Selenium and vitamin E are essential antioxidant nutrients for all mammals, including horses. Together with vitamin C, they help minimize the damaging effects of oxidative stress in all cells and tissues of the body.

Although these nutrients are required in only low levels in the diet, they have profound effects on the horse’s immune system, muscle function, nervous system, and recovery from illness.

Deficiencies in selenium and vitamin E diminish protection against oxidation, which can contribute to cellular damage and premature aging. Prolonged deficiency in either of these nutrients can result in muscular and neuromuscular diseases.

Horses fed hay exclusively are susceptible to Vitamin E deficiency, as levels of this nutrient diminish when grass is harvested for hay. Likewise, selenium deficiency is common in horses from coastal regions of North America where forages have low concentrations of this trace mineral.

To prevent nutritional deficiencies, supplementation with these antioxidants is often necessary. Obtaining a forage analysis will help you determine nutrient levels in your hay or pasture so you can formulate a balanced diet.

Selenium for Horses

Selenium is an essential trace mineral for horses that plays several important roles in their health and well-being. It supports the immune system and is involved in the production and function of white blood cells, which help fight off infections.

This trace mineral is also a component of the antioxidant enzyme glutathione peroxidase, which helps protect the body from oxidative damage by neutralizing free radicals. Furthermore, selenium is important for thyroid hormone metabolism and plays a role in muscle function.

When selenium’s biological effects were first discovered in the 1930s, it was considered a toxic element because of its association with neuropathy of grazing horses and cattle. [1]

Despite these initial fears about selenium toxicity, it has since been observed that deficiency is a more common concern. In one study, over 37% of adult horses were considered to be selenium deficient. [26]

In the 1950s, scientists discovered the health benefits of selenium when it was found to prevent illnesses in animals and humans. [1]



 

Physiological Roles

Selenium is a critical component of several different proteins in the body that are collectively known as selenoproteins. These proteins include enzymes that are involved in various important bodily functions.

Some of the functional mechanisms of selenoproteins include the following effects: [1]

  • Antioxidant
  • Anti-inflammatory
  • Anti-carcinogenic
  • Anti-viral
  • Anti-bacterial
  • Anti-fungal
  • Anti-parasitic

The best understood and most important physiological role for selenium is as an antioxidant, as part of the enzyme glutathione peroxidase.

Antioxidant protection is particularly important when horses experience increased stress due to factors such as advanced age, exercise, infection or recovery from injury. [2]

As a component of deionidase enzymes, selenium is also necessary for regulation of thyroid hormone production. The thyroid hormones, triiodothyronine (T3) and thyroxine (T4), are key regulators of animal development, growth, and metabolism. [1]

Selenium in the Equine Diet

Selenium concentrations in forages (such as hay and pasture grass) can vary widely based on the selenium content in the soil where they are grown.

Some parts of North America (especially coastal regions) have soils with very low selenium levels, while central North America tends to have adequate selenium levels in soil. Soil concentrations range from 0.1 parts per million (ppm) in deficient areas to over 10 ppm in selenium-rich areas. [3]

Selenium Map of Canada & the USA | Mad Barn USA

Low Selenium Areas

Soils that contain between 0.1 to 0.6 ppm selenium are considered deficient, resulting in forages with inadequate selenium concentration. Areas with low selenium content in the soil include: [3]

  • The Pacific Northwest
  • The Great Lakes region
  • The Eastern seaboard of Canada and the US

Other areas known to have low concentrations of selenium in the soil include central Asia, Australia, Africa, and parts of South America. [4]

High Selenium Areas

Areas with high selenium concentrations typically include the midwestern states in the US. Horses consuming forages grown in soils from these regions may not need supplements to meet their nutritional requirement.

However, in rare cases, forages and other crops grown in these regions can accumulate selenium to the point of being toxic to animals.

