Liposoluble vitamins (present and soluble in fats), whose needs seem to be more or less well defined, must be discriminated from hydro soluble vitamins (soluble in water), [which] requirements remain hypothetic.

Most vitamins must be given by feeding, as the horse is not able to synthesi[s]ze, to develop the vitamins in its organism (except vitamin B, C and D).

Vitamins are indispensable for the maintenance of the organism, growth and reproduction.
All vitamins are brought through feeding, as far as it is fresh, good-quality and in required quantity.

Ageing, stress, preparation for competition, daily work, illness, antibiotics, inflammation, and food shortage are all factors which can lead to a lack of vitamins (e.g. B and K) produced by the intestinal flora. This is what is called avitaminosis.

However, hypervitaminosis can also be dangerous and lead to metabolism troubles. But it is of little effect to administer vitamins without adding the nutritive elements (i.e. minerals and amino acids) they control and which make them efficient. As an example, vitamin D works with calcium and phosphorus, vitamin H works with zinc.

It is therefore highly recommended to carefully manage the daily allowance in order to make it complete and well-balanced.

Vitamine AIt exists in its natural state in the form for provitamin A (the precursor of vitamin A) in wheat and carrots. This provitamin A (mainly carotene) is transformed in vitamin A by the bacteria of the digestive tract and the liver, where it is partly stored.
Green fodder, alfalfa meal (lucerne), grass silage are an outstanding source of vitamin A. However, it deteriorates about 10% per month. It is quickly deteriorated with the hay yellowing, and the horse makes bad use of the carotene contained in the graminicides.

Vitamin A plays an important role in digestion and absorption of sodium, calcium, phosphorus and nitrogen.

It is associated with zinc in the synthesis of proteins and the protection of epitheliums (e.g. skin, pulmonary, vascular, and glandular epitheliums) as well as with vitamin D, whose effect is reinforced. The intake of vitamin A must be 5 to 10 times higher than that of vitamin D. Vitamin A also stimulates heats, ovulation and nesting. The deficiencies are mainly encountered in winter (February – March) when the glycogen reserves are low and the fodder concentration is the lowest. On the other hand, in summer time, when the weather is warm, sunny and dry, the concentration of vitamin A in the fodder can be insufficient, as vitamin A is thermolabile, it badly resists heat. In these conditions, a supplementation is therefore recommended.

Vitamin A also plays an important role in vision and the metabolism of sexual hormones through the thyroid gland.
In foals, during gestation, it doesn’t go through the placenta barrier but remain in the colostrum.

The quantity of vitamin A is expressed in I.U. (International Units).
1 mg of vitamin A = 3333 IU.

The RDA (recommended daily allowance) is 15 mg (50,000 I.U.) per 500 kilos. 40 to 50,000 extra units are recommended for mares in winter as well as during the lactation period.


The maximal RDA of vitamin A is 20000 to 30000 IU per kilo. An excess may cause bone fragility, a lack of vitamin E and coagulation troubles.

Positive interactions:

Vitamin A improves bioavailability of vitamin E, phosphorus and choline. It facilitates absorption of calcium and zinc, allows the mobilization of iron resources, and promotes the use of vitamin D.

vitamines BVitamins B form a group of 8 vitamins which play an important role in the cellular metabolism.
They can be found in their natural state in fruits, beer yeast, cereal germs and milk.
They have multiple roles, but they are all involved in various growth factors. They are not stored by the organism, except B3 and B12 in very small quantities. It is therefore imperative for the horse to be offered a daily intake.

Positive interactions:

Vitamins from group B potentiate the bioavailability of all vitamin B, vitamin E, chlorine and sulphur. They are needed for the absorption of iron and the growth of the gut flora. They also prevent the reserves of vitamin A from depleting.


Vitamin B1 promotes the liberation of energy as it is needed to transform sugar (carbohydrate), help the nervous system work well (disposal of wastes), and favour muscular contraction.
Associated with vitamin B12, it produces a calming effect.

Together with vitamin C it plays a preventive role against myoglobinuria. Myoglobinuria usually happens on a horse suddenly put back to work after a day or more of rest in the stable, while its feed ration has not been adapted. This affection hits the muscular cells, the latter burst out and release myoglobin (a toxin) into the blood. The muscles get painful and contracted. Those of the back and the rump are the most affected. By palpating them one can feel they are hard and very touch-sensitive.

Daily allowance:

The RDA (recommended daily allowance) is 50 to 100 mg / 500 kilos.


Deficiency in vitamin B1 manifest itself through fatigue, loss of hunger and weight, constipation, dull coat, and circulatory, nervous and cardiac trouble.


Non-toxic vitamin at high-dosage.

Vitamin B2 is involved in the production of energy and the metabolism of proteins and lipids. As much as vitamin A, it acts on vision and on the health of the skin and mucosae.
It activates vitamins B6 and B9. It is also involved in regulating the body temperature by increasing the resistance of the organism to cold. It can also prevent conjunctivitis from occurring.

Daily allowance:

The RDA (recommended daily allowance) is 50 to 100 mg / 500 kilos.


Deficiency in vitamin B2 leads to eye, skin and gastro-intestinal illness (digestive ulcers). Deficiency also causes inflammatory reactions of the lips and the tongue. Anorexia is sometimes noted as well as absence of heat (anoestrus).


