The maintenance baseline and the three things that cover it before you consider additional supplementation.
Most horse owners walk out of a feed store feeling like they’re underdoing it. The aisles are long, the marketing is confident, the labels are dense, and the implicit message is that figuring out what a normal horse needs to eat requires a chemistry degree, a calculator, and a hay analysis.
The published reference standard for equine nutrition tells a quieter story. For a horse at maintenance — a normal horse doing normal horse things, not in heavy competition or hard daily work — the entire daily mineral and vitamin package is largely handled by three things most owners are already doing. Adequate forage. A ration balancer fed at the recommended rate. One to two tablespoons of plain iodized salt on the feed.
That is the foundation. It is not “most of what your horse needs” or “a good starting point.” For a maintenance horse, the foundation is sufficient on its own. The National Research Council’s Nutrient Requirements of Horses (6th rev. ed., 2007) lays out exactly what a maintenance horse needs each day. The forage analysis literature lays out exactly what a normal flake of grass hay delivers. Side by side, the math is clean.
This piece walks through that math. It also draws a clear line between maintenance and everything else, because there are real, evidence-supported reasons to add specific supplementation for certain horses, and those decisions deserve their own conversation but that determination is above the foundational needs, and the supplement aisle has done horse owners a disservice by blurring the two.
What the NRC says a maintenance horse needs
The National Research Council publishes the foundational reference document for equine nutrition. For an 1,100-pound (500 kg) mature horse at maintenance — no work, no lactation, no growth, no significant heat or cold stress — the published daily requirements for the major minerals are approximately:
| Mineral | Daily requirement (1,100 lb maintenance horse) |
|---|---|
| Sodium | ~0.35 oz (10 g) |
| Chloride | ~1.4 oz (40 g) |
| Potassium | ~0.9 oz (25 g) |
| Calcium | ~0.7 oz (20 g) |
| Phosphorus | ~0.5 oz (14 g) |
| Magnesium | ~0.26 oz (7.5 g) |
Mineral requirements are conventionally reported in grams because that’s the unit the NRC tables and the underlying research literature use. Ounce equivalents are included for everyday reference.
The full NRC tables also publish requirements for trace minerals (copper, zinc, selenium, iodine, manganese, iron, cobalt) and the fat-soluble vitamins (A, D, E, K), with adjustments for working horses, lactating mares, growing horses, and other categories at elevated needs. Those numbers are the floor. Every other claim in this piece is measured against them.
What forage already delivers
Forage is the foundation laid on top of the floor. And the foundation covers more of the requirement than most owners realize.
Potassium is the cleanest example. Analysis of mixed grass hays at commercial forage labs consistently shows potassium content in the range of 1.2 to 2.5% of dry matter, with some samples running higher. A horse eating about 22 pounds of typical grass hay per day — a normal amount for an 1,100-pound horse — is consuming roughly 4 to 9 ounces of potassium daily. That’s six to ten times the maintenance requirement of about 0.9 ounces. The Merck Veterinary Manual states the conclusion directly: a ration containing at least 50% roughage provides more than sufficient potassium for maintenance animals.
Potassium deficiency in horses on adequate forage is genuinely rare. The exception is horses doing significant sweat-loss work, who can lose meaningful potassium through hypertonic equine sweat — but that’s a different physiological state from maintenance, and it has different management. (That conversation belongs in the electrolytes piece, not here.)
Calcium and magnesium are similar stories. Calcium content in forage runs typically 0.3 to 1.5% of dry matter (higher in legumes like alfalfa, but adequate even in grass hays for a maintenance horse). Magnesium follows the same pattern. A horse on 22 pounds of grass hay is generally getting roughly 1 to 3.5 ounces of calcium and 0.4 to 0.9 ounces of magnesium daily, against requirements of about 0.7 oz and 0.26 oz respectively. Forage handles the macromineral side of the calcium and magnesium ledger for maintenance.
Chloride and phosphorus. Forage supplies meaningful chloride (more as the forage matures) and adequate phosphorus. Combined with intentional sodium supplementation, which brings additional chloride along with it, the chloride requirement is comfortably met without a separate intervention.
The picture across the macrominerals is consistent: forage is doing real work. A horse on adequate hay or pasture is meeting or exceeding the maintenance requirement for potassium, calcium, magnesium, and phosphorus, with chloride largely covered.
Where forage leaves gaps, and what a ration balancer is built to do
Forage leaves two reliable gaps, and they’re the reason ration balancers exist as a product category.
