Sodium is the primary electrolyte in extracellular fluid, responsible for maintaining blood volume, regulating fluid balance, transmitting nerve impulses, and driving the thirst mechanism. Horses are unique among large herbivores in that their natural forage — grass and hay — is very low in sodium, providing only about 0.5 to 2 grams per kilogram of dry matter. This means every horse, whether resting or working, needs supplemental sodium in the form of a salt block or loose salt. Without it, horses become sodium-depleted, lose their thirst drive, drink less water, and risk dehydration even when water is freely available.
A resting 500kg horse needs about 10 grams of sodium per day — roughly two teaspoons of table salt (which is about 25 grams of sodium chloride). A plain white salt block or loose salt should always be available free-choice. Horses in moderate work may need 25 to 30 grams of sodium, and those sweating heavily can need 40 grams or more, provided through electrolyte supplements after exercise.
0.47% of daily nutrient intake
Sodium makes up 0.47% of your horse's total daily nutritional requirements by weight. That's a tiny amount — but it matters.
Reduced water intake despite availability, licking dirt or wood (pica), dull coat, reduced sweating, poor performance, and in chronic cases, reduced feed intake and weight loss. Because sodium drives the thirst mechanism, a depleted horse may not realize they are dehydrated.
Sodium excess is self-correcting in horses with free access to water — they simply drink more. Problems only arise if water is restricted while salt is available, which can cause salt poisoning with signs of colic, staggering, and neurological disturbance.
| Life Stage | Size | Min | Max | Unit | Notes |
|---|---|---|---|---|---|
| Adult | — | 10 | 15 | g | For a resting 500kg horse. Forage is naturally low in sodium, so supplemental salt is essential. A salt block or loose salt must always be available. |
| Working / Active | — | 20 | 45 | g | Working horses can lose 3-5g sodium per liter of sweat. At 10-15 liters per hour of hard work, losses add up fast. Supplement electrolytes after exercise. |
Source: NRC 2007