Vitamin B2 is non-toxic at high-dosage.

Vitamine B3

Vitamin B3 is involved in the synthesis of sexual hormones, the metabolism of carbohydrates, proteins and lipids as well as in the production of red blood cells.

It is also called vitamin PP (pellagra preventive), as a deficiency of this vitamin causes pellagra. Pellagra is characterized by dermatitis (skin disease), diarrhoea, and in the worst cases dementias which can lead to death if they remain untreated (i.e. without intake of vitamin B3).

Niacin is one of the most stable vitamins. It is resistant to heat, light, moisture, acids and bases, as well as oxidizing agents.

Daily allowance:

The RDA (recommended daily allowance) is between 50 and 100 mg / 500 kilos.
The increase in protein contents goes along with that of niacin and leucine. An excess of tryptophan reduces the need of niacin.
The horse seems to require less niacin than most of the other animal species.


Skin, neurological, digestive and blood disorders. Cessation of growth, immune weakness, rhinitis.


Non-toxic vitamin, even with high dosage.

The intake of high dosage of niacin (higher than 350 mg per kilo of body weight, i.e. 175000 mg/500 kilos) has highlighted a wide range of important effects such as an increase of the cardiac rhythm and breathing speed with respiratory paralysis, saturation of fats in the liver, cessation of growth and even death in the most extreme cases.
This dosage is obviously far from the one encountered in the food rations. Any excess of niacin is quickly excreted: 1/3rd of the dosage within 24 hours.

Positive interactions:

Vitamin B3 improves bioavailability of proline.

Vitamine B5

Vitamin B5 is involved in the synthesis of hormones and neurotransmitters, nervous transmission, production of red blood cells, division of cells, as well as production of energy.
It is a metabolic precursor of coenzyme A, which is essential to the synthesis and metabolism of proteins, carbohydrates and lipids. It is found in quite concentrated ratios in germs and wholegrain cereals as well as in varieties of stinging nettles. Of the known natural products, royal jelly is the richest in vitamin B5.

Folic acid (vitamin B9) and biotin (vitamin H) are both needed for vitamin B5 to be efficient. Vitamin B5 and biotin work on the metabolism of niacin (vitamin B3). It must be highlighted that vitamin B5 deficiency can be partially compensated by ascorbic acid (vitamin C).

Daily allowance:

The RDA (recommended daily allowance) is between 50 and 100 mg / 500 kilos.


The first symptoms noticed in case of deficiency are identical to those referred to with other vitamins B: loss of appetite and cessation of growth.
The reproductive function may also be weakened. Regarding the nervous aspect, unstable movements are noticed. Digestive trouble with ulceration and diarrhoea may occur.

La fonction reproductrice peut être également affaiblie. Sur un plan nerveux, on enregistre des mouvements instables. Des perturbations digestives avec ulcération et diarrhée peuvent survenir.


Although small quantities of this vitamin are stored in the heart, liver and kidneys, any excess is quickly excreted. No case of apparent toxicity has been mentioned, neither in the animal nor the human body, even after huge dosage of pantothenic acid being administered (1 g/ kg of body weight, i.e. 500 g / 500 kilos).

vitamine b6

Vitamin B6 favours the metabolism of proteins and plays an essential role in the enzymatic system. It favours the normal development of embryos and contributes to the renewal of red blood cells. It plays an important role in the synthesis of adrenalin and fights muscle fatigue.

The micro organisms in the horse caecum (first part of the colon) synthesize pyridoxine, the precursor of vitamin B6, although it is not completely resorbed in blood like the other vitamins B are. Horses must therefore find vitamin B6in their daily ration. Besides, this bio molecule doesn’t accumulate and is eliminated within 48 hours following resorption.

Daily allowance:

The RDA (recommended daily allowance) is 50 mg / 500 kilos.


Vitamin B6 is involved in many metabolic functions. A deficiency may cause major metabolic malfunctions.

The symptoms are non-specific and look like those noticed with other vitamins B: loss of appetite, diarrhoea, slowdown in growth, weariness, lethargy, loss of immune defences, dermites, abscesses, ulcers.
Blood cell abnormalities are also noticed.

Positive interactions:

Vitamin B6 increases bioavailability of magnesium, potassium and tyrosine. Besides, it is needed for the metabolism of zinc and alanine and favours absorption of lysine.


Excess of dosage has no effect.

Any excess of vitamin B6 is directly eliminated.
Convulsions could only occur if largely exceeding dosage (over 4 g/kg of body weight, i.e. 2 kilos of vitamin B6 / 500 Kg) were administered.

Vitamine B8(Vitamin B7 in anglo-saxon countries)

Biotin is a coenzyme involved in the metabolism of fat acids, carbohydrates and amino acids, as well as biosynthesis of vitamins B9 and B12.

Biotin is a highly stable vitamin.

Bioavailability of biotin in cereal –based products is poor, if not inexistent. Corn , soya flour and dried yeasts (brewer’s yeasts) are an exception to this trend, as biotin is entirely bio available in them.