Trace minerals vary dramatically by region. Soil mineralization in the area where the hay was grown determines what trace minerals end up in the forage. Parts of the Pacific Northwest, Canada, and the upper Midwest have selenium-deficient soils, which means hay from those regions can run short on selenium. Many regions produce hay with high iron content that interferes with the absorption of copper and zinc. Iodine levels vary by proximity to coastal regions and by soil chemistry. The result is that copper, zinc, selenium, and iodine are commonly under-delivered by forage alone, and the deficiency pattern depends on where your hay comes from. A 2021 peer-reviewed feeding trial in Animals phrased the general principle plainly: roughages usually fulfil the requirements for macro minerals but not of trace elements of horses at maintenance.
Vitamin E is the other major gap. Fresh pasture is rich in vitamin E, but the vitamin is not heat-stable and degrades during the hay-curing and storage process. A peer-reviewed review by Finno and McKenzie (2025) in Veterinary Clinics of North America: Equine Practice documents that vitamin E losses approaching 50 percent occur in alfalfa hay stored for just one month, with continued losses during longer storage. A horse on a hay-only diet — particularly one eating hay that has been stored for several months — is reliably under-delivered on vitamin E.
A ration balancer is the engineered solution to both gaps. It’s a concentrated feed designed to be fed in small quantities, typically 1 to 2 pounds per day for an 1,100-pound horse, that supplies trace minerals, amino acids, and vitamins calibrated to NRC requirements, without adding significant calories. A ration balancer fed at the recommended rate closes those gaps without requiring an owner to test every batch of hay — though hay testing remains the gold standard for owners who can do it.
Two notes on ration balancers as a category, because the distinction matters. A ration balancer is not a complete feed; it’s a complement to forage. The whole product is formulated on the assumption that the horse is also eating adequate hay or pasture, and it doesn’t work as a stand-alone diet. A ration balancer is also not interchangeable with a vitamin-mineral supplement that comes in a 3-to-6-ounce daily scoop. The 1-to-2-pound serving size reflects a real density of macronutrients (especially amino acids and macromineral content) that smaller-scoop supplements typically don’t match.
The one macromineral forage cannot cover
This is the part of the package that has to come from somewhere else, intentionally, every single day, for nearly every horse.
A grass hay analysis typically returns less than 0.05% sodium — functionally zero. Forage essentially does not contain sodium in any meaningful amount. This makes sodium unique among the macrominerals: every other one is either supplied by forage at maintenance levels or formulated into the ration balancer as part of the trace mineral package. Sodium is the exception. It has to be added separately.
The fix is mechanically simple. One flat tablespoon of plain white loose salt weighs about two-thirds of an ounce (roughly 18 grams) and supplies approximately a quarter ounce of sodium (about 7 grams) and a third of an ounce of chloride (about 11 grams). Two tablespoons supplies about half an ounce of sodium, covering the maintenance requirement with comfortable margin, plus a meaningful share of the chloride requirement, with forage handling the balance.
This practice — top-dressing one to two tablespoons of plain iodized salt on the daily feed — meets both the sodium and iodine requirements established by the NRC for a maintenance horse. Iodized salt addresses both the sodium gap and the iodine trace-mineral gap that forage often leaves short in non-coastal regions.
Plain iodized salt, top-dressed on feed, is the most evidence-supported daily nutritional intervention in the entire equine literature for a maintenance horse. It is also the least expensive thing in the feed room.
The complete maintenance package, side by side
Putting it all together for an 1,100-pound horse at maintenance, on good-quality grass hay, fed appropriately. Amounts in ounces, with grams in parentheses for cross-reference to the underlying research:
| Mineral | NRC daily requirement | Forage (~22 lb grass hay) | Ration balancer (1–2 lb at recommended rate) | Iodized salt (1–2 Tbsp) | Total |
|---|---|---|---|---|---|
| Sodium | ~0.35 oz (10 g) | ~0 | ~0.07–0.25 oz (2–7 g) | ~0.25–0.5 oz (7–14 g) | Met with margin |
| Chloride | ~1.4 oz (40 g) | ~0.35–0.7 oz (10–20 g) | ~0.1–0.3 oz (3–8 g) | ~0.4–0.8 oz (11–22 g) | Met |
| Potassium | ~0.9 oz (25 g) | ~4–9 oz (120–250 g) | minor | — | Met many times over |
| Calcium | ~0.7 oz (20 g) | ~1–3.5 oz (30–100 g) | ~0.18–0.5 oz (5–15 g) | — | Met with margin |
| Magnesium | ~0.26 oz (7.5 g) | ~0.4–0.9 oz (10–25 g) | ~0.07–0.18 oz (2–5 g) | — | Met with margin |
| Phosphorus | ~0.5 oz (14 g) | ~0.5–1 oz (15–30 g) | ~0.1–0.35 oz (3–10 g) | — | Met |
| Trace minerals (Cu, Zn, Se, I) | varies | variable, often deficient | engineered to meet requirement | iodine from iodized salt | Met by balancer + iodized salt |
| Vitamin E | ~500 IU | low in cured hay | engineered to meet requirement | — | Met by balancer |
The package — adequate forage plus a ration balancer at the recommended rate plus one to two tablespoons of iodized salt — covers the published nutritional requirements for a maintenance horse. That’s not a controversial claim. It’s the NRC tables, read straight.
