Selenium is an essential trace mineral for horses—without it, the body cannot function normally. A horse needs selenium only in very small amounts, but its importance for health and performance is fundamental. Selenium functions in the horse’s body primarily as part of the antioxidant defense system. It is essential for the activity of the enzyme glutathione peroxidase, which protects cells from oxidative stress and reduces damage to muscle cells during exertion. Working in synergy with vitamin E, selenium supports normal muscle metabolism and helps the horse recover from training. In addition, it is essential for the reproductive health of breeding horses.
Selenium deficiency is often reflected particularly in the musculature: the horse may feel stiff, sore, or tired, and its performance may not match its normal level. In severe cases, deficiency can cause so-called white muscle disease in foals and young horses, in which muscle tissue is damaged and the heart muscle can also be affected.
Immune defense
Adequate selenium intake is important for a functioning immune system. A deficiency can weaken resistance, meaning the horse becomes ill more easily and recovers more slowly. Selenium also participates in the metabolism of thyroid hormones, which influences the body’s overall energy balance. Reproductive health may also suffer: studies have found links between selenium deficiency and foaling problems, disturbances in fetal growth, and fertility issues.
Deficiency
Symptoms of selenium deficiency can be difficult to recognize, because they often develop gradually and tend to be non-specific. The owner may notice that the horse is less willing to move, recovers more slowly than usual, or that the coat loses its shine. Sometimes the signs can easily be confused with other causes, which is why the most reliable way to determine selenium status is a blood test. Whole-blood selenium concentration or glutathione peroxidase activity are the most reliable indicators of the horse’s selenium stores. A forage analysis also provides clues as to how much selenium the horse is receiving from its diet.
In the Nordic countries, the need is emphasized
In the Nordic countries, selenium supplementation is particularly important because the region’s soil is naturally low in selenium. This is reflected in the selenium concentrations of forage plants and therefore in equine diets. In Finland, the issue has been addressed by adding selenium to fertilizers, but in practice many horses’ diets still fall short without supplementation. For this reason, a selenium supplement is (or should be) part of many horses’ daily feeding—especially if the forage comes from selenium-poor areas.
However, it is important to be aware that selenium has a narrow safety margin: too much can be just as dangerous and can lead to signs of toxicity. Selenium should therefore never be overfed. Excess selenium can cause hair loss, hoof damage, and even life-threatening poisoning. For this reason, it is essential to evaluate the selenium content of the entire diet and account for all sources, such as mineral feeds, concentrates, and supplements.
According to LNRC recommendations, a 500 kg horse needs at least about one milligram of selenium per day, and during heavy workload or pregnancy the requirement may be 2–3 milligrams.
Reproductive health
Various studies have found that selenium deficiency can affect both mares and stallions. In mares, low selenium status may lead to poor conception rates, fetal developmental abnormalities, and problems during foaling. Selenium supports normal metabolism in placental and uterine tissues, and deficiency may increase the risk of issues such as premature placental separation or poor foal vitality after birth. Foals born to selenium-deficient mares may be born with muscle weakness or may be predisposed to a “white muscle disease” type syndrome.
A mare receiving adequate selenium recovers better, and the foal has a higher likelihood of being born vigorous, with good muscle tone and a normal suck reflex. Selenium supports the newborn foal’s muscle and heart function as well as immune defense. In addition, a mare that has received adequate selenium will also have sufficient selenium in her milk to meet the foal’s needs, meaning the foal receives this essential trace mineral immediately at the start of life.
In stallions, selenium supports sperm formation and quality. Selenium-dependent enzymes protect sperm from oxidative stress, which promotes motility and viability. Deficiency can reduce semen quality and thereby lower breeding performance.
Organic vs. inorganic selenium
Organic selenium, such as selenium yeast, contains selenium primarily bound to an amino acid in the form of selenomethionine. This form is absorbed from the intestine in the same way as ordinary amino acids and is stored more effectively in the body—for example in muscles and the liver. When the body needs selenium, it can draw on these stores flexibly.
Inorganic forms, such as sodium selenite or selenate, are absorbed less efficiently and circulate in the blood only for a limited time. They cannot be stored in the same way as amino acids, so their effect is shorter-term and less efficient.
Studies have shown that organic selenium increases selenium concentrations in blood and muscle tissue as well as glutathione peroxidase activity significantly more effectively than inorganic forms, which is why it is now the preferred choice in high-quality equine supplements.
CdG Organic Selenium
CdG Organic Selenium contains organic selenium yeast and chokeberry (aronia). Chokeberry is one of the berries with an exceptionally high polyphenol and anthocyanin content, and it is known as a very strong natural source of antioxidants. When selenium functions as part of the body’s own antioxidant enzyme system (glutathione peroxidase), the polyphenols and anthocyanins in chokeberry complement this defense by acting as direct antioxidants. In other words, they can neutralize free radicals and reduce oxidative stress before these compounds even have time to burden the body’s enzyme systems.
The combination of organic selenium yeast and chokeberry therefore makes the product more than just a selenium supplement: selenium has been shown to improve the horse’s internal antioxidant enzyme defense, and aronia provides a natural, plant-based antioxidant shield. In practical terms, this means the horse receives both an essential trace mineral and the support of a natural “superberry,” particularly in periods of exertion, recovery, and immune maintenance.
Summary
In summary, selenium is one of those nutrients whose adequate intake horse owners should be especially aware of. Under Nordic conditions, selenium supplementation is often necessary to support a horse’s wellbeing, muscle health, and performance. At the same time, it must be remembered that selenium is a trace mineral for which both deficiency and excess can be harmful—balance and careful supplementation are key.
Sources:
- Ishii et al. (2002). “Effects of vitamin E and selenium administration on pregnant heavy draft horsemares on placental retention time and reproductive performance and on white muscle disease in their foals.”
- Thorson et al. (2010). “Effect of selenium supplementation and plane of nutrition on mares and their foals: foaling data”
- Karren et al. (2010). “Effect of selenium supplementation … selenium concentrations and glutathione peroxidase”
“Retained Placenta and Selenium Deficiency in Horses”
UC Davis — “Selenium — an Essential Mineral”
“Selenium for Horses: How Important Is It?”
“Effects of Selenium Source on Mares and Foals”
- Beyond antioxidants: Selenium and skeletal muscle (Wesolowski et al. 2022)
- Dietary selenium improves skeletal muscle mitochondrial density (White et al. 2017)
- Effects of selenium source on measures of selenium status and immune function in horses (Montgomery et al. 2012)
- Effect of selenium supplementation on vaccination response and immune function in adult horses (Brummer et al. 2013)
“Aronia melanocarpa ameliorates gout and hyperuricemia in mice”
“Effects of black chokeberry (Aronia melanocarpa) supplementation on oxidative stress, inflammation and gut microbiota: a systematic review of human and animal studies”
“Designing New Sport Supplements Based on Aronia”
