Vitamins are organic compounds that are essential for all living things. Vitamins have diverse roles within the horse’s body, affecting energy metabolism, growth and repair, muscle function, neurological health, immune function and much more.

Vitamins function as cofactors for metabolic reactions, including the breakdown of sugars and fats for energy, hormone synthesis, nerve impulse transmission, muscle contraction and more.

Your horse’s current vitamin requirements depend on age, exercise level, reproductive status (pregnant and lactating) and health status.

Whether your horse is meeting their requirement for a given vitamin depends primarily on what is in their feeding program, but can also be affected by gut health and endogenous (internal) production.

Other factors such as genetics (breed), nutrient interactions and health status can also play a role in how well the body absorbs and uses vitamins.

Forages can vary greatly in vitamin levels depending on the type of forage and when/how it is harvested and stored. As an example, fresh pasture is generally a good source of Vitamin E, but this vitamin degrades quickly after hay and grasses are cut.

Most horses should receive a vitamin and mineral premix to prevent deficiencies and ensure optimal health. Hoof quality, skin and coat condition, energy levels, mood and resistance to illness are all improved when vitamin and mineral requirements are met.

To find out whether your horse is meeting their vitamin requirements, submit your horse’s diet for analysis by our equine nutritionists.

Vitamins for Horses

The vitamin requirements for horses have been established by the National Research Council through an extensive review of scientific literature. These requirements are published in the Nutrient Requirements of Horses, last updated in 2007. [1]

The vitamins that you horse needs in their diet can be divided into two categories:

Fat-soluble vitamins:

The fat-soluble vitamins include:

  • Vitamin A
  • Vitamin D
  • Vitamin E
  • Vitamin K

These vitamins form solutions when mixed with fats (lipids) and are absorbed and transported in the body similar to fats.

In general, the requirements for these vitamins have been more carefully researched than the water-soluble vitamins.

Fat-soluble vitamins are stored in the body which can result in toxicity issues with excess consumption.

Water-soluble vitamins:

The water-soluble vitamins include:

  • Vitamin B1 (Thiamin)
  • Vitamin B2 (Riboflavin)
  • Vitamin B3 (Niacin)
  • Vitamin B5 (Pantothenic acid)
  • Vitamin B6 (Pyridoxine)
  • Vitamin B7 (Biotin)
  • Vitamin B9 (Folate)
  • Vitamin B12 (Cobalamin)
  • Vitamin C

Vitamin C is made in the liver and typically does not need to be supplied in the horse’s diet to avoid deficiency. However, there may be cases in which supplementation provides an added benefit.

The horse’s hindgut produces significant levels of B-vitamins that the horse can absorb. Requirements for these vitamins are typically met by fibre-digesting microbes.

However, if hindgut function is impaired or nutrient absorption is poor, supplementation may be necessary. Furthermore, supplementation beyond the minimum requirement may support optimal health, such as feeding 20 mg per day of biotin to promote hoof health.

Water-soluble vitamins are not stored in the body and excess amounts are secreted in urine.

Fat Soluble Vitamins

Vitamin A

Vitamin A is most well-known for its role in night vision and eye health. It is also important for reproductive health in mares and for maintaining immune function.

Vitamin A is made from the precursor beta-carotene which is found in high levels in fresh forage and converted to vitamin A (retinol) in the intestine.

Horses grazing on green pasture are likely meeting their vitamin A requirement. Vitamin A is stored in the liver and can be used to meet the needs of the horse when beta-carotene intake is low.

Levels of beta-carotene quickly decline in stored hay. Therefore, vitamin A deficiency is more likely in the wintertime when access to fresh pasture is limited. [2]

Roles:

  • Acts as an antioxidant to neutralize free radicals before they can damage cells
  • Helps cells of the immune system act more efficiently to protect against infection
  • Supports reproductive health in mares and reduces embryonic mortality

Requirements:

Beta-carotene requirements for mature horses at maintenance are based on intake levels required to prevent night blindness. This is the main sign of vitamin A deficiency.