Most publications dealing with horse requirements in vitamins state that biotin supplements are not necessary. Over the last 30 years, research has caused confusion by highlighting the positive role of biotin in preventing and curing damaged hooves.
These lesions do not only depend on a deficiency in biotin; it is known that important quantities of vitamins, amino acids (sulphur), minerals (zinc) and proteins are needed to harden the horn of the horse’s hoof. Biotin alone or complemented with zinc is not sufficient.
Besides, given the time needed for keratin to regenerate, the first visible results are often noted after several months.
Although the optimal dosage of biotin for a grown-up horse (500 kilos) is about 1 to 2 mg/day, quantities between 15 and 30 mg/day have to be administered for 6 to 10 months when healing the hoof.
It has also been highlighted that doubling the daily dosage (i.e. 2 to 4 mg) may cause some “excitement” of the horse. This hyperactivity can nevertheless be corrected by adequate supplement of vitamin B12.

Daily allowance:

The RDA (recommended daily allowance) is 2 mg / 500 kilos.


The first symptoms noticed in case of deficiency in biotin are a dry and scaly skin, mangy dermatitis and a softening of the hard tissues (like the horn of the hoof).
A more severe deficiency drastically affects the blood sugar levels, leading therefore to hypoglycemia and even to death on younger animals.


Biotin has no toxicity at all for the horse, even in high dosage. However, biotin dosage higher than 100mg/day may affect the young foal’s growth. Grown-up animals tolerate more than 1g/day without any negative effect, thanks to the low capacity of storage and the efficient renal function.

Positive interactions:

It fosters production of vitamins B9 and B12.

Vitamine B9

Vitamin B9 is involved in hematopoiesis (i.e. production of red blood cells) as well as in the synthesis and action of some amino acids. It also acts as a precursor of a coenzyme directly involved in the fabrication of genetic material (DNA – RNA). A small quantity of folic acid is necessary for the healthy functioning of the metabolic activities. The efficient concentration depends on the levels of vitamin B12, iron, but also methionine and choline (two essential amine acids).
The lower the levels of methionine are, the more important the needs in vitamin B9 will be.

The horses staying in stables have lower rates of vitamin B9 than those staying in pasture.
Vitamin B9 can be found in green-leaf vegetables, including grasses. Aliments rich in animal proteins and cakes with extracts of seed oil contain the largest quantities of folic acid.
An intensive work, over a period of six months, makes the levels of vitamin B9 fall. Horses with lover levels encounter more difficulties to reach the same level of endurance and performance than the others. As folic acid has very low capacity of resorption, it must be compensated by an important daily dosage. A horse in a stable could then have similar rates of vitamin B9 to those of animals in pasture.

Positive interactions:

Folic acid improves bioavailability of iron

Daily allowance:

The RDA (recommended daily allowance) is 50 to 100 mg / 500 kilos.


A deficiency in folic acid mainly leads to anaemia (deficiency of red blood cells) which is characterized the latter being of a larger size (macrocytic anaemia).
The fall of circulating rates of vitamin B9 makes non specific symptoms appear, such as general weakness, loss of appetite, diarrhoea, and an increased sensitivity to infectious agents.


If vitamin B9 can be assimilated by organs like liver, kidneys or even muscles, any excess is quickly eliminated.
No harmful effects to the horse have been noticed in case of over dosage of this vitamin.

vitamine B12

Vitamin B12 fulfils the action of vitamins B9 and B8 and its activity is related to cobalt during the synthesis of proteins and to the maintenance of the haemoglobin level (red blood cells) in blood.

This vitamin is also involved in growth, tonus and fight against allergies.
Since it is involved in the fixation of iron, it is highly recommended for anaemic horses (lack of red blood cells). Synthesized by bacteria in the intestinal tract, it is also involved in the development of some amino acids, including methionine.

Vitamin B12 has a calming effect on brazen or simply excited horses. This hyperactive state can sometimes be associated with an excess of biotine. In such a case, administrating 1 mg of vitamin B12 on a daily basis will serve as an antidote and correct the situation.
Plants contain no or very little vitamin B12.
When using a complete feeding, whose level of cellulose is lower than 10%, an extra source of vitamins will be needed.

Daily allowance:

The RDA (recommended daily allowance) varies with the levels of methionine, choline, folic acid, thiamine and biotine.
The needs will also vary with the age and effort.
The RDA is 800 to 1200 mg / 500 kilos.


Deficiencies in vitamins B12 lead to a diminution of appetite, anaemia, as well as a downgrade of the overall state of the horse, atrophy of the spleen or the adrenal glands, and a decrease of immunity.


No toxicity or annoying side effect is known, even with high dosage.

Positive interactions:

Vitamin B12 is involved in the metabolism of iron.


Vitamin C is found in its natural state in plants containing chlorophyll, fruits and milk.

It regulates cell breathing and hormonal secretions (mainly of the adrenal cortex and pituitary).

At high dosage, it is involved in myoglobinuria (presence of myoglobin[e] in the urine due to a muscular sickness), dead beat, heat strokes and overwork.

Very young foals produce too little vitamin C. They will be immediately given a nutritional supplement if they are fed artificially (2 mg per ml of milk or milk substitute). On the other hand, milk from breeding mares contains sufficient quantities of ascorbic acid.

Performing horses, when active, also have a great need of vitamin C.