Above the foundation is a different conversation
Here’s the line the supplement aisle has not been careful about drawing.
The foundation — forage, ration balancer, iodized salt — is sufficient for maintenance. It is not sufficient for every horse in every situation, and nobody is saying it should be. There are real, evidence-supported reasons to add additional supplementation to horses’ diets, and those decisions are a legitimate and important part of horse ownership.
The rule above the foundation is different, though. Anything above the foundation should be answering a specific question. What am I solving for?
Electrolyte supplements are the cleanest example, and they live entirely above the foundation. They were never designed to be a daily maintenance product. They are formulated for specific situations: heavy sweat losses from endurance work, prolonged exercise in hot weather, multi-hour transport in summer conditions, clinical rehydration where the osmotic mechanics of an isotonic solution are being used as a therapeutic lever. Each of those is a different question with a different answer, and the right electrolyte for one is not necessarily the right electrolyte for another. The full research on this is the subject of the electrolytes piece in this series.
Hoof supplements answer the question: does my horse have a documented hoof problem that biotin or specific amino acids would help? Joint supplements answer the question: does my horse have age- or work-related joint changes that targeted ingredients have been shown to help? Gut and ulcer supplements answer the question: does my horse have a diagnosed or strongly suspected gastric issue? Hydration-focused water additives answer the question: is my horse drinking enough water, and would a palatability-driven intervention improve voluntary intake? Not every horse needs them. Some do.
And that’s the line. Foundation is foundation. Above that, name the need.
FAQ
My horse is on pasture instead of hay. Do I still need a ration balancer?
Likely yes, depending on your pasture quality and your region, but pasture changes the picture in meaningful ways. Fresh growing grass contributes things stored hay simply doesn’t:
- Water. Fresh pasture is roughly 70 to 85% water by weight, depending on species and maturity, which means a pasture horse is getting real hydration from forage that a hay-fed horse isn’t.
- Vitamin E. Fresh grass is the natural source. Finno and McKenzie (2025) in Veterinary Clinics of North America: Equine Practice document that vitamin E losses approaching 50 percent occur in alfalfa hay stored for just one month, with continued losses during longer storage. A horse on lush, fresh pasture may be meeting requirements directly; a hay-fed horse generally isn’t.
- Omega-3 fatty acids (specifically alpha-linolenic acid). Pasture grass is the horse’s natural source of ALA. Garton’s foundational 1960 work in Nature on the fatty acid composition of pasture grasses established that fresh grass contains substantial ALA, and subsequent peer-reviewed research has confirmed that the heat-sensitive unsaturated fatty acids degrade during haymaking and storage. This is the main reason omega-3 supplementation has become common practice for horses on hay-only diets, and is the basis for peer-reviewed research on omega-3 effects in horses such as Hess et al. (2013) in the Journal of Equine Veterinary Science.
- Vitamin A precursors (beta-carotene). The NRC Nutrient Requirements of Horses (6th rev. ed., 2007) documents substantial beta-carotene loss in stored hay compared to fresh grass, with the carotenoid pigment continuing to oxidize during storage.
What pasture doesn’t reliably change is the trace mineral picture. Soil mineralization where the grass grew still determines what’s in it, and pasture isn’t a free pass on copper, zinc, selenium, or iodine. A horse on rotational grazing across known-quality pasture may need less from a ration balancer than a horse on hay; a horse on overgrazed or poorly maintained pasture may need essentially the same support a hay-fed horse needs. When in doubt, the balancer covers the gaps.
Do I need to test my hay before I trust this?