There is also an additional allowance to maximize tissue storage based on research in other animals.

Maintenance: 30 IU vitamin A / kg bodyweight (BW) (15,000 IU for a 500 kg mature horse)

Growth: 45 IU vitamin A / kg BW

Pregnancy and Lactation: 60 IU vitamin A / kg BW (30,000 IU for a 500 kg mature horse).

Some research suggests supplementation with vitamin A and vitamin E can improve reproductive status in mares including more serviced heats and a greater number of live foals.

Work: 45 IU vitamin A / kg BW (22,500 IU for a 500 kg mature horse).

This is not well defined for vitamin A, it is based on assumptions that it would be between maintenance and gestation/lactation.

Sources:

Fresh, green pasture is the best source of beta-carotene, which is converted to vitamin A in the gut.

Supplementation in the form of retinyl-palmitate might be warranted if there is minimal access to fresh pasture and/or if there is greater demand (growth or pregnancy/lactation).

Deficiency Symptoms:

Night blindness is the classical vitamin A deficiency symptom found in most species, including horses. This requires a chronic intake of very low beta-carotene diets.

Less severe deficiency can impair growth and hematopoiesis (formation of blood cells).

Respiratory infections in weanlings have been associated with low vitamin A status. [3]

Vitamin A deficiency has been linked to reproductive failure in several species but requires more research in horses.

Toxicity Symptoms:

Vitamin A toxicity can result in fragile bones, hyperostosis (abnormal calcification of soft tissues), poor skin condition, and malformation of the growing fetus. It might also be involved in developmental orthopedic disease in growing horses.

Upper Tolerable Limit:

16,000 IU/kg of dry matter intake, or approximately 160,000 IU per day for a 500 kg horse.

Vitamin A is important for vision health, immune function and reproductive health in horses. Fresh pasture typically supplies adequate amounts of Vitamin A in the equine diet, but it may need to be supplemented in horses on older hay, in growing horses, or in pregnant or lactating mares.

Vitamin D

Vitamin D exists in two forms for horses: vitamin D2 (ergocalciferol) is produced by fungi that grow on plant material or vitamin D3 (cholecalciferol) that is supplemented in the diet or synthesized in skin.

Vitamin D3 is made in skin when it is exposed to sunlight (ultraviolet light B) which removes 7-dehyrocholestrol from cell membranes in skin. This is converted to vitamin D3 in the liver and further converted to its active form, calcitriol, in the kidney.

Although there are seasonal fluctuations in vitamin D levels, wearing blankets does not appear to significantly affect vitamin D levels in horses. [4]

For most mammals and birds, vitamin D is important for maintaining calcium and phosphorus balance in the body. It acts on the intestine to increase calcium absorption, on the kidney to support calcium resorption, and at the bone to influence calcium and phosphorus mobilization.

In comparison to other animals, horses have much lower levels of vitamin D and its metabolites in blood and higher circulating levels of calcium. [4]

Horses do not appear to rely on vitamin D for calcium absorption in the gut, unlike other animals. They also secrete more calcium in urine than other species.

More research is needed to understand what role, if any, vitamin D plays in maintaining calcium homeostasis in horses. [5]

Roles:

The role of vitamin D in horses is not well-known. It appears to be less important for calcium and phosphorus homeostasis in horses than in other animals. Some other roles that might be important for horses include: [5]

  • Regulation of inflammation
  • Immune system control
  • Anti-proliferative (anti-cancer) effects

Requirements:

6.6 IU / kg BW (3,300 IU per day for a 500 kg mature horse)

Sources:

  • Endogenous production (synthesized within the body) when horses are in sunlight
  • From roughages in the diet
  • Supplementation with vitamin D3 might be warranted for horses living at high latitudes or with minimal exposure to sunlight.

Deficiency:

The most common symptoms of vitamin D deficiency in animals are rickets or osteomalacia, conditions of soft, weak bones. However, this is extremely rare in horses.

Bone growth and development can be impaired when horses are not exposed to any sunlight or vitamin D in the diet, but this is unlikely beyond the experimental setting.