In a U.S. survey of selenium toxicity and deficiency in a variety of animals, disease due to selenium deficiency were reported in 46 states. Naturally occurring selenium toxicity was rare, only reported in 7 states, whereas toxicity due to over supplementation was reported in 15 states. [27]

Other factors, including soil characteristics and weather conditions, also impact how much selenium accumulates in plants. For example, plants grown in alkaline soils (pH > 7.0) or during periods of low rainfall can accumulate higher levels of this trace mineral, potentially contributing to selenium toxicosis in animals. Such conditions are common in areas like South Dakota. [3]

On the other hand, Hawaii is known to have high selenium soils, but crops grown there typically do not have toxic levels of this mineral. This is because Hawaii tends to have more acidic (pH 4.5-6.5) soils, high iron levels and humid conditions, all of which reduce the accumulation of selenium in plants. [3]

Forage Testing

Given the significant geographical differences in the selenium content of forages, it is recommended to submit a forage sample for analysis to determine levels in your horse’s forage. Most laboratories offer selenium analysis for an additional fee.

Selenium content in forages will typically be indicated in a hay analysis report as milligrams per kilogram (mg/kg) or parts per million (ppm). These units of measurement are equivalent.

On a dry matter basis, selenium levels in hay can generally be classified as follows: [3]

  • Deficient: less than 0.1 ppm
  • Marginally Deficient: between 0.1 – 0.199 ppm
  • Adequate: between 0.2 – 0.499 ppm
  • Toxic: greater than 0.5 ppm
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Selenium Status in the Horse

Blood tests can be used to assess your horse’s selenium status.

The following clinical reference ranges for selenium levels in serum (blood) have been proposed for horses: [5]

  • Deficient: less than 0.0053 ppm
  • Marginal: 0.0053 – 0.12 ppm
  • Adequate: 0.14 – 0.25 ppm

Hair analysis might be useful to assess chronically high selenium intake, but is likely not effective for measuring selenium status in horses consuming typical levels of this mineral. [6]

Forms of Supplemental Selenium

If your horse is consuming selenium-deficient forages, you will need to provide them with a supplemental source of this trace mineral to ensure adequate intake.

Most complete feeds, ration balancers and vitamin/mineral supplements sold in North America contain added selenium of varying concentrations.

However, the form of selenium used in these products impacts its absorption and utilization in the body. In general, organic selenium sources (compounds that contain carbon) are more bioavailable than inorganic forms. [7]

Organic Sources

Plants accumulate selenium in the form of selenomethionine – a natural compound that consists of the amino acid methionine with a selenium atom in place of sulfur. Selenomethionine can also be added directly to animal feeds as an organic source of selenium.

Selenium-enriched yeast is another popular supplement for equine diets. This is produced by growing yeast in a selenium-rich medium to enable accumulation of selenized proteins, which are highly bioavailable to the horse. [7]

Organic forms of selenium are considered safer for the horse and less likely to contribute to toxicity.

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Inorganic Sources

Mineral salts of selenium are inorganic forms of this mineral that are extracted from the earth through mining. Inorganic selenium sources include:

  • Selenate
  • Selenide
  • Selenite

Because these forms are less bioavailable, nutritionists recommend choosing a feed or supplement with higher quality organic selenium.

Vitamin E for Horses

Vitamin E is an essential nutrient required in the diets of all animals, including horses. It is a potent antioxidant, supports the immune system, and plays a role in muscle function.

This vitamin was first identified in 1922 when researchers discovered that the fat-soluble portion of lettuce leaves and alfalfa meal was able to restore fertility in previously sterile animals. [8]



 

Physiological Roles

Similar to selenium, the main role of vitamin E in the horse’s body is as an antioxidant.

As a fat-soluble molecule, vitamin E primarily resides in fatty cell membranes, where it protects them from free radical damage and oxidative stress. [8]

Vitamin E also supports anti-inflammatory pathways and is important for muscle recovery after strenuous exercise.

Vitamin E in Forages

Fresh pasture is a good source of vitamin E for horses. Healthy horses grazing on lush pasture likely do not require supplementation to meet their daily requirement. [9]

However, this vitamin degrades over time when grass is cut for hay. [8][10] On average, grass hay contains 85% less vitamin E than fresh grass. Horses consuming a hay-only diet require a vitamin E supplement to avoid a nutritional deficiency. [5]

Plant maturity also influences the vitamin E content of forages. Vitamin E is mostly found in the leaves, rather than the stems of forage plants. Therefore, plants with higher abundance of leaves or blades have higher concentrations of vitamin E. [28]

As grasses mature they become stemmier and therefore have lower vitamin E content. Mature grasses may contain 90% less vitamin E than young grasses. [10]

When evaluating pasture, you can expect that fresh grass that has not yet reached the seeding stage will have higher vitamin E content than stemmy, mature grass.