Vitamin C plays a critical role in the formation and maintenance of the skeletal tissues. It also has a stimulating effect on immune defence mechanisms. Vitamin C also ensures an important mission of carrying iron from plasma to storage areas.

Daily allowance:

The RDA (recommended daily allowance) is 1 to 1.5 g / 500 kilos on high-performing horses, and 0.5 g / 500 kilos on breeding mares and stallions.


Its deficiency is called scurvy. This sickness is characterized by bleeding and swollen gums, together with an extremely weak condition and painful bones.
Although they are able to bio synthesize vitamin C, horses can suffer the effects of a deficiency in ascorbic acid. It is the case with older or overloaded horses. Vitamin C is also recommended on feverish or recovering horses.


No toxicity or annoying side effect is known, even with high dosage. The theory goes that high dosage may cause the appearance of kidney stones, but this has never been noted on the horse.

Positive interactions:

Vitamin C potentiates the effects of vitamins from complex B, vitamin E, magnesium, selenium and proline. It protects vitamins from complex B against oxidation and helps prevent toxicity of vitamin D. Besides, it improves the efficiency of cysteine and increases the absorption of iron, zinc and calcium. Finally, it is needed for the synthesis of carnitine.

Vit D

Vitamin D is available in two forms: D2 (ergolaciferol), vegetal-based (fodder, sun-dried hay) and D3 (cholecalciferol).

Vitamin D3 is made from cholesterol by the organism when exposed to sunlight (UV rays), although it is also found in food (e.g. milk, cod liver oil, eggs, wild mushrooms).

Vitamin D is the source of a hormone (calcitriol) which plays a fundamental role in calcification (binding of calcium by the organism – robustness of the bones). Together with vitamin K2, it helps calcium and phosphorus resorption in the intestine. Vitamin D also commands the expression of over 200 genes.

Daily allowance:

The quantity of vitamin D is expressed in I.U. (International Units).
1 mg of vitamin A = 40.000 IU.
The RDA (recommended daily allowance) is between 5 and 10,000 IU / 500 kilos. It may go up to 60,000 IU for high performing horses.


A lack in vitamin D causes rickets in young horses (insufficient calcification of the bones and cartilage). This is what is called vitamin D deficiency rickets.


Note that an excess of vitamin D (much more common than a deficiency) worsens bone lesions and soft tissue calcification (large vessels, heart valves, lungs, kidneys), which leads to cardiac rhythm disorders (tachycardia, intolerance to exertion) and excessive thirst.

Positive interactions:

Vitamin D stimulates the intestinal absorption of calcium, magnesium, phosphorus and vitamin K. Besides, it enhances the use of vitamin A.

Vitamine E

Vitamin E gathers together a group of 8 biological molecules. Together with selenium, they mainly act as an antioxidant agent against the reactive oxygen species produced by the degradation of lipids (fat acids). Vitamins E are then regenerated by vitamin C, glutathione (a compound made of 3 animate acids which play an important role as cell protection) and coenzyme Q10 (also called ubiquinone 10) which is a basic compound of cellular breathing.
It therefore protects the organism as much as vitamins A and C.

Vitamin E is also involved in the growth of the foal, muscular work (energetic mechanism), sugar metabolism (carbohydrates), foetus growth, and sexual cells development.
Its role is truly beneficial for the cellular breathing of the muscle, lung and heart tissues. It prevents abortion, nervous trouble, and some types of myopathy (deterioration of the muscle tissue).
It can be found in its natural state mainly in germs of cereals and young grass. Vegetal oils are also a good source of vitamin E.
The digestive organism of the horse doesn’t produce any vitamin E.

Daily allowance:

The quantity of vitamin E is expressed in I.U. (International Units).
1 mg of vitamin A = 1 IU.
The RDA (recommended daily allowance) is between 50 and 100 IU / 500 kilos.


Multiple types of degeneration of the organism, muscular weakness.


No known problem up to now, even with high dosage.

Positive interactions:

Vitamin E improves bioavailability of vitamin C, magnesium, manganese and inositol. It is needed for vitamin D metabolism. It also protects against fat acids (omega-3 and omega-6 against oxidation).

vitamin k

Three forms of vitamins K can be distinguished:
– K1 (Phylloquinone) : produced by plants (lucerne),
– K2 (Menaquinone) : abundantly synthesized by bacteria in the gut flora during the digestion of plants from the alimentary bolus.
– K3 (Menadione) : which is a synthetic form of precursor of active vitamin K (biochemically converted in active vitamin K in the organism).

Attention: mouldy silage can lead to a serious lack.
Ensure supplying with this vitamin when treating with antibiotics.

Vitamin K is indispensable for the formation of blood prothrombin (a protein also called factor II which is directly involved in coagulation). It therefore allows blood coagulation.

It is also involved in bone and vascular metabolisms. Unfortunately, it is inefficient against nose bleeding (epistaxis).

Daily allowance:

The RDA (recommended daily allowance) is 1 mg / 500 kilos.


In normal conditions, the horse doesn’t suffer deficiency.
However, mouldy silage contains anti-vitamin K elements.
A deficiency causes bleedings as well as arterial and bone trouble.


Excess of vitamin K is highly toxic to the kidneys.
The main clinical signs associated with horse intoxication are: renal colic, presence of blood in urine, or electrolytic disturbance.