Excess:

Toxicity of vitamin D can occur with extreme over-supplementation. Horses given over 1 million IU of vitamin D3 per day had severe clinical signs including calcification of soft tissues such as the heart.

This also resulted in weight loss, limb stiffness and an elevated heart rate. [6]

Upper Tolerable Limit:

Estimated at 44 IU / kg BW per day, equivalent to 22,000 IU for a 500 kg horse or approximately 2,200 IU / kg dry matter.

The role of Vitamin D in equine physiology is not well-defined, but, in other animals, it is known to support bone health and calcium-phosphorus balance. Vitamin D2 is found in the diet and Vitamin D3 can be synthesized with sun exposure.

Vitamin E

Vitamin E is a potent antioxidant that must be supplied in the diet because horses can not make it in their bodies. It is found in fresh grass and forages.

Horses that are mostly on lush pasture will get enough vitamin E from grazing. However, vitamin E rapidly degrades when grasses are cut for hay. If your horse is fed mostly hay, they likely have low intake of this vitamin.

Low levels of vitamin E can contribute to tying-up after exercise, frequent and prolonged illnesses and worsening of some equine neurological disorders.

To learn more about vitamin E, read our blog post on 8 Science-Backed Benefits of Vitamin E in Horses.

Roles:

  • Anti-oxidant effects that are important for supporting muscle recovery after exercise
  • Important for cells of the immune system to fight illnesses
  • Supports healthy tissues of the nervous system

Requirements:

Minimum requirements are easily met if horses have frequent access to fresh grasses and forages in pasture. However, horses consuming mostly cut hay may be deficient.

Based on the National Research Council’s Nutrient Requirements for Horses (2007) vitamin E requirements are:

Maintenance: 1-2 IU / kg BW (500 – 1,000 IU for a 500 kg mature horse)

Growth: 500-750 IU vitamin E per day for weanlings and yearlings

Pregnancy and Lactation: Minimum of 1,000 IU per day

Work: Minimum of 1,000 IU per day

These requirement levels are the minimum required intake levels to avoid vitamin E deficiency. However, more recent research indicates that several scenarios warrant higher levels of vitamin E intake.

Higher levels can support horses with allergies, equine metabolic syndrome and those recovering from illness. Daily intake of up to 10,000 IU has been shown to be safe in horses.

Sources:

Fresh, lush pasture is an excellent source of vitamin E and may be sufficient to meet the requirements of most horses. Supplemental vitamin E should be provided if horses are mainly consuming hay or on high-grain diets.

Vitamin E supplements are more effectively used by the body if natural forms are used, rather than synthetic forms. Natural vitamin E is most commonly supplemented in the form of d-alpha-tocopherol.

Deficiency:

Vitamin E deficiency can result in muscle soreness and tying-up after exercise, slow recovery from illness and more time spent lying down. A blood test can be used to determine the vitamin E status of your horse.

Vitamin E deficiency can contribute to neurological disorders in adult horses and foals, including equine motor neuron disease and equine neuroaxonal dystrophy. Pregnant and lactating mares should receive supplemental vitamin E to increase levels in the milk.

Excess:

Toxicity is thought to be rare in horses. High dose supplementation above 10,000 IU per day can cause issues with blood clotting, bone mineralization and vitamin A absorption.

Upper Tolerable Limit:

Estimated at 20 IU / kg BW, or 10,000 IU for a 500 kg horse.

Vitamin E is an important antioxidant for horses and supports muscle recovery after exercise. Supplementation is often necessary for horses on hay and exercising animals.

Vitamin K

Vitamin K is well-known as a cofactor for enzymes involved in blood clotting. It also supports healthy blood vessels and bone health.

Vitamin K is found in plants, is made by intestinal microbes and is commonly found in equine feeds. A precise daily requirement has not been established for horses.