Vitamin E Status in the Horse

Vitamin E levels can be measured in the horse’s blood to determine whether they are deficient. The following clinical reference ranges for horse serum vitamin E have been proposed: [5]

  • Deficient: less than 3480 micromoles/L
  • Marginal: between 3480 – 4643 micromoles/L
  • Adequate: between 4644 – 23,220 micromoles/L

If your horse is deficient in vitamin E, your veterinarian may recommend a period of supplementing with higher doses and retesting after several months. [19] Consult with your veterinarian for an individual treatment plan.

Forms of Supplemental Vitamin E

There are eight different forms of Vitamin E, consisting of four tocopherols (alpha-, beta-, gamma- and delta-tocopherol) and four tocotrienols (alpha-, beta-, gamma- and delta-tocotrienol).

Of these, alpha-tocopherol is considered the “true” vitamin E and is the form most abundant in forages and grains. The other forms are considered less effective, with only 1 – 40% of the bioactivity of alpha-tocopherol. [8]

Because hay is known to be deficient in vitamin E, this nutrient is included in most commercial equine feeds and vitamin supplements. It is commonly bound to acetate or succinate to improve its shelf life.

Natural vs Synthetic

Vitamin E is available in both natural and synthetic forms, which differ in their chemical structure and bioavailability.

Natural vitamin E is denoted as d-alpha-tocopherol whereas synthetic vitamin E is denoted as dl-alpha-tocopherol. Natural vitamin E is considered more bioavailable because it is more effective at raising plasma levels in horses than synthetic forms. [11]

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Nutritional Deficiency

Adequate levels of selenium and vitamin E are essential in the equine diet to prevent health issues related to their deficiency.

Deficiencies in selenium and vitamin E are most commonly associated with neuromuscular diseases in horses. Deficiency is most common in horses on a forage-based diet who do not receive adequate supplementation.

However, not every horse with a deficiency will show signs of disease. Some deficiencies are subclinical, meaning there are no outward signs, but optimal physiological function of the horse can still be impaired.

In these cases, a deficiency may not become apparent until the horse experiences some external stressor, such as an illness.

Disease development may also depend on: [5][12]

  • Horse’s age
  • Genetic predisposition to disease
  • Duration and severity of deficiency
  • Presence of other nutritional deficiencies or excesses

Signs of Deficiency

It is important to understand that deficiencies in vitamin E and selenium can result in severe and often irreversible disease in horses. Thus, it’s crucial to prevent deficiencies by maintaining proper nutrition.

Clinical signs of selenium or vitamin E deficiency may include the following: [13]

  • General weakness
  • Muscle atrophy
  • Rhabdomyolsis episodes (tying up)
  • Abnormal gait or incoordination (ataxia)
  • Muscle tremors
  • Cardiac dysfunction

If you suspect your horse has a vitamin E or selenium deficiency, consult with your veterinarian to assess their levels of these nutrients. Your veterinarian will be able to provide you with an accurate diagnosis and help you determine the right treatment plan. [13]

The following diseases are associated with selenium and/or vitamin E deficiencies in horses:

  • White Muscle Disease
  • Equine Motor Neuron Disease
  • Equine Degenerative Myeloencephalopathy
  • Equine Neuroaxonal Dystrophy

White Muscle Disease

White muscle disease (WMD), also known as Nutritional Myodegeneration, is a disease that affects skeletal and cardiac muscle in foals. Most cases of WMD occur in foals less than two months old, although it can also occur in mature horses that are chronically deficient in selenium. [14]

Young, fast-growing foals nursing from dams with insufficient selenium and vitamin E during pregnancy are most often affected. [14]

Common clinical signs of white muscle disease include: [14]

  • Recumbency (lying down)
  • Elevated heart rate
  • Failure to suckle
  • Difficulty swallowing
  • Respiratory distress
  • Discolored (red to brown) urine

Foals with WMD are typically treated with intramuscular selenium injections. This method has been shown to restore normal selenium levels in blood within 10 – 30 days. [15]

Vitamin E supplementation, supportive therapy and antibiotics may also be necessary to improve the prognosis for foals affected by WMD.

