Selenium is a trace mineral that horses need every day. It is a strong anti-oxidant, protecting your horse’s cells from damage. It does this through the creation of selenoproteins.
◆︎ Selenoproteins have a number of specific functions:
➡ Muscles: As a powerful anti-oxidant, they help muscles recover faster after exercise.
➡ Immune System: Selenoproteins help modulate the immune response. Examples include:
» Fighting off infections, such as viruses
» Supporting the horse during periods of critical illness.
» Supporting the horse with intestinal inflammation.
» Supporting the ageing horse that has waning immunity.
➡ Reproductive health: Selenoproteins are critical antioxidants for both the mare and the stallion.
◆︎ What are some signs of selenium deficiency?
☛ Muscle weakness, trembling, difficulty moving, tying up
☛ Breathing disorders
☛ Compromised immune system
These are fairly non-specific and can easily be confused with other conditions.
◆︎ How will I know if my forage is selenium deficient?
Selenium in the soil is a good indicator if plants will take it up. The map below shows what areas of the country are deficient in selenium. The blue areas indicate selenium deficiency.
◆︎ How much selenium does my horse need?
Horses need 1-3 mg of selenium daily from all food sources. For areas that are deficient in selenium, 1 teaspoon of Selenium yeast will give about 2 mg of selenium.
Caution: Selenium toxicity has been documented in horses at about 20 mg per day.
Symptoms of selenium toxicity include losing mane and tail, swollen coronary bands, sloughing of hooves, or even death.
◆︎ Take home message:
Selenium is an important trace mineral for the horse. For horses in selenium deficient areas, it can support muscle functioning, a healthy immune response, and healthy reproductive status. When determining the selenium status of your horse’s diet, it’s important to be aware of the geographical area that your hay originated.
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Disclaimer: Statements regarding dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease or health condition.
©Joan Kulifay, MSc. 2025