Electrolytes and sweating — why a salt lick falls short in summer

In summer and under athletic load, sweating is the most important way by which the horse gives off heat. Unlike in humans, horse sweat is hypertonic — it contains higher electrolyte concentrations than the blood plasma. With the sweat the horse therefore loses not only water, but disproportionately salts, above all sodium and chloride.

Why pure water is not enough

It is exactly this hypertonicity that is the crux. Whoever after intense work only refills water dilutes the already lowered electrolyte levels further — the thirst stimulus eases before the salt balance is restored. A salt lick covers the basic sodium requirement and supports a sufficient water intake, but reaches its limit with high sweat losses: the amount taken up voluntarily is limited and the lick supplies above all sodium chloride, hardly any potassium.

Three electrolytes are to the fore. Sodium and chloride form the main share of the sweat loss and are replaced together as sodium chloride. Potassium is also lost, but is in part already well covered via forage-focused rations — with very high losses it nonetheless belongs in the replacement. A well-considered electrolyte balancing reproduces these losses in their composition, instead of just pushing in table salt.

Timing and water belong together

Electrolytes only work with sufficient water. Highly concentrated doses on an empty, poorly watered stomach can irritate the digestive tract; sensible is the administration dissolved or in the feed and always with free access to water. With long load — endurance, eventing, hot competition days — the replacement is spread over the work and the recovery, instead of giving everything at once. Routinely, a freely accessible salt source plus needs-based supplementation on sweating days is the everyday line.

Magnesium appears on many electrolyte mixes too, because small amounts are also lost via sweat and the requirement rises slightly with work and sweating. The main loss, however, lies clearly with sodium and chloride; an additional magnesium dose is no performance or calming lever in the sufficiently supplied horse. It is sensible when the overall ration shows an actual gap — that is clarified by the ration assessment.

The rule of thumb for hot days is thus unspectacular, but robust: plenty of water, a reliable salt source and on real sweating days an electrolyte replacement that reproduces the hypertonic composition of the sweat. Pure water or a lick alone do not carry the summer in sport.