Roles:

  • Required for the vitamin K-dependent proteins that are coagulation factors II, VII, IX, and X. These factors are converted to their active form in the liver by a process that requires vitamin K.
  • Activates enzymes that protect against vascular calcification (hardening of blood vessels).[7]
  • Activates osteocalcin, an enzyme which supports strong bones
[8]

Requirements:

In horses, it is presumed that Vitamin K requirements are met from dietary intake and production in the gut.

Some research suggests a diet containing 2.73 mg phylloquinone (vitamin K1) / kg dry matter supported healthy bone function in exercising horses.

Sources:

Vitamin K occurs naturally in plants as phylloquinone (vitamin K1). It is absorbed in the gut and converted to the active form of vitamin K in the liver.

It also exists as a group of compounds called menaquinone (vitamin K2). These can be produced by intestinal microbes and might contribute to the horse’s vitamin K requirements.

Vitamin K3 (menadione) is the synthetic form given in feed and supplements. It is metabolized to the active form menaquinone-4.

Deficiency:

The most common sign of vitamin K deficiency in all animals is impaired blood coagulation.

Moldy, sweet clover hay can contain dicumarol, a compound that interferes with vitamin K metabolism leading to deficiency in this mineral.

Warfarin treatment can also impair blood coagulation by interfering with vitamin K metabolism.

Excess:

Menadione at doses of 1 – 2.5 grams is toxic to horses, causing acute kidney damage. They might also show more subtle signs such as dullness, depression, weakness, lethargy and anorexia. [9] [10]

Vitamin K is involved in blood coagulation, bone health and supporting cardiovascular function. Needs for this vitamin are typically met in the equine diet.

Water-Soluble Vitamins

Water-soluble vitamins have important functions in the body but excess levels are not stored in tissues. Therefore, requirements have not been as carefully established as for fat-soluble vitamins.

The National Research Council’s Nutrient Requirements of Horses (2007) specifies roles, requirements and deficiency of vitamin C, thiamin, riboflavin, niacin, biotin and folate.

Other important B-vitamins that are not as extensively reported on in the NRC include cyanocobalamin, pantothenic acid and vitamin B6.

Vitamin C

Vitamin C, also known as ascorbic acid, is a powerful antioxidant that supports the healthy function of all cells of the body.

Like other water-soluble vitamins, vitamin C is not stored in the body in sufficient amounts and must be provided in the diet on a regular basis. Horses get this vitamin mostly from production in the liver and in most cases this is enough to meet their vitamin C needs.

Roles:

  • Vitamin C is essential for making collagen, an important protein found in cartilage and bone
  • Antioxidant effects support muscle recovery after exercise [11]

Requirements:

There is no vitamin C requirement currently listed by the NRC. It is thought that amounts made in the liver are enough to meet most horse’s needs.

More recently, research recommends the following intake levels for horses in certain circumstances: [11]

In training: 1500 mg per day

Pregnancy: 600 mg per day

Foals: 400 mg per day

Sources:

  • Endogenous production from glucose in the liver
  • Ascorbic acid supplements of 1 gram to 20 grams are thought to be beneficial:
    1. During hot weather
    2. Under stressful conditions such as travel and competition
    3. During rapid growth or periods of intense training
    4. When vitamin C synthesis is impaired

Deficiency:

In many species, vitamin C deficiency results in scurvy, a condition in which poor collagen formation can lead to weak blood vessels, bone, cartilage, tendons and other tissues. This condition has never been reported in horses.

Associations between low levels of vitamin C in the blood and several disease have been made in horses, including:

  • Wound infections after surgery or trauma
  • Epistaxis – bleeding from the nose
  • Strangles – an infectious disease causing abscesses in the upper respiratory tract
  • Acute rhinopneumonia – respiratory infection caused by equine herpesvirus

Excess:

There are no known negative effects of Vitamin C toxicity in horses. Daily doses of 20 g (approximately 44 mg per kg BW) for 8 months caused no negative effects in horses.

Vitamin C is involved in collagen synthesis and immune function. Horses generally obtain adequate amounts but may benefit from supplemental Vitamin C to support exercise performance or during periods of rapid growth.

