Why Selenium Is Essential in Your Horse’s Diet
Selenium is a vital trace mineral that plays a key role in maintaining your horse’s health and performance. Most importantly, selenium works in combination with Vitamin E to act as a powerful antioxidant, protecting cells from oxidative stress. Selenium also supports thyroid function, immune system health, and muscle integrity making it essential for horses at all stages of life and work.
What Does Selenium Do for Horses?
- Acts as an antioxidant in partnership with Vitamin E to protect cells from damage
- Helps maintain healthy muscle tissue, including the heart and diaphragm
- Supports the immune system, helping horses fight off infections and recover faster
- Activates thyroid hormones, which are critical for metabolism and energy regulation
- Plays a role in reproductive health and fertility
Selenium and Vitamin E – A Synergistic Pair
Selenium and Vitamin E work hand-in-hand if one is lacking, the other can offer some compensation. However, for optimal health, your horse needs adequate levels of both. Horses on selenium-deficient pastures may still appear healthy if they're grazing fresh grass, which is naturally rich in Vitamin E. Stance Equitec
Vitamin E plus Selenium is a balanced synergistic pair
Are Soils Selenium-Deficient?
In many regions particularly in Australia and parts of New Zealand the soil is low in selenium, and therefore, so are the pastures. Horses grazing on these pastures may not receive enough selenium from forage alone. On the other hand, grains grown on selenium-rich cropping soils may contain moderate selenium levels.
Signs of Selenium Deficiency in Horses
Mild selenium deficiency may show up as:
- Dull coat or poor hair quality
- Weakened immune system
- Reduced fertility in breeding mares
More severe deficiency can result in white muscle disease, which involves muscle degeneration. Symptoms include:
- Poor exercise tolerance
- Stiffness or abnormal gait
- Difficulty swallowing or breathing
- Heart failure in extreme cases
Signs of Selenium Toxicity
While selenium is essential, too much can be toxic. Signs of selenium excess include:
- Hair loss from the mane and tail
- Cracked, sloughing hooves
- Joint erosion and lameness
- In acute cases: staggering, colic, rapid heart rate, diarrhoea, and death
- tying up
Toxicity is rare but serious. It’s important to dose selenium carefully and never double up on multiple selenium-containing products.
How Much Selenium Does Your Horse Need?
The NRC (National Research Council) recommends:
- 1 mg/day for a 500 kg horse at rest
- 2.5–3.5 mg/day for horses in light to moderate work
- A general safe range is 1–10 mg/day
- Toxic levels start at around 20 mg/day. Selenium has a wide safety margin, but monitoring is essential.
Selenium is available in two main forms:
- Organic selenium (from plants like yeast) – better absorption
- Inorganic selenium (e.g., sodium selenite) – commonly found in supplements
How to Test Your Horse’s Selenium Status
To accurately assess selenium levels:
- Use both whole blood and serum/plasma samples
- Whole blood selenium reflects longer-term status
- Serum/plasma selenium may fluctuate with recent intake
- Selenium needs can vary with age, diet, and workload
Repeat testing may be necessary, especially if you suspect deficiency or excess.
Feeding Selenium Safely
To ensure your horse receives adequate but not excessive selenium, feed a balanced vitamin and mineral supplement designed for your horse’s body weight, diet, and activity level.
Always check your pasture and feed sources for regional selenium levels.
