Nutrients, clearly explained
Tap any nutrient to read what it does in the horse, why it matters, when it becomes critical and how much a horse needs.
Macrominerals
Calcium
What it does in the horse
Some 99 per cent of a horse's calcium is bound in the skeleton — roughly seven kilograms in an average-sized animal. What little circulates handles jobs that cannot wait: contracting muscle, carrying nerve signals, clotting blood. That circulating level is held steady at all times, and bone serves as the reserve it is drawn from.
Why it matters
A ration that supplies enough calcium month after month keeps the bone depot filled instead of drawing it down. That is the difference between a skeleton that carries reliably and one that quietly compensates for the feeding.
When it becomes critical
Calcium cannot be judged on its own. If the ration permanently provides little calcium or a lot of phosphorus, the ratio shifts at the expense of bone. The frame: at least as much calcium as phosphorus, at most three times as much. A moderate calcium surplus, by contrast, is uncritical.
How much a horse needs
Maintenance: about 12 g daily at 300 kg body weight up to around 20 g at 600 kg. Work barely changes this; the requirement is markedly higher for pregnant and lactating mares and during growth.
Phosphorus
What it does in the horse
About 80 per cent of phosphorus is bound in the skeleton together with calcium, giving it hardness. The rest works in metabolism: phosphorus is part of ATP, the energy carrier every cell pays its work with, and supports the microbes in the hindgut in digesting fibre.
Why it matters
A ration with a fitting phosphorus share supplies two systems at once — bone substance and energy production in the cell. Neither draws attention as long as both are right.
When it becomes critical
It is the proportion, not the quantity, that decides. Plenty of grain means plenty of phosphorus; let it stay dominant for weeks and less calcium is absorbed, with bone making up the difference. The same span applies as for calcium — phosphorus never above calcium, calcium at most triple the share.
How much a horse needs
Maintenance: about 8 g daily at 300 kg up to 14 g at 600 kg — always slightly below the calcium figure. Growth, pregnancy and lactation raise the requirement.
Magnesium
What it does in the horse
Magnesium acts as a helper in a large number of enzymatic reactions and is involved in signal transmission between nerve and muscle. It is stored mainly in bone and muscle.
Why it matters
A ration sufficiently supplied with magnesium supports exactly those processes that go unnoticed as long as they work — muscle activity and nerve conduction. They usually become noticeable only when something is missing.
When it becomes critical
Genuine undersupply is rare and most likely on intensively fertilised, species-poor pasture grass. What is then observed is over-excitability, muscle tremor and tension up to cramping. A healthy horse tolerates surpluses well; caution applies only when magnesium AND phosphorus are both supplied generously — that combination raises the risk of urinary sand.
How much a horse needs
Maintenance is quoted as 53 mg per kilogram of metabolic body mass per day (kg BW^0.75); in everyday terms roughly 4 g daily at 300 kg and 6 g at 600 kg. Work adds a little, lactation and growth a good deal more.
Sodium
What it does in the horse
Sodium distributes water between the cells and the space around them, is involved in muscle and nerve function, and governs when a horse feels thirst at all.
Why it matters
Forage leaves exactly one mineral gap open, and this is it. Where salt is reliably on offer, water intake stays up and circulation and muscle work keep their footing — which matters most in warm weather and after sweating.
When it becomes critical
With a short supply, water intake falls, fatigue sets in earlier, and circulation and performance may give way. Sweat causes substantial additional losses. A freely accessible salt lick covers this simply. An excess is unproblematic in healthy horses with free access to water.
How much a horse needs
Strictly speaking only 2–3 g a day are needed; recommendations add a safety margin and land near 13 g for a 300 kg horse and 23 g for a 600 kg one, rising clearly once sweating starts. Offered salt freely, most horses meter it themselves.
Chloride
What it does in the horse
In the ration, chloride almost always appears together with sodium — the two form common salt. Together they regulate fluid distribution and acid-base balance; chloride additionally supplies the building block for gastric acid.
Why it matters
If the ration's salt supply is right, chloride is covered automatically. It is therefore the nutrient that needs the least separate attention — as long as sodium is right.
When it becomes critical
The relevant losses run through sweat. With long, heavy sweating and no replacement, chloride balance can tip; a salt lick catches this.
How much a horse needs
Maintenance: about 17 g daily at 300 kg up to 29 g at 600 kg — in practice covered together with sodium via common salt.
Potassium
What it does in the horse
Potassium is the bulk mineral inside the cell and forms, with sodium, the pair through which every cell regulates its electrical balance. Nerve conduction and muscle contraction depend on it.