Thiamin (Vitamin B1)

Thiamin, also known as vitamin B1, is required by key enzymes involved in carbohydrate metabolism which are important for getting energy from sugar. It is high in most cereal grains and their by-products.

Roles:

  • Necessary to support enzymes involved in carbohydrate metabolism including pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase
  • Important for nerve, muscle, and heart function by supporting movement of electrolytes into and out of cells

Requirements:

Requirements are based on levels needed to maintain a healthy appetite, support growth and exercising horses.

Maintenance: 0.06 mg/ kg BW (30 mg per day for a 500 kg horse)

Moderate exercise: 0.1 mg/ kg BW (50 mg per day for a 500 kg horse)

Sources:

  • Dietary sources rich in thiamin include cereal grains (oats, wheat, barley)
  • Cereal grain by-products (wheat bran, wheat middlings, rice bran and brewer’s yeast)
  • Thiamin supplements in the form of thiamin hydrochloride or thiamin mononitrate

Deficiency:

Thiamin deficiency is rare in horses, however, horses cannot rely solely on thiamin production in the hindgut to meet their needs.

The classical sign of thiamin deficiency is beriberi, a degenerative condition that affects the cardiovascular and nervous systems resulting in an elevated heart rate, shortness of breath, numbness and confusion.

When diets are experimentally low in thiamin (1.1 mg / kg DM, approximately 11 mg per day), the following deficiency symptoms can appear in horses:

  • Loss of appetite and weight loss
  • Muscle twitching
  • Ataxia – degenerative disease of the nervous system that causes poor coordination

Thiamin deficiency has been reported in horses that ingest bracken fern or those given the coccidostat (antiprotozoal drug) amprolium. These compounds interfere with thiamin metabolism.

Horses maintained on regular diets without these compounds are unlikely to develop thiamin deficiency.

Excess:

As with other water-soluble B-vitamins, thiamin toxicity is unlikely and has not been reported in horses.

Thiamin is found in high amounts in cereal grains. It is important for the metabolism of energy from foods that the horse eats.

Riboflavin (Vitamin B2)

Riboflavin, also known as vitamin B2, is required by enzymes that make energy from carbohydrates, protein and fat. It is found in legumes such as alfalfa and clover and to a lesser extent in grass hays.

Roles:

  • Is a precursor for the coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) which are important for redox reactions used to make ATP – the main energy currency of cells
  • Is involved in antioxidant processes that use glutathione peroxidase
  • Supports lipid metabolism

Requirements:

The minimal requirement is thought to be 0.04 mg / kg BW (approximately 20 mg per day for a 500 kg horse). Horses consuming forage-based diets are likely easily meeting this requirement.

Sources:

Riboflavin is high in alfalfa and clover, slightly lower in grass hays, and low in cereal grains. The following levels are typical:

  • Alfalfa and clover: ranging from 13 to 17 mg / kg dry matter
  • Grass hays: ranging from 7 – 10 mg / kg DM
  • Cereal grains: ranging from 1.4 – 1.7 mg / kg DM

Considerable riboflavin synthesis occurs in the hindgut, with concentrations in the cecum and colon reaching 7 – 12 mg / kg DM.

Deficiency:

Symptoms of riboflavin deficiency have not been observed in horses even when diets are artificially low in this vitamin.

In other species, riboflavin deficiency can contribute to poor coat and skin quality, and issues with eye health such as light sensitivity and excessive tear production.

Excess:

No reports of riboflavin toxicity exist in horses or most other species.

Riboflavin is important for energy metabolism. This vitamin is found in high levels in alfalfa and clover hays.

Niacin (Vitamin B3)

Niacin, also known as vitamin B3 or nicotinic acid, is required for coenzymes involved in energy production, redox reactions and cell division.

It is found in most feeds and exists in either bound or unbound forms. Only the unbound form can be used by the body.

Roles:

  • Required to form the coenzymes nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) which are crucial electron acceptors for a variety of enzymatic reactions
  • Important for enzymatic reactions involved in nutrient metabolism, cell division, and calcium metabolism
  • Regulate blood flow

Requirements:

No requirements for dietary niacin intake are reported by the NRC Nutrient Requirements of Horses (2007).

