Selenium Deficiency in Horses, Signs and Treatment

Last year, my best friend’s horse was suffering from selenium deficiency. It got so severe that she and her horse had to go through a lot to deal with the situation. I’m not a vet and have never worked with a vet but have kept horses for almost a decade. The information I am about to provide below is gathered from years of experience.

Selenium is an essential mineral that is freely found in the soil, groundwater, and plants. Horses generally don’t need a huge amount of selenium per day to live a balanced, healthy life but that doesn’t mean they can not suffer from selenium deficiency. 

The horse owners usually don’t have to look for a selenium supplement as the horse is already consuming it naturally. You may expect selenium deficiency in horses when the hay and the groundwater they are consuming contains a little or no amount of selenium at all.

Selenium deficiency is rare but it can lead to death. So, even mild selenium deficiency should go unnoticed or untreated. Early detection does not just minimize the chances of adding selenium supplements but also reduces the risk of death to a large extent.

My intentions were not to scare you, as I’m about to discuss what are the causes and symptoms of Selenium deficiency and how it can be treated. So, let’s begin with;

What causes selenium deficiency in horses?

Selenium is mostly consumed naturally through hay, grass, and haylage. If the soil these contents are growing in contains a little or insufficient amount of selenium, the horses get selenium-deficient over time as their food is not fulfilling the selenium need. So it wouldn’t be wrong to say that a feed low in selenium causes selenium deficiency in horses.

What are the signs of selenium deficiency?

Selenium deficiency drops several signs of its severity in a short period. All these signs are noticeable but sometimes we are just too naive to identify the problem. The most common symptoms of selenium deficiency are;

  • Sore muscles
  • Poor performance
  • Trembling or Muscle Spasms
  • Stiff gait
  • Tying up
  • Respiratory distress
  • Difficulty in suckling
  • Impaired movement
  • Poor fertility 
  • Poor coat and hoof quality

There would probably be a lot more to tell that the horse is selenium deficient but these are the major noticeable signs of mild selenium deficiency. The signs and symptoms of severe selenium deficiency are;

  • Difficulty in chewing and swallowing
  • White muscle disease and muscle deterioration
  • Heart failure and death

Can selenium deficiency Treatment

Mild to moderate selenium deficiency can be treated without any selenium supplement. It can be cured by adding a noticeable amount of selenium-rich food to the horse’s daily diet. But the severe selenium deficiency may or may not be cured, it “actually” depends on the horse’s condition and lifestyle.

According to science direct Severe selenium deficiency is vastly treated by combining selenium-rich foods and vet prescribed selenium supplements.You can feed lentils,cachew, and bannas to horses as a treatment.

Hay, grains, pasture, and commercial feeds are the only source of selenium. Arranging horse food from the soil that is rich in selenium would fill some part of the total selenium gap. Moderate or mild selenium deficiency should be discussed with the vet as it grew up to a life threat.

Now you know the basics; causes, signs, and cure for selenium deficiency. Half knowledge is dangerous so let’s dig deep into this alarming topic.

So, what else do you need to know about selenium consumption and deficiency?

Selenium consumption and deficiency are rarely discussed as selenium is being consumed naturally and the horses seldom get selenium deficient. So, there is a lot you need to know about this essential trace mineral that horses need in a small amount.

Why do horses need selenium?

Adequate selenium in the horse’s body helps in maintaining a healthy muscular, thyroid, and immune system. Moreover, it also plays an important role in decreasing oxidative stress. This antioxidant when combined with vitamin E prevents free radicals from damaging healthy cells.

How much selenium does a horse need in a day?

The selenium consumption should be kept under 6 mg a day to cut short the chances of selenium deficiency and toxicity. Both over and underdose of selenium may lead to death so on average four to five mg selenium a day keeps the vet away.

If you want me to get more specific about the selenium intake I would say an average 500 kg horses need 1 mg of selenium per day (minimum) for the better functioning of their body but if 2 to 3 mg of selenium can be arranged it would help in building stronger muscles and immune system. 