Minerals are natural elements and are essential for the metabolic functions, since they act as structure components, activate biological reactions and regulate cellular exchanges.

Two categories of minerals must be distinguished. On the one side, the main elements, or macroelements are needed in large quantities and expressed in grams: Calcium, Phosphorus, Magnesium, Sodium, Chloride, Potassium, and Sulphur. On the other hand, the trace elements, or oligo elements are also essential but in very small quantities expressed in milligrams or ppm (1 ppm = 1 part per million = 1 mg / kg): Iron, Copper, Zinc, Manganese, Cobalt, Selenium, lodine, Fluor.

The horses needs for minerals depend on their physiological status (growth, gestation, milking) and their activity.

Too large or too small quantities can be dangerous.


A 500 kilo grown-up horse is made up of 7 kilos of calcium and 4 kilos of phosphorus, which brings [the] a Calcium / Phosphorus ratio of 1.75:1.
CalciumThe Calcium / Phosphorus relationship is well-known and highly important. A major or long-lasting unbalance of this ratio will cause adverse effects on the bone mass.
Indeed, the balance between these two elements directly affects the quality of the skeleton; it makes no matter whether the animal is young, grown-up or old.
This calcium/phosphorus ratio is often quite unbalanced, and not always in the same way. Knowing it will therefore allow to choose the lacking minerals to supplement the feeding with. This supplementation must be done permanently and not in “cures”, as it is part of the normal alimentation.

Practically speaking, if the horse eats grass or is fed hay, it must be given mineral feedstuffs that mainly brings phosphorus, often in the form of calcium phosphates.
It is also recommended to add in the fodder the lacking oligoelements (mainly zinc and copper)

If the horse is active in sports and is given a ration containing mainly cereals (in addition to hay) then a mineral supplementation rich in calcium (carbonates) will have to be selected.
The calcium / phosphorus ratio can vary between 2.1:1 and 1.2:1.
With age, this ratio evolves and reaches 1.4:1 to 1.5:1.

Sodium, potassium and magnesium seem to be somehow influent too.

The optimum of the calcium / phosphorus ratio is 1.5:1 for a resting horse, and 1.8:1 for a breeding mare, a growing young horse or a working horse.
It is also interesting to note that this ratio has an average of 2.3:1 within the hoof.

Calcium is the main component of the bones.  It is directly involved, together with vitamin D, in the conception and care of the skeleton.
Deficiencies in other essential nutriments can also affect the strength of the bones. Examples can be zinc, manganese, niacin (vitamin B3), choline and biotin (vitamin B8).
Finally, calcium is also an essential element needed during muscle efforts.
Digestibility of calcium is around 70%. It is however lower if calcium is given in the form of oxalate (lucerne).

Recommended daily allowance:

A 500 kg resting horse needs 25 to 30 grams of Ca daily.


The bones get thicker and excessively dense, and suros may appear inside the bone cavities. An excess of calcium leads to a deficiency in magnesium, copper, zinc and iron.
Excesses of calcium are less worrying than excesses of phosphorus, as far as the Ca/P ratio is lower than 3:1.


Generally speaking, the needs in cobalt are covered by alimentation. Cobalt is involved in the composition of vitamin B12. It allows its synthesis through the intestinal tract microflora. However, the horse seems to resist more than ruminants to cobalt deficiency.
Cobalt is antianemic as it acts through vitamin B12 on red blood cells.

Daily needs:

0.5 milligrams for a 500 kg resting horse.


Deficiency is rare. Pay attention to excess of calcium.
Delay or disappearance of heats on the mare, nesting defaults.
Tendon, bone, joint and growth disorders.


The toxicity threshold lies between 80 and 100 milligrams, i.e. 200 times the daily needs.


Copper is an anti anemic factor, like iron, cobalt and vitamin B12.

Copper is involved in myelin, the protective sleeve of nervous tissues.
It also favours the synthesis of melanin, pigmentation which colours dander, hair, and the horn.

Well balanced with zinc, it improves the quality of the hoof’s horn. It is also involved in the elaboration of elastine, a protein close to collagen and on which depends the elasticity of large blood vessels and tendons. It stimulates the bone development and strength (against fracture). It avoids protruding cartilage to appear on the fetlocks and hocks, as well as joint cartilage to thicken, which can cause poor balance and lameness.
It is also directly involved in bone vascularisation.

It is therefore an interesting agent to reduce risks of osteochondrosis on foals growing too fast.
Osteochondrosis is also favoured by energy over-nutrition.
Excess of calcium, zinc, iron, vitamins A and D is supposed to worsen the lesions of cartilage by blocking the action of copper.


Daily needs:

Between 150 and 250 mg for a 500 kg resting horse.
The intake of copper must be balanced with that of zinc: the copper / zinc (ratio) must be around 0.25.
Copper might lack due to excess of zinc or other minerals: the animal will therefore be deficient even though it is given a sufficient daily intake.


Deficiency is not rare, mostly on horses mainly fed hay.
The copper content in the fodder can vary greatly between 3 to 8 milligrams per kilo of dry material.
Most of fodder resources lack copper.
The deficiency is visible through lack of growth or even anorexia, immune defect, degeneration of the skin (abscess, hair loss, and pigmentation), degeneration of the hooves, difficult nesting, malformations, cardiac or lung disorders, locomotion troubles, and bone weakness.


