Don’t forget to add Salt
Salt. Yes, table salt. Feed it daily.
You don't need to spend a fortune on horse-specific products to cover your horse's daily sodium. Head to your local market (or Costco) and buy it in bulk.
Sodium is critical for hydration, because water follows sodium. Sodium gets pulled across the gut wall by a transporter, and water follows by osmosis through channels called aquaporins (actually so cool).
Sodium also runs the electrical signaling that tells muscles to move. The sodium gradient across every cell membrane is what lets nerves fire. Without it, the brain can't tell the muscles what to do, and that includes the muscles running your horse's heart and pushing food through the gut, not just the ones under saddle.
Sodium works with potassium to power nerve signaling through cellular machinery called the sodium-potassium pump. The pump uses ATP, the cell’s energy currency, to push three sodium ions out of the cell and pull two potassium ions in, over and over. This sets up a gradient: sodium concentrated outside of the cell, potassium inside, both held like a loaded spring ready to act when needed.
When a nerve needs to fire, that spring releases. Sodium channels open and sodium rushes back in, which flips the electrical charge across the membrane and sends the signal racing down the nerve to the muscle. Right behind the sodium is potassium to resets the charge back to resting and readies the nerve for the next signal. The pump itself doesn’t send the signal but builds the gradient that makes signaling possible, working quietly in the background spending ATP to continuously reload the gradient so the spring is always ready.
Horses lose sodium fast through sweat, and their sweat is hypertonic, meaning it carries more salt per liter than human sweat does. After hard work or in the heat, that loss must be replaced, either through a salt lick or by top-dressing table salt.
At maintenance, horses need about 20 mg of sodium per kg of body weight per day. For the math-averse, that's 10 g of sodium a day for a 500 kg (1100 lb) horse. In work, or in extreme heat, that climbs to 60-100 mg/kg/day, or 30-50 g of sodium for the same horse.
One catch: that's sodium, not salt. Table salt is only about 39% sodium by weight, the rest being chloride, so it takes roughly 2.5 g of salt to deliver 1 g of sodium. That turns the maintenance requirement into about 25 g of salt a day, a little under 2 tablespoons. It turns the working requirement into 75-125 g, or 4 to 7 tablespoons.
That upper end is more salt than most horses will eat top-dressed in a single feed, which is why free-choice loose salt matters and why a horse working hard in heat and humidity needs an electrolyte supplement, not just a bigger scoop. If you reach for one, read the label and make sure it's mostly NaCl rather than sugar.
So which salt to choose?
Go with the one your horse will eat. Plain white salt, Himalayan pink, iodized table salt, they all work. You're after the sodium and chloride, each of these delivers it.
Iodized salt is what you'll find on most shelves, and that is fine. I promise not to go into a huge history lesson on why the majority of US markets stock iodized salt instead of non-iodized salt. Iodine is an essential mineral for proper thyroid function and most humans are deficient so it's added to nearly everything. If your horse is getting a fortified feed or balancer then iodine will already be covered so the iodine in the salt is immaterial.
Himalayan pink salt is also fine. The pink coloring comes from the trace minerals. Their amounts are too small to make a difference, so don't buy it thinking your horse will get a meaningful amount of the trace minerals, but you don't need to avoid it. If your horse doesn't eat plain white salt but eats the pink salt, buy the pink salt. The best salt is the one your horse will actually eat. Palatability beats purity in this case because sodium does nothing if the horse won't eat it.
Free-choice salt beats a salt block. Horses are fairly good at regulating their own sodium, so a covered bucket of loose salt they can help themselves to works well. They have a hard time licking meaningful amounts off a hard block because their tongues are smooth, so a block often can't keep up with what a working horse needs. If a block is all you can get, keep an eye on it. A horse that's gnawing it down is usually telling you it's short on sodium and not getting enough from the block, which is your cue to get loose salt in front of it.
Side note: sodium is the only mineral horses self-regulate well. They don't do this with any other mineral, so those free-choice mineral licks don't work the way people hope. A horse picks the one that tastes best, not the one it actually needs.
And always provide fresh, clean water. This matters more than it sounds. A horse can take in a large amount of salt and be completely fine as long as it can drink freely, because it simply drinks more and passes the excess. Salt only becomes dangerous when a horse loads up on it without enough water to balance it out. Water is the safety valve, so it should never be the thing in short supply.