If identified early and treated quickly, white muscle disease may be reversible. However, the overall mortality rate ranges from 30 – 45%, highlighting the importance of proper nutrition for pregnant broodmares. [14]

Equine Motor Neuron Disease

Horses with a chronic vitamin E deficiency lasting more than 18 months can develop Equine Motor Neuron Disease (EMND). This disease involves degeneration of the nerves that signal to muscles, known as motor neurons. [16]

Clinical signs of EMND become noticeable once horses have lost approximately 30% of their motor neurons. Common signs include: [16][17]

  • Weight loss
  • Standing with legs together and frequent weight shifting
  • Low head and neck carriage
  • Muscle atrophy
  • Muscle tremors
  • Progressive weakness
  • Abnormal sweating

EMND usually affects older horses, with the risk peaking around age 16. For unknown reasons, it may be more prevalent in certain breeds, including Standardbreds, Quarter horses, and Thoroughbreds. [16]

EMND is usually diagnosed with bloodwork to assess vitamin E status and detect muscle damage. More advanced diagnostics include muscle and nerve biopsies to evaluate nerve damage. [16][17]

Treatment of EMND involves feeding the horse a diet with higher levels of natural vitamin E by allowing access to fresh pasture grass and providing supplements. [29]

Severely affected horses may require vitamin E injections administered by their veterinarian. For horses that lack access to fresh green grass, supplementation with natural vitamin E (d-alpha-tocopherol) is necessary. [12][17]

Recovery for Equine Motor Neuron Disease is often slow, even with proper treatment. Regular follow-up bloodwork is required to adjust dietary vitamin E levels. [16][17]

Studies show the following outcomes of EMND treatment in horses: [17]

  • 40% show improvement
  • 40% have stabilized symptoms
  • 20% experience worsening conditions

Horses that experience stabilization of symptoms can have a good quality of life, but they should not be used for performance or riding as they may have ongoing weaknesses. [17]

Equine Degenerative Myeloencephalopathy

Vitamin E deficiency can also lead to a condition known as Equine Degenerative Myeloencephalopathy (EDM). EDM affects neurons in the brainstem and spinal cord. [18]

EDM is characterized by a loss of coordination (ataxia), an abnormal stance at rest and proprioceptive deficits (difficulty with perception of body position and movement).

Horses with EDM may also have a diminished or absent fight-or-flight response to threats. [19]

Some breeds may be genetically predisposed to EDM including Quarter horses, Appaloosas, Morgans and Standardbreds. [19]

EDM is most common in young, growing horses (from 6 to 24 months of age), but it can also occur in older horses (from 5 to 10 years of age).

Once the horse loses muscle coordination, vitamin E supplementation will likely not improve neurological deficits. For the best treatment outcome, foals should have their vitamin E status assessed within the first four months of life. [19]

Ensuring adequate vitamin E intake during pregnancy and for the first three years of life is critical to maintain normal neurological function in genetically susceptible foals. [19]

Equine Neuroaxonal Dystrophy

Equine Neuroaxonal Dystrophy (eNAD) is a very similar condition to EDM. Researchers believe that eNAD is the precursor to EDM.

In horses with eNAD, the neuronal damage is confined to the medulla oblongata (a part of the brainstem). In comparison, EDM involves more widespread neuronal damage. [19]

Equine Neuroaxonal Dystrophy occurs primarily in young horses and appears to have a genetic basis. However, the onset of disease is triggered by a vitamin E deficiency. [20]

The most visible symptom of eNAD is lack of coordination. Horses may stand with their front legs too far apart or too close together. They may also have difficulty with hills and lack coordination while making tight turns. [21]

Clinical signs vary greatly from case to case. Some horses exhibit mild performance problems while others experience severe debilitation. [21]

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Selenium and Vitamin E Toxicity

Whenever supplementing nutrients in your horse’s diet, it is important to provide the correct amount as determined by your horse’s body weight, physiological status and activity level.

Over-supplementing with vitamins and minerals could result in toxicity. Working with an equine nutritionist can help you ensure you feed your horse exactly what they need.

Excess Selenium

Horses need only trace amounts of selenium in their diet to meet nutrition requirements, and this mineral has a relatively narrow margin of safety.