Why it matters
Because grass and hay naturally contain plenty of potassium, this item is practically always met in a forage-based ration. It still matters — it belongs to the values you check in order to tick them off.
When it becomes critical
Undersupply is hardly to be expected with usual feeding. Losses only become relevant under very high workload with heavy sweating. A healthy horse excretes surpluses without trouble.
How much a horse needs
Maintenance: about 15 g daily at 300 kg up to 25 g at 600 kg — as a rule easily covered by hay and grass.
Sulphur
What it does in the horse
Sulphur reaches the horse almost exclusively as part of amino acids. Methionine and cystine build, among other things, keratin — the structural protein of hoof horn, hair and skin.
Why it matters
Anyone who keeps an eye on the ration's protein supply covers sulphur automatically. A separate sulphur item in ration calculation is therefore unnecessary.
When it becomes critical
An isolated sulphur deficiency plays no practical role as long as protein and amino acids are right. Targeted sulphur supplementation beyond the usual feed is normally not required.
How much a horse needs
No daily reference figure is published for sulphur on its own. Cover is assumed once the ration carries enough protein — and with it methionine and cystine.
Trace elements
Iron
What it does in the horse
Iron binds oxygen and releases it where work is being done. Roughly four fifths of the store circulates in blood, the remainder sits in muscle pigment and in reserves. Without this trace element there would be no oxygen transport at all.
Why it matters
A ration with sufficient iron keeps blood formation running. The real checkpoint, though, is a different one: almost every basic feed already supplies enough — so the question is whether a supplement is stacking on top unnecessarily.
When it becomes critical
With iron the risk sits at the top end, not the bottom. Uptake is tightly throttled in the gut, and shortage arises practically only in foals or after blood loss. Generously supplemented amounts bring no benefit and burden the liver over time.
How much a horse needs
Maintenance works out at 420 mg a day for a 500 kg horse, which everyday feed supplies without help. Anything above 1000 mg per kilogram of dry matter counts as the ceiling.
Zinc
What it does in the horse
Zinc participates in a large number of enzymes, above all where tissue is constantly renewed: skin, mucous membranes, coat and hoof horn. Immune defence draws on it too.
Why it matters
Everything that regrows on a horse depends on this supply. Because hay and grass regularly fall short here, zinc is one of the few items where the calculation almost always pays off.
When it becomes critical
It gets tight from two directions: the basic feed often supplies too little, and a lot of grain or calcium in the same ration further slows uptake. Undersupply shows as scaly, crusty skin, hair loss and frequent infections. Towards the top the margin is wide — surpluses are unproblematic.
How much a horse needs
Maintenance: 423 mg daily at 500 kg, equivalent to 30–40 mg per kg of feed dry matter. Since forage rarely manages that alone, zinc is part of nearly every supplement.
Copper
What it does in the horse
Copper is required when blood is formed, pigment is deposited or connective tissue is built. Firm horn, load-bearing tendons and ligaments and an orderly bone metabolism all depend on it.
Why it matters
Wherever tissue has to be firm and elastic at once, copper is involved. In rations for pregnant mares and growing horses this item pays into structures that are meant to last for years.
When it becomes critical
Forage often brings little copper along, which is why breeding-mare and foal rations in particular stay below requirement. Undersupply can show as a lightened coat and as problems in connective tissue and skeleton. Copper is well tolerated; only permanently very high doses burden the liver.
How much a horse needs
Maintenance amounts to about 106 mg a day for a 500 kg horse; measured against dry matter that is 8–10 mg in every kilogram. Where a mare is carrying or a youngster is growing, plan at the upper end.
Manganese
What it does in the horse
Manganese acts as a helper to numerous enzymes involved in mineral and fat metabolism and is needed when cartilage is built — that is, where joints are meant to stay resilient. Immune defence uses it too.
Why it matters
In a normal ration this item is quietly met. It still belongs in the calculation — what gets checked is not only what is missing, but also what is already covered.
When it becomes critical
Undersupply is barely described in horses. The other end is more noticeable: very high manganese contents in green forage can interfere with iron uptake and thereby favour anaemia.
How much a horse needs
Maintenance comes to 420 mg a day for a 500 kg horse, or roughly 40 mg in every kilogram of dry matter — a level basic forage normally reaches on its own.
Selenium
What it does in the horse
Selenium belongs to the body's defence against oxidative damage: together with vitamin E it keeps cell membranes safe from attack by aggressive breakdown products. The two complement each other; neither replaces the other.
Why it matters
For no other item in the ration does precise calculation matter this much. Selenium is the nutrient where an analysis makes the biggest difference — supplementing by feel quickly becomes risky here.