The toxicity threshold is around 6 to 8 grams, i.e. 25 to 30 times the daily needs.
It is harmful to the assimilation of zinc and selenium and weakens the horn and bones, amongst others.


An average of 33 grams of iron is found in a 500 kilo horse. 60% of it are located in the haemoglobin, 20% in the myoglobin, and the rest interacts in various biological reactions (enzymes).

Iron plays a major role in the formation of hemoglobin. Hemoglobin carries oxygen from the lungs to the rest of the body and brings carbon dioxide back to the lungs.
All the red blood cells and their hemoglobin are continuously destroyed and regenerated.
Although the red bone marrow is a good store of iron, a daily intake remains necessary and indispensable.

Regarding the myoglobin, it is the main intracellular carrier of oxygen through the tissues. It also stores it in the muscles.

Iron is present in wheat bran (160 mg/kg), millet (90 mg/kg) and oats (42 mg/kg).

Daily needs:

Between 0.5 and 1 gram for a 500 kg resting horse.


Deficiency of iron is quite rare thanks to the plant-eating diet of the horse.
However, when it occurs, deficiency causes anemia, a lowering concentration of hemoglobin, which leads to a deficient transport of oxygen through the blood.
Symptoms are: loss of weight, lack of appetite, important muscle fatigue, tachycardia, and breathing difficulties.


The toxicity threshold is around 10 grams, i.e. 10 to 20 times the daily needs. It causes serious hepatic degeneration.

Excess of iron hampers the assimilation of copper and zinc, at the expense of bone and hoof strength, of hemoglobin production (and anemia occurs paradoxically), and of the elasticity of blood vessels or tendons. It comes together with a lowering of the rate of vitamin E, which predisposes to muscle injury.
Excess can also decrease immunity due to a lack of zinc and vitamin E, which will facilitate infectious complications.


Fluor is mostly known for its toxicity.

Fluorosis appears when fluorine consumption is higher than 50 milligrams per kilo of aliments or 1 milligram per kilo of live weight.

Intoxication may occur in areas with phosphate ore, or when using natural undefluorinated phosphates like mineral supplement, pasturage contaminated with smokes from phosphate-processing plants, or bauxite from aluminium manufacturing.

However, a minimal quantity of fluorine is needed to produce tooth enamel, as well as to reduce osteoporosis on ageing horses.

Daily needs:

1 to 2 milligrams for a 500 kg resting horse.


Dental and skeletal troubles.


The toxicity threshold lies around 500 milligrams, i.e. 100 times the daily needs.
Stiff legs, lameness, bone lesions and deformations, sensitivity to fractures, dental injuries.


Fodders and cakes contain an average of 0.1 to 0.4 milligram of iodine. Seeds contain between 0.02 and 0.06 milligrams.

Soils close to the sea (up to 50 kilometres away) are enriched by the atmospheric iodine contained in rain water.
The highest concentrations are found on the oceanic islands, the South-Pacific coast areas and the saltpetre mines in Chile.

Water only contains an average of 10% of the daily needs in iodine.
On the horse, iodine is mainly absorbed by the large intestine (90%).

Iodine is an important element in the thyroid gland which produces two hormones directly involved in the energy metabolism.
Iodine is also involved in the building of the bone framework through thyroid hormones.

Unlike the other species, the horse is highly sensitive to iodine excess (10 to 100 times more sensitive).

The needs in iodine evolve together with the secretions of the thyroid gland, but also during cold-fighting periods.

Canola, colza, cabbage, and to a lesser extent, soya, are anti thyroid agents.
A finely-dosed supplementation can therefore be recommended, particularly on mares during breeding and lactation periods.

Daily needs:

3 to 4 milligrams for a 500 kg resting horse.


Thyroid gland enlargement, bone and energy troubles, fatigue.
In Canada and the U.S., most of the soils are iodine-deficient, except those exposed to the sea. Horses are therefore exposed to thyroid gland enlargement, although older horses are less.
New-born foals whose mare has been deprived of or excessively fed iodine are more at risk.
High quantities of calcium interfere with iodine resorption.


The toxicity threshold lies around 50 milligrams, i.e. 10 times the daily needs.
Thyroid gland enlargement, energy troubles, deformation of the limbs.


Magnesium is very well digested by horses: up to 60% in fodder and 50% in concentrates.

60 to 70% of the total amount of magnesium is to be found in bones, the rest being distributed in fluids and connective tissues.

Magnesium is involved in neuromuscular tonicity as well as in the assimilation of calcium and phosphorus.

Magnesium also plays an important role in the formation of bones and teeth, as well as in the transmission of nervous impulsions, in the synthesis of hormones and DNA, during reproduction and in the energetic metabolism. It is a co-factor of vitamins B and C.

An increase in the concentration in phosphorus decreases the resorption of magnesium. On the other hand, an increase in the concentration of magnesium in the food ration increases the real digestibility of calcium without modifying that of phosphorus, which will lead to a modification of the calcium-phosphorus ratio.