Hay testing is the gold standard for knowing exactly what your horse is eating. If you can test, do. That said, modern horse-keeping doesn’t always make testing realistic. Most boarding barns, and many private owners, buy hay across the year from multiple sources — different farms, different cuttings, different species. Testing every batch isn’t feasible for most people, and waiting on lab results before feeding a new load isn’t either.
The numbers in this piece are averages drawn from the published forage analysis literature. They’re what the math looks like for a typical batch of grass hay grown under typical conditions. They’re not a substitute for testing your specific hay if you want certainty; they’re a way to make a reasonable decision when testing every load isn’t on the table. Perfect is the enemy of good. You’re doing the best you can with the information you have, and the averages are how we make that work.
My ration balancer already contains salt. Do I still need to add a tablespoon?
Read the tag. Most ration balancers include some salt — typically in the range of 0.5 to 1% of the feed by weight — but at a 1-to-2-pound daily serving, that contributes somewhere between about 2 and 7 grams of sodium to your horse’s day. The maintenance requirement is about 10 grams. Most balancers, even ones that prominently include salt, don’t get you all the way there at the recommended feeding rate. A tablespoon or two of plain iodized salt on top closes the gap. If you’re feeding a balancer significantly above the recommended rate (which most people aren’t), the math may shift.
My horse has a salt block in the pasture. Is that enough?
Probably not. Multi-year research at the Swedish University of Agricultural Sciences measured voluntary salt intake from individual blocks in Standardbred geldings during active training. The horses consumed an average of 14 to 19 grams of salt per day from the blocks — less than the maintenance requirement of about 25 grams, and intake didn’t increase to compensate after sweat-producing exercise. The authors concluded that voluntary block intake is not a reliable route to meet salt needs. A block is a fine free-choice option to have available, but for most horses it doesn’t close the sodium gap on its own. Loose salt top-dressed on the feed does.
What if my horse won’t eat salt on their feed?
A few practical angles. Start small — half a teaspoon for a few days, then a teaspoon, working up gradually so the change isn’t sudden. Mix the salt thoroughly into damp feed rather than sprinkling it on top, which helps with palatability. Some horses prefer fine-grain salt to coarse; others tolerate one brand and not another, so it’s worth experimenting if you hit resistance. Iodized table salt from the grocery store works as well as anything sold for horses, often for a fraction of the cost. If a horse persistently refuses salt on feed even after adjustment, a salt block remains the fallback — not ideal as a sole source, but better than nothing.
When would my horse actually need an electrolyte supplement?
Electrolyte supplements live above the foundation, and they answer specific questions: heavy sweat losses from endurance work or prolonged exercise, hot-weather competition, multi-hour summer transport, clinical rehydration where an isotonic solution is being used as a therapeutic lever. Each of those situations has real, evidence-supported reasons to add targeted electrolytes — and the right product for one situation isn’t necessarily the right product for another. The detailed walkthrough of what the research says about sweat composition, when supplementation helps, and when it doesn’t is the subject of the electrolytes piece coming next in the Why So Salty? series. The short answer: if your horse is at maintenance and isn’t sweating heavily, the foundation has them covered.
References
- National Research Council. (2007). Nutrient Requirements of Horses (6th rev. ed.). Washington, D.C.: The National Academies Press.
- Merck Veterinary Manual. Nutritional Requirements of Horses and Other Equids.
- Schubert, D.C., Neustädter, L.-T., Coenen, M., Visscher, C., & Kamphues, J. (2021). Investigations on the Effects of Different Calcium Supply Exceeding the Requirements on Mineral Serum Concentrations and Bone Metabolism in Young Warmblood Stallions. Animals, 11(8): 2439.
- Finno, C.J. & McKenzie, E.C. (2025). Vitamin E and Selenium-Related Manifestations of Muscle Disease. Veterinary Clinics of North America: Equine Practice.
- Garton, G.A. (1960). Fatty Acid Composition of the Lipids of Pasture Grasses. Nature, 187: 511–512.
- Hess, T.M., Rexford, J., Hansen, D.K., Ahrens, N.S., Harris, M., Engle, T., Ross, T., & Allen, K.G. (2013). Effects of Ω-3 (n-3) fatty acid supplementation on insulin sensitivity in horses. Journal of Equine Veterinary Science, 33: 446–453.
- Jansson, A. & Dahlborn, K. (1999). Effects of feeding frequency and voluntary salt intake on fluid and electrolyte regulation in athletic horses. Journal of Applied Physiology, 86(5): 1610–1616.
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