Feeding as little as 1 mg per day is sufficient to avoid deficiency, and the maximum tolerable intake level is 20 mg per day for the average-sized horse. [22] Feeding more than this amount can result in toxicity.

Chronic selenosis, also known as alkali disease, occurs when horses consume excess selenium from feeds, forages and supplements over a prolonged period. [22] While selenium poisoning is usually a chronic condition, in rare cases it can occur due to an acute overdose.

The risk of selenium poisoning is higher when feeding inorganic sources, such as sodium selenite. The metabolism of inorganic forms of selenium generates metabolites that can be harmful to the horse’s body.

Organic sources, such as selenomethionine and selenized yeast, do not form the same metabolites and are less toxic to cells, even at high doses. [25]

High-Selenium Plants

Besides forages grown in high selenium areas, certain plants naturally accumulate high levels of selenium and can cause toxicity if consumed in excess. These plants are most commonly found in the American Mid- and Southwest.

Some of these plants include: [23]

  • Astragalus (locoweeds)
  • Xylorhiza spp. (woody aster)
  • Stanleya spp. (prince’s plume)
  • Oonopsis (false golden weed)
  • Machaeranthera spp. (tansy aster)
  • Haplopappus spp. (golden weed)
  • Atriplex spp. (saltbush)
  • Aster spp. (aster)
  • Castilleja spp. (prairie fire)
  • Grindelia spp. (gumweed)
  • Comandra spp. (bastard toadflax)

If you suspect your horse may have selenium toxicity, inspect your pastures and hay for any of these plants and take measures to reduce their abundance or source alternative forage.

Signs of Selenium Toxicity

Signs of excess selenium consumption in horses include: [22][23]

  • Hair loss in mane and tail
  • Transverse hoof cracks
  • Lameness
  • Distorted hoof wall
  • Excess salivation
  • Profuse sweating

An acute (sudden) overdose of selenium can be fatal. In such cases, clinical signs may include a staggering gait, blindness, labored breathing, respiratory failure, muscle tremors, and collapse. [22]

There is no specific treatment for selenium toxicosis. However, dietary sulphates may be helpful by competing with selenium for incorporation into amino acids. [22]

If selenium toxicity is suspected, exposure should be eliminated by changing your horse’s feed, hay, pasture, or supplements. Horses with hoof damage may need pain management and therapeutic trimming to support recovery. [23]

Excess Vitamin E

According to the National Research Council’s Nutrient Requirements of Horses, vitamin E is not toxic to horses even at high intakes. [22]

However, research in other animals shows evidence of impaired blood clotting and bone mineralization when vitamin E is fed at a concentration above 1,000 IU per kg of dry matter.

For this reason, the safe upper limit of vitamin E in equine diets is set to the same level, equivalent to roughly 10,000 IU per day for the average-sized horse. [22] Fortunately, vitamin E toxicity is extremely uncommon in horses.

Selenium and Vitamin E Requirements

Your horse’s selenium and vitamin E requirements are determined based on their body weight and physiological state.

Selenium Requirement

Equine dietary requirements for vitamins and minerals are established by the NRC’s Nutrient Requirements of Horses. [22]

The NRC’s selenium requirement is based on the daily intake of this mineral needed to avoid symptoms of deficiency, namely to prevent white muscle disease.

For a typical 500 kg (1,100 lb) adult horse at maintenance (not exercising), the NRC requirement is 1 mg of selenium per day. [22]

However, to support optimal immune function, 3 mg of selenium per day is recommended. All horses benefit from this increased level, particularly those experiencing stress or immune challenges, such as exercising horses, pregnant mares and chronically ill horses. [22]

Vitamin E Requirement

For a mature horse at maintenance, the vitamin E requirement set by the NRC is at least 1 IU per kg of body weight.

This means that a mature horse weighing 500 kg (1,100 lb) would need a minimum of 500 IU of vitamin E per day. [22]

Foals, horses in work, and pregnant or lactating mares need substantially more vitamin E to prevent deficiency: [22]

  • Weanlings and yearlings: Between 500 – 750 IU per day
  • Horses in work: At least 1,000 IU per day
  • Pregnant mares: At least 1,000 IU per day, but up to 5,000 IU
  • Lactating mares: At least 1,000 IU per day

Unit Conversion

The amount of vitamin E listed on a feed tag may be presented in milligrams (mg) or International Units (IU), making it difficult for horse owners to compare feed values. Further complicating matters is the difference in biological activity between natural and synthetic forms of vitamin E.