Deficiency in magnesium is not common, as the needs are most of the time largely satisfied by alimentation, mostly fodder, except young grass. A deficiency leads to a nervous state, cramps and excessive sweating.

Recommended daily allowance:

A 500 kg resting horse needs 7 to 11 grams of Magnesium daily.


Manganese is indispensable to bone development and fertility. Deficiency is extremely rare on the horse.

The quantity of manganese contained in fodder varies between 30 and 45 milligrams per kilo of dry material and usually meets the daily needs.

However, intestinal absorption may be reduced by an excess of calcium, particularly in areas rich in limestone, but also with legume or beet-pulp forages (as zinc).
In those cases, it is recommended to supplement with 50 milligrams of manganese.

On the foal, deficiency delays ossification and thickening of articulations, suros, fetlocks and hocks.


Daily needs:

Between 400 and 500 milligrams for a 500 kg resting horse.


Deficiency is rare. Pay attention to excess of calcium.
Delay or disappearance of heats on the mare, nesting defaults.
Tendon, bone, joint and growth disorders.


The toxicity threshold lies around 10 grams, i.e. 10 times the daily needs.
A major excess disrupts the iron metabolism.


Phosphorus is directly involved in the formation and maintenance of bones and teeth.

It also plays various functional roles.
It is involved, as well as calcium, in the acid-base balance of the digestive tract.

Phosphorus is also a co-factor of several hormones and vitamins B. It is involved in the transport of fats, the cell division, and the energy regulation.

A lack in phosphorus, as well as lacks in calcium or vitamin D, leads to rickets (deformation of the skeleton), and lowers the absorption of fodder.

Phytic acid is the most abundant phosphorus constituent among plants; it is exclusively located in seeds (it sometimes counts for 80 to 90% of the organic phosphorus) and in some tubers.
Phytic phosphorus is located in great quantities in bran and wheat. Phytic phosphorus is up to 30% digestible, while phosphorus under dicalcium or sodium form is up to 60% digestible.

Excess of phosphorus can make bones fragile, although calcium is mainly absorbed in the big intestine under the action of micro intestinal flora.

Recommended daily allowance:

A 500 kg resting horse needs 14 to 20 grams of phosphorus daily.


Excess of phosphorus happens with rations rich in cereals.

An important intake of phosphorus decreases the absorption and retention of calcium, which leads to bone demineralization, skeletal fragility, suros, osteofibrosis (bran sickness, millers’ donkeys’ disease, or big-head disease). This same excess of phosphorus also inhibits the assimilation of magnesium and various trace elements (e.g. zinc) as well as copper and iron.
As a reminder, the optimum Calcium / Phosphorus ratio is 1.5:1.


Potassium acts together with sodium. They are both in charge of keeping the acid-base balance of the body and its fluids.

Potassium by itself allows the transmission of nervous impulsions, muscular contraction (half the amount of potassium is used here), and a good-working renal function.
This mineral plays an important role within the organism. It is part of the enzymatic system involved in the energetic metabolism (carbohydrates included), the transportation of oxygen and carbon dioxide through the blood system, as well as the synthesis of proteins.

It can be estimated that the needs in potassium are met with a usual ration containing at least 50% of fodder. Indeed, fodder is rich in potassium: 21 g/kg of dehydrated grass, 22.8g/kg of lucerne.

The average values of potassium are 10g/kg of vegetable seeds, 12.3g/kg of wheat bran, usually 10.3 g/kg of cakes, but 21.1g/kg of soya and 39.6g/kg of molasses.

Recommended daily allowance :

A 500 kg resting horse needs 25 grams of potassium daily. It can go up to 40 g a day in case of intensive work.


Although quite rare, deficiency in potassium leads to a slowed growth rate, loss of weight, muscle tightness and paralysis, degeneration of organs and cardiac rhythm disorders.


Too large quantities of potassium will cause excretion (elimination) of sodium through the urinary tract and vice-versa.
Excess will interfere with the assimilation of magnesium.

selenium Selenium is a powerful biological antioxidant. Its biological action converges with that of vitamin E and must be proportional to the richness of vegetal oils in polyunsaturated fatty acids (Omega 3-6-9). The latter form the major part of cell membranes and are very sensitive to oxidation.

Selenium, together with vitamin E, protects the cells and particularly red blood cells against the risks of hemolysis (destruction of red blood cells by the liberation of hemoglobin into plasma).
Selenium and vitamin E prevent small hemorrhages and oedema of muscles, liver and pancreas.

Selenium is involved in reducing the risks of muscle strain (blood rush – rhabdomyolysis).

It is also involved in hormonal processes linked to ossification, immunity and reproduction.

Needs in selenium are about 0.1 to 0.2 milligrams, admitting that the ration contains enough vitamin E and other antioxidants compared to the quantity of polyunsaturated fat acids.


Deficiency is due to fodder coming from too primary soils and can be increased by an excess of sulphur (beet pulp too much pressed) or copper.

The concentration of selenium is low in Eastern Canadian soils and in those of many American states. Plants on those soils contain less than 0.05 milligrams, while an adequate rate is estimated to be 0.1 milligram, i.e. more than twice as much. Horses fed hay from pasture, with or without seeds, and not supplemented with selenium risk to face deficiency.