Some reports suggest a daily intake of 35 mg of nicotinic acid is sufficient for most horses, based on ranges of requirements for other animals. This intake level is easily met by a typical equine diet.

Sources:

  • Cereal grains are high in nicotinic acid, but up to 90% of it is bound and unavailable to the horse
  • Oilseeds, such as flaxseed, are a good source of nicotinic acid with approximately 40% of it bound
  • Niacin can be synthesized by microbes in the hindgut
  • Niacin can be synthesized from the amino acid tryptophan in the liver. It is estimated that 60 mg of tryptophan are needed to make 1 mg of niacin in the liver
  • Supplementation in the form of nicotinic acid

Deficiency:

Niacin deficiency has not been reported in horses. In other animals, it can cause metabolic disorders that result in lesions in the skin and digestive system.

The amino acid leucine can interfere with niacin production in the liver. Horses on high-protein diets might require supplemental niacin.

Excess:

Symptoms of excess niacin have not been reported in horses.

In other animals, it is suggested that levels above 350 mg / kg BW are toxic (equivalent to 175 grams for a 500 kg horse), resulting in pronounced vasodilation, itchiness and nausea.

Niacin has several roles in the body related to energy metabolism, enzyme function, and redox reactions. Horses on a high-protein diet may need supplemental niacin.

Biotin (Vitamin B7)

Biotin, also known as vitamin B7, is well known to most horse owners as a vitamin that supports hoof health.

It is found in most feedstuffs and commonly supplemented in equine diets. Beneficial effects on hoof growth and strength are noted with supplementation at 20 mg per day for a 500 kg horse.

Roles:

  • Biotin is an important cofactor for four enzymes:
    • Acetyl-coA carboxylase (involved in fat synthesis)
    • Pyruvate carboxylase (involved in glucose production)
    • Propionyl-coA carboxylase (involved in amino acid and cholesterol metabolism)
    • Beta-methylcrotonyl-coA carboxylase(involved in amino acid metabolism)
  • Biotin is also essential for regulating cell division and gene expression

Requirements:

No specific requirement has been outlined by the NRC’s Nutrient Requirements of Horses. However, for optimal well-being biotin supplementation is recommended at 15 – 30 mg per day.

Feeding less than 15 mg is not recommended and unlikely to yield benefits to hoof health.

Typical recommendations for biotin supplementation to support hoof growth and integrity are 20 mg of biotin per day.

Sources:

Biotin is relatively high in fresh alfalfa (0.49 mg / kg DM), moderately high in oats, barley and soybean meal (0.11 to 0.5 mg / kg DM) and low in corn (up to 0.1 mg / kg DM).

Biotin availability from these sources is unknown in horses, but likely highest in corn and soybean meal.

Biotin can be synthesized by microbes in the hindgut, resulting in biotin concentrations in the cecum and colon between 0.2 to 3.8 mg / kg DM. Whether this biotin can be absorbed to significantly impact biotin levels in the body is unknown.

Deficiency:

The most common sign of biotin deficiency observed in other animals is severe dermatitis (inflammation of the skin).

Although this has not been observed in horses, suboptimal intake of biotin likely contributes to other issues. Most notably, poor hoof quality including soft white line and crumbling, fissured hoof horn has been linked to biotin deficiency.

Excess:

No symptoms of excess biotin intake have been reported.

Horses should be fed 20 mg of biotin per day to support optimal hoof growth and hoof quality. This vitamin also plays a role in skin and coat quality.

Folate (Vitamin B7)

Folate, also known as folic acid or vitamin B9, is important for enzymatic reactions that require the movement of single carbon units. Examples of these include DNA and methionine synthesis.

Therefore, folate is important during growth and for tissues that rapidly turn over, such as tissues in the intestine.