The International Unit (IU) is used to provide a standard unit of biological activity for certain vitamins. To convert mg of vitamin E to IU, use the following calculations: [8]

  • Natural vitamin E: 1 mg of d-alpha-tocopherol is equivalent to 1.49 IU
  • Synthetic vitamin E: 1 mg of dl-alpha-tocopherol is equivalent to 1.10 IU

This calculation highlights the greater biological activity of natural vitamin E compared to synthetic vitamin E, since 1 mg of the natural form yields more IUs than the synthetic form.

Selenium and Vitamin E Supplements

Most horses in North America require selenium and vitamin E supplementation in the diet at least for part of the year to meet their nutrition requirements.

Horses with access to fresh, green pasture for more than 6 hours per day likely do not need supplementation. Grazing on pasture provides roughly 2,000 IU of vitamin E per day. [24]

However, those with limited pasture access, mature grass pasture, or a hay-only diet are likely to be deficient in vitamin E. [5]

Selenium levels in forage depend on where the forage is grown and should be assessed via hay analysis. To determine your horse’s total selenium intake, an equine nutritionist will factor in how much hay your horse consumes as well as other components of the diet.

Choosing Supplements

When comparing supplements or complete feeds, always look at the ingredient list to determine whether the product contains organic or inorganic forms of selenium and natural or synthetic forms of vitamin E.

Organic forms of selenium, such as selenized yeast, are more bioavailable than inorganic forms, such as sodium selenate or selenite. Organic selenium is better absorbed and offers superior antioxidant protection.

Avoid mineral blocks as a source of selenium. Minerals blocks are insufficient for horses, especially for those in low selenium areas. [13]

Horses getting most of their forage as hay likely need vitamin E supplementation. Look for products that provide d-alpha-tocopherol, which is the natural form of vitamin E and is more effective than synthetic forms.

You can either choose single-ingredient supplements that provide selenium or vitamin E on their own or a complete vitamin and mineral supplement to supply other required nutrients and balance your horse’s overall diet.

Mad Barn’s AminoTrace+ is a comprehensive vitamin and mineral formula that provides 2 mg of organic selenium and 1,250 IU of natural vitamin E per serving. AminoTrace+ also contains 100% organic trace minerals, a complete profile of B-vitamins, as well as high levels of probiotics to support gut health.

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For horses that require additional vitamin E, one of the following supplements can be added to the diet to increase intake:

  • W-3 Oil – a fat supplement that provides 1,500 IU of natural vitamin E per serving. W-3 oil also contains the omega-3 fatty acid DHA to support joint health and coat quality.
  • Natural E / Organic Se – a pelleted supplement that provides natural vitamin E and selenium-enriched yeast. Serving sizes can be adjusted to match the horse’s requirement.
  • Natural Vitamin E – a powdered supplement providing pure natural vitamin E with no fillers or additives. This supplement can be top-dressed on feed for easy administration.

Consult with your veterinarian and work with an equine nutritionist to make sure your horse is getting the right amount of selenium and vitamin E in their diet. You can submit your horse’s diet online for a free consultation with our expert nutritionists.

Summary

  • Selenium and vitamin E are two important antioxidant nutrients in the equine diet
  • Many horses require supplementation with these nutrients to prevent deficiency
  • Deficiencies in selenium and vitamin E typically manifest as neuromuscular disorders, including white muscle disease and equine motor neuron disease
  • Selenium and vitamin E toxicity is most likely to occur due to over-supplementation or by consuming forages from areas with excessive soil selenium
  • Choose organic selenium supplements and natural forms of vitamin E when formulating your horse’s diet