Going above the digit “6” (mg) would be harmful to this poor creature. As it’s easier to get selenium toxicity than to become selenium deficient because they are already consuming it in their daily meals.

How do you know that your horse needs an additional selenium supplement?

To get the accurate answer to the question, how do you know that your horse needs an additional selenium supplement? you need to check if the feed your horse is consuming is coming from a selenium-deficient area or not. If it is confirmed by ingentaconnect the soil is selenium deficient it’s time to either change the supplier or look for a selenium supplement.

The first thing you need to consider is how much selenium your horse is consuming these days? The rest of the total selenium requirement can then be fulfilled through vet prescribed selenium supplements. For example, if the horse is consuming 1 mg of selenium every day then you need to arrange 2 to 3 mg of selenium additionally.

How is selenium deficiency tested?

Selenium deficiency is visible through its signs and symptoms but is there a way to confirm if the horse is “actually” suffering from selenium deficiency?

Yes, it can be checked through a blood test. Hair, plasma, serum, and tissues can also be tested for better confirmation.

How long does it take to be treated?

It’s a slow process so it can not be cured in a matter of days or weeks. It roughly takes a year or 6 months minimum to be treated. So, for such a long period you have to bear the horse’s poor health and performance.

Bonus Tip

Selenium Deficiency signs

Selenium toxicity in Horses

In between fulfilling the selenium deficiency, there are some solid chances that your horse can suffer from short term selenium toxicity.

It’s not life-threatening but at this stage, selenium-rich foods should be avoided for a short period. The common signs of short term selenium toxicity are nervousness, fear, depression, diarrhoea, muscular weakness, respiratory distress, and decreased appetite. So, watch out for these signs for your horse’s safety.

What I have learned all these years is that “don’t be a doctor” whenever you see your pet behaving abnormally. Take and get them checked thoroughly as they can not speak or sometimes even express what’s bothering them. A vet only knows what’s going wrong inside that poor thing.

Selenium deficiency and toxicity can occur at any time as selenium is consumed through food. It’s better to get the horse’s blood annually tested to see if the horse is doing okay.

Frequently Asked Questions

Is selenium deficiency common in horses?

Selenium deficiency is common in some parts of the world but selenium toxicity is more common than the said disease.

How does selenium deficiency occur?

Selenium deficiency occurs when the horse is living on the hay, grass, or pasture that is coming from a selenium-deficient soil or the food is not fulfilling the total selenium requirement(3 to 4 mg per day)of the horse.

What are the signs of selenium deficiency?

There are many signs of selenium deficiency but the common ones are sore muscles, poor performance, trembling or muscle spasms, stiff gait, tying up, respiratory distress, difficulty in suckling, impaired movement, poor fertility, and poor coat, and hoof quality.

How much selenium does a horse need in a day?

The horse needs on average, 3 to 4 mg of selenium every day to live a balanced healthy life. Even if the horses are consuming at least 1mg of selenium every day they would still not get selenium deficient.

How long does it take to cure the selenium deficiency in horses?

Depending upon the situation, it usually takes months or even a year to overcome this life-threatening disease. 

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Selenium deficiency is rare but life-threatening. Horses get selenium-deficient when the hay, grass, and pasture they are living on is being grown in selenium-deficient soils. The common noticeable symptoms of selenium deficiency are sore muscles, poor performance, trembling or Muscle Spasms, stiff gait, tying up, respiratory distress, difficulty in suckling, and impaired movement, etc.

The selenium deficiency is curable and sometimes incurable (if the horse owner shows reckless behaviour). It can be cured within a year by adding selenium-rich foods and selenium supplements to the horse’s diet. Selenium deficiency can only be confirmed through a blood, plasma, hair, and serum test.


Hi, I am Waqar and active in the horse world since 2012. I have MSc (Hons) in Agriculture from the University of Agriculture Faisalabad. I love to solve equine health care issues and note down in the form of research papers. I have written hundreds of equine health care, accessories, names, and history-related blogs. My equine related work is watering a lot of horse-related magazines and blogs.

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