Roles:

Folate is important for several processes in the body including:

  • Production of red blood cells
  • Development of the nervous system
  • Synthesis of neurotransmitters
  • Cell division

Requirements:

Folate requirements have not been established for horses. It is thought that microbial synthesis and levels in the diet are sufficient to meet the needs of most horses.

Folate levels in the blood are lower in exercising horses, suggesting they might require higher levels in the diet.

Based on requirements in other animals, the folate requirement for horses is likely approximately 1 mg / kg of DM, or 10 mg per day for a 500 kg horse.

Sources:

Naturally occurring dietary folate exists in a polyglutamate form in which several molecules of the amino acid glutamic acid are linked to the folate molecule.

Information about folate concentrations of common feedstuffs is lacking but it is suggested that folate is higher in alfalfa and timothy hay compared to cereal grains such as corns, oats and barley.

Horses consuming diets high in fresh forage have higher circulating levels of folate than those on consuming hay or high-grain diets.

The microbiome of the horse’s hindgut is able to produce folate, however, levels of absorption are unknown.

Deficiency:

Folate deficiency has not been reported in horses. In other animals, it can cause anemia and poor function of tissues that have rapid turnover (intestinal lining, skin, bone marrow).

In humans, folate deficiency during pregnancy is associated with neural tube defects and fetal growth restriction.

Some drugs used to treat equine protozoal myeloencephalitis (EPM) can interfere with folate synthesis in the hindgut and folate absorption.

Long-term treatment with sulfadiazine and pyrimethamine for EPM caused defects in red blood cells, bone marrow and oral health. However, folic acid supplementation is not recommended in this case as it will compete for absorption with 5-methyl tetrahydrofolate (the active form of folate).

Excess:

No adverse effects of folic acid ingestion have been noted in any species. It is generally considered nontoxic and any excess intake is excreted in the urine.

Folate is important for DNA synthesis and methylation. It plays a role in neurological health and production of red blood cells.

Cobalamin (Vitamin B12)

Cobalamin, also known as vitamin B12, is involved in a variety of enzymatic processes including protein synthesis, carbohydrate and fat metabolism.

This vitamin is not found in plants and must be synthesized in the hindgut using the trace mineral cobalt.

Roles:

  • Co-factor for DNA synthesis
  • Important for the synthesis of myelin which is necessary for normal function of the nervous system
  • Involved in maturation of red blood cells

Requirements:

No specific cobalamin requirement has been established for horses. It is thought that synthesis from cobalt in the hindgut is sufficient to meet the needs of most horses.

The minimum requirement for cobalt is estimated at 0.1 mg / kg DM or approximately 1 mg per day for a 500 kg horse.

Sources:

This vitamin is not found in plant sources, it must be made by microbes in the horse’s hindgut using the micromineral cobalt.

It can be supplemented in the form of cyanocobalamin or hydroxocobalamin. These will be converted to adenosylcobalamin or methylcobalamin which are the active forms in the body.

Deficiency:

No deficiency has been reported in foals or adult horses. In other animals, including ruminants, low cobalt intake can be fatal. However, horses grazing low cobalt pasture that would be deadly for ruminants showed no signs of cobalamin deficiency.

Excess:

Cobalamin excess has not been reported in horses. As with other B-vitamins, excess vitamin B12 is rapidly excreted.

The maximum tolerable limit of cobalt is estimated at 25 mg / kg DM, or approximately 250 mg for a 500 kg horse. This value is based on research in other animals and has not been firmly established in horses.

Cobalamin is not found in plants, but can be synthesized in the hindgut from the trace mineral cobalt. It is particularly important for red blood cells, the nervous system and DNA synthesis.

Pantothenic acid (Vitamin B5)

Pantothenic acid, also known as pantothenate or vitamin B5, is involved in a wide range of metabolic processes. It is found throughout the diet and can be made by microbes in the hindgut.