On the other hand, in the South-Western states of America, plants may contain up to 50 milligrams of selenium!
It is therefore imperative in these conditions no to supplement with selenium and to vary the origins of alimentation as the risks of intoxication are truly real.

Daily needs:

0.2 to 0.3 milligrams for a 500 kg resting horse.


Acute myopathy on horses of all ages (serious muscle degeneration), which can be fixed in most cases by injecting vitamin E or selenium. Muscle dystrophy (progressive weakness of the skeletal muscles), reproduction troubles on the mare and stallion. Thyroid gland enlargement.


The toxicity threshold lies around 3 milligrams, i.e. 10 times the daily needs.
Loss of weight, crackling hooves, long bones erosion, hair loss from mane to tail.
In extreme cases the horse may become blind, the breathing rate and the cardiac rhythm may increase, and the horse may suffer diarrhoea and colics.

There have been cases of death by poisoning with selenium in England in the years 1990s. They were due to fodder extremely rich in selenium that was given with extra selenium salt in the ration.


Sodium chloride (cooking salt) is made up of two components (electrolytes or ions), chloride and sodium, which act in harmony or individually in order to ensure the osmotic and ionic balance of cells and resist a changing degree of acidity.
sodiumThe osmotic balance consists in adjusting the ion concentrations on both sides of the cell membrane. If this balance is broken, the cell dies.
Estimates indicate that 50% of sodium is present in bones but cannot be liberated in case of need. A large proportion is located in muscles too. Mare milk also contains a lot of salt.
Sodium chloride plays an important role in the metabolic functions as it is involved in the composition of some organic acids which help digest sugars, fats, and other foodstuffs in the stomach. Sodium also has a fundamental role in muscular contraction.
The food intake is usually too little, as large quantities of sodium chloride disappear with sweating.
Therefore, the needs increase very quickly with physical activity and temperature. The supplementation of sodium chloride has to be controlled on active horses, as their needs are two to three times higher than those of resting horses.
In case of intensive sweating, especially during intensive work under high temperatures, it may be necessary to supply the horse with a supplementation in the form of a medical oral preparation or a bloc of unrefined sea salt (salted stone) or granulates.
Recommended daily allowance:

The RDA is fixed to 25 to 30 grams for A 500 kg resting horse (15 to 45 grams per day depending on the age and the physiological stage) and up to 70 grams for an active horse.


It is noticed by a loss of appetite, shaggy hair and the horse licking the box to compensate. Growth is slowed down as well as milk production. Bones get fragile and in extreme cases the horse can’t coordinate his movements anymore.


Salt is not toxic, but the lethal dose is between 500g and 1kg per day.
The maximal dosage is fixed to 1% of the total weight of the ration in order to avoid indigestion.


Sulfur is one important component of the three amino acids (cysteine, cystinee and methionine) and two vitamins (biotin and B1).

Sulfur is also an essential component of keratine. Indeed, keratine is made up of a great proportion of cystine derived from cysteine. Without supplementation of sulphur through alimentation, the growth of hoof, hair and bristles would be weakened. One must therefore pay attention to the quality of the proteins in the ration.

But sulphur is also involved in various vital functions as it regulates the hepatobiliary secretions (bile), stimulates the breathing of the cells, neutralizes the toxins and favours their elimination, is anti allergic and desensitizing.
It is a fundamental component for the synthesis of proteins.
It is present in many of them (e.g. insulin), and also within the connective tissues, cartilage, tendons, bones and teeth.

Daily needs:

Between 10 and 15 grams for a 500 kg resting horse.

Unlike ruminants, the horse has no specific need of sulphur, but the intake must be done on a daily basis through proteins and sulphured amino acids. Together with zinc, copper, vitamin A and H (biotin), these amino acids are involved in the synthesis of keratin.


Excess of sulphur can be found in some types of pressed or dried beet pulp and hampers the assimilation of copper and selenium.


Zinc is necessary to ossification. It protects against osteoarticular troubles like swollen hocks and fetlocks. It is very useful during growth and reproduction as well as to the immune system.

Zinc affects the production of a high-quality hoof, in synergy with copper and vitamins A and D.

An alimentation rich in calcium and phosphorus can make the needs in zinc increase.

Zinc is also involved in the elaboration of myelin (nerves protective sleeve), hair, horn, bone proteins, in the formation of collagen as well as in the correct vascularisation of cartilage.
It is also indispensable for a good-quality skin.

Daily needs:

Between 600 and 800 milligrams for a 500 kg resting horse.
The supplementation in zinc must be balanced with that in copper: the copper / zinc ratio must be around 0.25.
Zinc may be deficient because of an excessive supplementation in copper or other minerals: the animal is therefore deficient even though it is given a sufficient daily intake.


Deficiency is not rare, even more on horses mainly fed fodder.
The quantity of zinc in fodder varies highly between 15 and 48 milligrams per kilo of dry material.
Most forage resources (hay) are zinc-deficient.

Deficiency leads to growth defect, even anorexia, immune deficit, skin degeneration, hair loss, difficult nesting, and malformations.


The toxicity threshold lies around 5 to 8 grams, i.e. 5 to 10 times the daily needs.
It is harmful to copper assimilation and particularly causes hoof weaknesses, anemia and osteochondrosis on the foal.