When it becomes critical
Both directions carry risk. Where soils are poor, defence and muscle tissue pay the price — in foals as far as white muscle disease. Yet the safe corridor upwards is unusually tight: poisoning becomes a real prospect from roughly 2 mg per kilogram of dry matter onwards. Dosing selenium therefore belongs on measured ground, not on estimates.
How much a horse needs
Maintenance: 1.1 mg daily at 500 kg, equivalent to 0.1–0.2 mg per kg of feed dry matter. Between undersupply and overdose there is less room here than with any other nutrient.
Iodine
What it does in the horse
From iodine the thyroid builds its hormones, and those hormones help set the pace at which metabolism works. Only tiny amounts are needed — but reliably.
Why it matters
A few milligrams decide over a control loop that affects the entire body. In ration calculation, iodine is therefore an item you do not estimate but compute.
When it becomes critical
Unusual about this nutrient: too little and too much lead to the same picture, an enlarged thyroid. Seaweed preparations in particular often carry unexpectedly high amounts and slip unnoticed into excess. What is called for is the sparingly measured, correct amount.
How much a horse needs
Maintenance: around 1.6 mg daily at 500 kg, equivalent to 0.2 mg per kg of feed dry matter. With an upper limit of 4 mg per kg of feed, little room remains.
Cobalt
What it does in the horse
Cobalt does not act directly but as a component of vitamin B12. The microbes in the gut build this vitamin from the cobalt in the feed, and it is needed for blood formation and nerve function.
Why it matters
In practice this item takes care of itself as long as the gut flora is working and the ration is normally composed. It appears in the calculation so that it can be ticked off.
When it becomes critical
With usual feeding, cobalt is covered; genuine undersupply is not described in horses. It can at most get tight on very poor sandy and weathered soils.
How much a horse needs
There is no figure for a daily amount of cobalt. Orientation comes from the feed itself: roughly 0.1 mg in each kilogram of dry matter is regarded as safe.
Vitamins
Vitamin A (with β-carotene)
What it does in the horse
Vitamin A is needed for skin and mucous membranes, for vision and for immune defence. It does not enter the horse as a finished vitamin but as β-carotene from green plant material — the body builds it from there.
Why it matters
Mucous membranes are the first border against pathogens, and their renewal depends on this vitamin. As long as fresh green is on the menu, the ration covers this item by itself.
When it becomes critical
The stable months are the critical stretch: stored hay loses much of its β-carotene, so a gap can open across weeks — showing up as brittle horn, dry membranes and infections that come more often. In the other direction, finished vitamin A turns toxic at high doses; as a standing dose, 1000 IU per kilogram of body weight per day marks the ceiling. With pure β-carotene that risk does not arise.
How much a horse needs
Maintenance: about 15,900 IU a day for a 500 kg horse; for breeding mares and foals the figure is considerably higher. Where pure β-carotene is given, breeding mares receive at least 200 mg daily.
Vitamin D
What it does in the horse
Vitamin D governs how much calcium and phosphorus are taken up from the feed and deposited in the skeleton. Unlike most nutrients, the ration is only one of two sources here: in daylight the skin produces the vitamin itself.
Why it matters
Without vitamin D even the best calcium content in a ration achieves little — it is the link between feed and bone. In horses, though, its role in calcium balance is smaller than in other species.
When it becomes critical
Undersupply is barely described in horses that see daylight. The risk clearly sits at the top end: horses react sensitively to overdosing, up to calcium deposits in vessels and organs. Anyone combining several vitaminised compound feeds should keep an eye on the total.
How much a horse needs
Maintenance: about 3,200 IU a day for a 500 kg horse — little compared with other vitamins. With supplementation, restraint is the better direction.
Vitamin E
What it does in the horse
Vitamin E intercepts aggressive oxygen compounds before they attack cell membranes — particularly in heart and skeletal muscle. Selenium does the same job elsewhere; together the two form the antioxidant shield.
Why it matters
The more muscular work a ration has to accompany, the more this item counts. In sport horses vitamin E belongs to the values you plan deliberately rather than hope for.
When it becomes critical
Fresh pasture grass brings plenty along, long-stored hay and old oats little — so in a stable winter the ration can slip below requirement. It becomes visible in the musculature (in foals, together with selenium deficiency, as white muscle disease). Towards the top vitamin E is good-natured; drawbacks appear only at extreme amounts.
How much a horse needs
Maintenance: about 530 mg a day for a 500 kg horse. Where muscles are heavily worked or problems exist, the requirement lies clearly above that.