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References

  1. Combs, Jr. G.F. Biomarkers of Selenium Status. Nutrients. 2015.
  2. Culhuac, E.B. et al. Influence of Dietary Selenium on the Oxidative Stress in Horses. Biol Trace Elem Res. 2023. View Summary
  3. Saha, U. et al. Selenium in Animal Nutrition: Deficiencies in Soils and Forages, Requirements, Supplementation and Toxicity. Int J Appl Agri Sci. 2016.
  4. Bazzano, M. Selenium and Vitamin E Concentrations in a Healthy Donkey Population in Central Italy. J Equine Vet Sci. 2019. View Summary
  5. Muirhead, T.L. et al. The selenium and vitamin E status of horses in Prince Edward Island. Can Vet Journal. 2010. View Summary
  6. Davis, T.Z. et al. Analysis in horse hair as a means of evaluating selenium toxicoses and long-term exposures. J Agric Food Chem. 2014.View Summary
  7. Calamari, L. et al. Effect of selenium source and dose on selenium status of mature horses. J Anim Sci. 2009. View Summary
  8. Shastak, Y. et al. A Century of Vitamin E: Early Milestones and Future Directions in Animal Nutrition. Agriculture. 2023.
  9. Blakley, B.R. and Bell, R.J. The vitamin A and vitamin E status of horses raised in Alberta and Saskatchewan. Cant Vet J. 1994.View Summary
  10. Lindqvist, H. alpha-Tocopherol and beta-Carotene in Forages and their Utilisation by Dairy Cows in Organic Production. Swedish University of Agricultural Sciences. 2012.
  11. Pagan, J.D. et al. Form and source of tocopherol affects Vitamin E status in Thoroughbred horses. Pferdeheilkunde. 2005.
  12. Vitamin E In Horses. UC Davis Veterinary Medicine.
  13. Pitel, M.O. et al. Influence of specific management practices on blood selenium, vitamin E, and beta-carotene concentrations in horses and risk of nutritional deficiency. J Vet Intern Med. 2020. View Summary
  14. Delesalle C. et al. White muscle disease in foals: focus on selenium soil content. A case series. BMC Vet Res. 2017. View Summary
  15. Wichtel, J.J. et al. The effect of injectable barium selenate on the selenium status of horses on pasture. NZ Vet J. 1998. View Summary
  16. Divers, TJ. et al. Equine motor neuron disease. Vet Clin North Am Equine Pract. 1997.View Summary
  17. Divers, TJ. et al. Equine Motor Neuron Disease: A Review of Clinical and Experimental Studies. Clin Tech Equine Pract. 2006.
  18. Divers, T.J. et al. >Evaluation of the risk of motor neuron disease in horses fed a diet low in vitamin E and high in copper and iron. American J of Vet Research. 2006. View Summary
  19. Burns, E.N. and Finno, C.J. Equine degenerative myeloencephalopathy: prevalence, impact, and management. Vet Med (Auckl). 2018. View Summary
  20. Finno, C.J. and Burns, E.N. Equine Neuroaxonal Dystrophy and Degenerative Myeloencephalopathy. Vet Clin North Am Equine Pract. 2022. View Summary
  21. Horse Report. University of California, Davis School of Veterinary Medicine. 2018.
  22. National Research Council Nutrient Requirements of Horses: Sixth Revised Edition. 2007.
  23. Bischoff, K. Selenium Toxicosis in Animals. Merck Veterinary Manual. 2022.
  24. Finno, CJ et al.Blood and Cerebrospinal Fluid a-Tocopherol and Selenium
    Concentrations in Neonatal Foals with Neuroaxonal Dystrophy
    .J Vet Intern Med. 2015. View Summary
  25. Mezes, M. and Balogh, K. Prooxidant mechanisms of selenium toxicity – a review. Acta Biologica Szegediensis. 2009.
  26. Streeter, RM. et al. Selenium deficiency associations with gender, breed, serum vitamin E and creatine kinase, clinical signs and diagnoses in horses of different age groups: A retrospective examination 1996–2011. Equine Veterinary Journal. 2012.View Summary
  27. Edmonson, AJ. et al. Survey of state veterinarians and state veterinary diagnostic laboratories for selenium deficiency and toxicosis in animals. J Am Vet Med Assoc. 1993.
  28. Zeyner, A. Harris, P. 9 – Vitamins. Equine Applied and Clinical Nutrition. 2013.
  29. Mohammed, H.O. et al. Vitamin E deficiency and risk of equine motor neuron disease. Acta Vet Scand. 2007. View Summary