2 . Blood was sampled at 10-min intervals before, during and after exercise, and analyzed for dependent and independent acid-base variables. Effects of 3 L of supplementation at low exercise intensities were minimal. In the 8 L trials, plasma [H + ] decreased ( p < 0.05) during exercise and early recovery in CON but not PNW. Plasma TCO 2 decreased ( p < 0.05) by 30 min after PNW reaching a nadir of 28.0 ± 1.5 mmol/L during the early exercise period ( p = 0.018). Plasma pCO 2 and strong ion difference [SID] were the primary contributors to changes in [H + ] and [TCO 2 ], respectively. Pre-exercise PNW of 8 L intended to fully replenish sweat loses maintained [H + ], decreased [TCO 2 ] and mitigated the mild alkalosis during moderate intensity exercise.