Selenium Toxicosis Average Cost

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What are Selenium Toxicosis?

A horse that weighs 1,000 pounds should only have 20 mg of selenium per day. Most horses get more than enough selenium from their regular diet. Adding more selenium in supplement form per day can cause signs of toxicity. 

On the other hand, a deficiency in selenium can be very detrimental to a horse. Before adding any supplement to your horse’s diet, be sure to consult your veterinarian.

Selenium toxicosis in horses occurs when a horse’s diet has been over-supplemented with vitamins and minerals. Selenium, a mineral that protects cells from damage, can be toxic to horses if given too much in their diet. Those horses suffering from chronic selenium toxicity are diagnosed with alkali disease.

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Symptoms of Selenium Toxicosis in Horses

The severity of the symptoms of selenium toxicosis will vary depending on the amount of selenium in their body and the length of time the selenium has been building up in their system. If you notice any of these changes to your horse, contact your veterinarian for an appointment. 

  • Anemic
  • Lack of vitality
  • Emaciated 
  • Blindness 
  • Lameness due to founder
  • Anorexic
  • Rough hair or coat
  • Respiratory failure
  • Long hairs of the mane and tail break off
  • Abnormal growth and structure of the hooves
  • Cracking of the hoof wall at the coronary band
  • Long, deformed hooves that will turn upwards at the end
  • Reduced fertility
  • Liver cirrhosis
  • Myocardial necrosis
  • Twisted legs in foals

Causes of Selenium Toxicosis in Horses

The obvious cause of selenium toxicosis is exposure to high levels of selenium. Long term exposure can lead to chronic selenium toxicity and can lead to death. Most horses receive enough selenium in their normal diet; however, well meaning owners will give supplements containing selenium. These supplements are many times unnecessary and will cause selenium levels to build up within your horse’s system causing severe health problems that could leave long term damage to your horse. 

Research your horse’s feed and know the selenium content before adding supplements that could cause alkali disease that cannot be reversed.

Diagnosis of Selenium Toxicosis in Horses

Diagnosing selenium toxicosis in horses can be difficult for your veterinarian. They will begin by performing a full physical examination of your horse. Your veterinarian will need to know your horse’s feeding schedule and source, along with any additional supplements that you may be giving. 

The clinical symptoms along with laboratory results will confirm the presence of high levels of selenium within the body. Your veterinarian will take tissue samples, blood samples, and a urine sample to send to the laboratory for analysis. Tissue selenium content is the best way to diagnose selenium toxicosis since organic chemical forms of selenium have a greater bioavailability and stay in the tissues for a longer amount of time.

Treatment of Selenium Toxicosis in Horses

Once your veterinarian has definitively diagnosed selenium toxicosis in your horse, a treatment plan will be developed. There is no specific treatment for selenium toxicosis in horses; the treatment plan is on a case by case basis. 

The first step is to eliminate the source of the selenium. This will stop any ongoing poisoning and allow the symptoms to be treated without compounding the issue with higher levels of selenium being ingested. 

Supportive care will also be recommended. This will include having your horse hospitalized so they have constant care during their time of duress. Intravenous fluids will be given to re-hydrate your horse. Oxygen support may also be necessary if your horse is experiencing respiratory distress. 

Treating the symptoms will also be necessary to limit the amount of long term effects of selenium toxicosis. If your horse’s hooves are brittle or cracking, your veterinarian will suggest that an experienced farrier help treat your horse’s condition. Without proper treatment, your horse’s hoof may actually slough off and expose the laminae. This will cause your horse extreme pain and permanent lameness. 

Your veterinarian may suggest a diet that will counteract the effects of the selenium toxicity within your horse. This diet should include high protein, linseed oil meal, silver, arsenic, sulfur, copper, cadmium and mercury. All of these have been proven to reduce selenium toxicity in horses.

Recovery of Selenium Toxicosis in Horses

Depending on the severity of the selenium toxicosis, your horse may be able to make a full recovery. If your horse’s hooves have been compromised, it will take extensive care to try to rebuild the hoof to where your horse can function as a pasture horse.

Each year, you should have your horse’s pasture tested for selenium to ensure that the pasture does not have a high selenium content. Also, keep informed about your horse’s feed and the amount of selenium that is contained in each serving. If you feel that your horse needs a selenium supplement, consult your veterinarian before giving any new supplements.

Selenium Toxicosis Questions and Advice from Veterinary Professionals

8 Years
Mild condition
0 found helpful
Mild condition

Has Symptoms


I have a horse that had a spinal Vit E tap that came out borderline low, his Vit E levels are low as well when not supplemented.
However I found out his selenium levels are too high, 34 ug/dl and they should be below 24 ug/dl.
I am worried about toxicity, but don't know how to bring the Se bloodlevels down.
He gets no supplemental Se, only fed 6lbs of Triple Crown Senior feed and local east coast hay, which presumably is low in Se.
Over winter he did get some western timothy hay, but this has now been stopped.

I'd love to supplement him with the above suggestions of silver, arsenic, sulfur, copper, cadmium and mercury.
Where could I order those?
And is MSM a good source of sulfur, if so how much to supplement? 10.000mg/daily or more?

Any suggestions for a horse feed not containing added Se?

Thank you kindly,

Dr. Michele King, DVM
Dr. Michele King, DVM
1611 Recommendations
There are many details about RG that I do not know, and cannot responsibly comment on, unfortunately. Since he has a condition that does require frequent monitoring, it would be best to discuss any supplements or changes with your veterinarian, as they know him and can see him.

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