Roles:

Panthothenic acid is a part of coenzyme A and acyl-carrier protein. These are crucial for numerous metabolic pathways including:

  • Getting energy from carbohydrates, proteins and lipids
  • Communication between hormones and cells
  • Synthesis of fatty acids, thiamin and folic acid

Requirements:

No specific dietary requirements have been established. However, based on observations in Shetland ponies, a daily intake of 0.038 mg per kg BW (approximately 19 mg per day for a 500 kg horse) is adequate to support normal growth and health in the horse. [12]

Sources:

Pantothenic acid is found in cereal grains and is synthesized by microbes in the hindgut.

Deficiency:

No deficiency symptoms have been reported in horses. In other animals, experimental induction of pantothenic acid results in reduced growth rate, low appetite, skin lesions and poor coat quality.

Excess:

No reports of toxicity have been reported in horses. As with other B-vitamins, excess pantothenic acid is easily excreted in urine.

Pantothenic acid is found in cereal grains and can be manufactured in the hindgut. It is involved in energy metabolism, cellular communication and more.

Pyridoxine (Vitamin B6)

Pyridoxine, also known as vitamin B6, is required for several metabolic processes. It plays a role in blood sugar regulation, muscle development, mood regulation, hormone production and joint health.

Roles:

  • Getting energy from carbohydrates, proteins and fat
  • Anti-inflammatory processes
  • Involved in healthy function of the nervous system and immune cells

Requirements:

No specific requirement has been established for horses. It is thought that synthesis by the hindgut and the amount provided by dietary sources are sufficient to meet the needs of most horses.

Sources:

Vitamin B6 is widely found in the diet of horses.

Deficiency:

No deficiency has been reported in horses.

Excess:

No toxicity symptoms have been reported in horses.

Pyridoxine supports hormone production, metabolic health, muscle function and mood balance. It can be synthesized in the hindgut and is obtained readily from the diet.

Summary

As with all other nutrients, it is important to carefully balance vitamin supply with requirements.

Most forages and hays provide adequate energy and protein to meet requirements but fail to supply enough vitamins to optimize health.

In a 2018 study evaluating the diets of 200 horses, in excess of 90% of horses were found to be deficient in at least one major trace mineral or vitamin. [13]

A short-term deficiency might not significantly impact your horse’s health, but, over long periods of time, inadequate vitamin status can negatively impact health.

Whether you use a Mad Barn supplement or a product from another company that you trust, all horses should be fed a mineral and vitamin to ensure there are no gaps in the diet.

To understand whether your horse is meeting their vitamin requirements, you can submit your horse’s diet online for complementary evaluation by our equine nutritionists.

They will help you put together a feeding program that covers all of your horse’s needs.

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References

  1. Chapter 6: Vitamins. Nutrient Requirements of Horses. 2007.
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  3. Greiwe-Crandell, K.M. et al. Seasonal vitamin A depletion in grazing horses is assessed better by the relative dose response test than by serum retinol concentration. J Nutr. 1995.
  4. Breidenbach, A. et al. Peculiarities of vitamin D and of the calcium and phosphate homeostatic system in horses. Vet Res. 1998.
  5. Hymoller, L. and Jensen, S.K. We Know Next to Nothing About Vitamin D in Horses!. J Equine Vet Sci. 2015.
  6. Harrington, D.D. and Page, E.H. Acute vitamin D3 toxicosis in horses: case reports and experimental studies of the comparative toxicity of vitamins D2 and D3 . J Am Vet Med Assoc. 1983.
  7. El Asmar, M.S. et al. Vitamin K Dependent Proteins and the Role of Vitamin K2 in the Modulation of Vascular Calcification: A Review. Oman Med J. 2014.
  8. Wen, L. et al. Vitamin K-dependent proteins involved in bone and cardiovascular health (Review). Mol Med Rep. 2018.
  9. Mohamed, W.A.M. et al. Diagnostic Approach to Nephrotoxicosis with Vitamin K3 in Draft Horses Based on iNOS and Selective Urinary Variables. Adv Anim Vet Sci. 2017.
  10. Menadione(vitamin K3) toxicity in six horses. Can Vet J. 1992.
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  13. Bruggink et al. Diet Evaluation Study of 200 Horses. 2018 unpublished