Selenium Toxicity in Horses: What It Looks Like and How We’re Helping Chester
Yesterday at the auction, we hadn’t planned to bring home five horses (yes, five!), but one gelding made sure we couldn’t leave without him.
When Chester went through the ring, we honestly weren’t paying close attention anymore. We had already purchased several horses and were focused on making sure we had the resources to care for them. By the time we realized how badly he was moving, the bidding was already over.
Afterward, we approached the broker who had purchased him and simply asked what his price would be. He didn’t have to sell him, but he was willing. At first, he asked just $50 over his purchase price—a fair request—but after seeing Chester with us, he even waived that extra. It was a truly kind gesture, and we’re grateful.
At first, we worried about founder. But when we got a closer look, it was clear this wasn’t laminitis. Chester is showing the classic, heartbreaking signs of selenium toxicity—something many South Dakotans know by its cattle name, “alkali disease.”
What is Selenium Toxicity?
Selenium is one of those minerals where balance matters. Horses need it in very small amounts for healthy muscles and immune function. But too much is poisonous, and in parts of South Dakota, the soil, water, and grasses already carry naturally high selenium levels.
That means a horse here can get an overdose just by grazing on the wrong pasture or eating the wrong hay. And while supplementing selenium is common in many states, here it can push a horse into dangerous territory.
👉 A tip for horse owners everywhere: always research your own region’s needs before adding supplements. In some parts of the country, selenium deficiency is a real and serious problem, and supplementation is essential. But in high-selenium states like South Dakota, the same advice could have devastating results.
👉 And for local horse owners specifically: many Vitamin E supplements come blended with selenium, because the two work together as antioxidants and are often prescribed in selenium-deficient regions. But in our area, that added selenium could tip a horse into toxicity. If your horse needs Vitamin E support (such as in neurological or growth-related cases), look for a product that is Vitamin E only.
What Selenium Toxicity Looks Like
Chronic selenium toxicity shows up slowly, often mistaken for other issues. Things to watch for include:
- Loss of mane or tail hair
- Stiffness, lameness, or reluctance to move
- Hooves cracking, breaking, or even sloughing off
- Weight loss or poor body condition
Chester’s hooves tell the story vividly: deep cracks, walls sloughing away, and pain with every step. Once hooves are this compromised, recovery is extremely difficult.
What We’re Doing for Chester
Here’s where we’re especially grateful for the partnerships we’ve built. Our veterinarian is the same one who works the auction, pulling coggins and health papers for the horses passing through. We were able to speak with him directly and make a plan for Chester to go straight from the sale barn to the clinic. That meant less time on the trailer, faster relief, and x-rays scheduled for first thing Monday morning.
Treatment for selenium toxicity usually means removing the horse from selenium-rich sources, providing good nutrition, and supporting the hooves. But the prognosis depends on how advanced the damage is.
The Role of Sulfur
One of the strategies we’ve been advised on is supplementing sulfur, which can help balance out high selenium intake. For cattle, sulfur blocks are often used for this purpose, and you’ll find them at most livestock supply stores in our state.
For horses, the most effective and safest way to add sulfur is usually through MSM (methylsulfonylmethane), an organic, highly bioavailable form of sulfur. MSM supports connective tissues, hooves, and joints, and it’s generally very safe.
Other options include sulfur-containing amino acids like methionine and cysteine, which are common in hoof supplements. Products like Farrier’s Formula® use these building blocks to support hoof growth without adding MSM.
⚠️ A note of caution: too much sulfur from multiple sources can interfere with copper absorption and may actually weaken hooves and joints. If you’re already feeding a hoof supplement with methionine, adding MSM on top may not be the best idea. Always work with your veterinarian or an equine nutritionist to make sure you’re balancing minerals appropriately.
For Chester, MSM will likely be part of his supportive care, but we’ll be monitoring closely to make sure we’re giving him the best chance possible without creating new issues.
Why His Story Matters
In South Dakota, selenium isn’t just a footnote—it’s part of the land. Horses here don’t need extra selenium the way they might in other parts of the country. Awareness can mean the difference between a healthy horse and one who suffers like Chester.
By sharing his story, we hope horse owners everywhere—especially here at home—will take a second look at their feed tags, hay sources, and pastures. And hopefully, fewer horses will end up walking in Chester’s painful footsteps.
📸 Warning: graphic hoof photos below