Vitamin K
What it does in the horse
Vitamin K makes blood clotting possible and also plays a part in bone metabolism. The larger share is generated by the gut flora, so the ration usually only tops it up.
Why it matters
That blood clots after an injury is vital — and with an intact gut it is assured without help from the feeding. In ration calculation this is an item you check and tick off.
When it becomes critical
It only becomes critical in two situations: when the gut flora is damaged — through diarrhoea or certain medications — or when spoiled feed brings antagonists along. Regular dosing is not indicated in healthy horses. No toxicity limit is known for vitamin K taken in through feed in horses; menadione — a synthetically produced form of this vitamin — is dangerous only as an injection, and that is a decision for the vet.
How much a horse needs
The tables give no daily figure here. A level of 0.5 mg in each kilogram of dry matter counts as comfortably sufficient, and in practice the gut covers it anyway.
Vitamin B1
What it does in the horse
Thiamine, as vitamin B1 is also called, stands at the beginning of energy production from carbohydrates and is at the same time required for orderly nerve function.
Why it matters
The requirement grows with the carbohydrate share of the ration — the more starch and sugar, the more B1. With plenty of forage, feed and gut flora supply this item together.
When it becomes critical
It gets tight with very concentrate-heavy, fibre-poor rations and through substances that destroy B1 — found in mould, marsh horsetail and bracken. Signs of a gap are skittishness, uncoordinated movement and declining performance. A surplus via feed is harmless.
How much a horse needs
Maintenance is reckoned at 32 mg daily for 500 kg of live weight, which corresponds to 3–5 mg in each kilogram of dry matter. Heavy workloads sit at the upper end.
Vitamin B2
What it does in the horse
Riboflavin — vitamin B2 — takes part in the reactions that release energy and is likewise needed when fat and protein building blocks are converted.
Why it matters
In an ordinary ration this item fulfils itself. It appears in the calculation so that it can be ticked off as checked rather than forgotten.
When it becomes critical
Undersupply has so far only been produced under experimental conditions; in everyday stable life it plays no role. More than needed via feed is harmless.
How much a horse needs
Maintenance: about 21 mg a day for a 500 kg horse, equivalent to around 2 mg per kg of feed dry matter.
Vitamin B6
What it does in the horse
Pyridoxine — vitamin B6 — accompanies the conversion of amino acids and makes the protein from the feed usable for the body.
Why it matters
Because gut flora and basic feed carry this requirement together, B6 does not show up as a problem area in a normal ration calculation.
When it becomes critical
A stand-alone undersupply is rare in horses. It is conceivable with a disturbed gut flora or with very one-sidedly composed rations.
How much a horse needs
No separate daily reference value is defined for horses. Supply is considered covered through production in the gut and through the feed.
Vitamin B12
What it does in the horse
Cobalamin — vitamin B12 — is needed wherever cells divide, above all in blood formation, and for healthy nerve function. It is the only vitamin with cobalt at its centre.
Why it matters
In the ration it is less the vitamin itself that counts than the cobalt the gut builds it from. Keep an eye on that raw material and the rest takes care of itself.
When it becomes critical
As long as the gut is working, an extra dose is superfluous — even low feed contents scarcely ever produced a deficiency. In severely emaciated or anaemic horses a dose can support blood formation.
How much a horse needs
There is no fixed daily amount for the horse. With usual feeding and sufficient cobalt, production in the gut carries the supply.
Vitamin C
What it does in the horse
Ascorbic acid — vitamin C — protects cells against oxidative wear. In the horse the liver takes over production, so the feed does not have to fulfil that task.
Why it matters
This is precisely where equine and human nutrition part ways: what we need on the plate daily, the horse generates itself. Supplementation is the exception, not the rule.
When it becomes critical
In a healthy horse the question of a gap does not arise. In particular strain or illness situations — respiratory problems, for instance — a dose can make sense.
How much a horse needs
No daily requirement via the feed is defined, because the horse forms vitamin C itself.
Biotin (vitamin H)
What it does in the horse
Biotin is part of the B group and is needed when keratin is formed — the structural protein that hoof horn, skin and coat are made of. Part of the supply comes from production in the gut.
Why it matters
It is the item horse owners most likely know from the label. Important to note: horn grows slowly, so a good supply pays off over months, not weeks.
When it becomes critical
If the gut flora is disturbed, the self-produced share falls. With poor, brittle hoof horn, biotin is therefore supplemented deliberately — visible change takes months, though, because only newly growing horn benefits.
How much a horse needs
Maintenance: about 3 mg a day for a 500 kg horse. To support hoof horn specifically, higher amounts are often used in practice.