A Discussion About Selenium and Horses

– by B.Lynne Hoff, B.Sc.Pharm, President Sunglade Ranch

There are a lot of worries in literature about Selenium and how toxic it can be to horses. Selenium poisoning is certainly serious, debilitating and can be fatal.

Since selenium comes from the soil and some plants concentrate selenium, it is difficult to determine how much selenium to include in a feed supplement. For example, because of the lack of topsoil and heavy rains, Vancouver island is extremely low in selenium. The following map that is a general guideline.

Please remember that there can be isolated pockets of high selenium and that mining can sometimes pour mercury and selenium into waterways. If you are downstream from a mining operation, beware. If you live in an area with extremely high selenium, it will be imperative to contact your local vet for information. However, as you can see by the map, most areas are adequate or low in selenium.

Some of the early indications of poisoning is poor hair coat and dry, cracking hooves with sloughing off of the hoof in more chronic cases. However, low selenium can result in white muscle disease which is also fatal.

So, what are safe levels and dangerous levels?

An inactive, average (1100 lb) horse needs about 1-3 mg daily and an active one about 3 to 5 mg daily. Good feed and forage supplies about 0.2 mg to 0.3 mg/kg (2.2 lbs ) of feed. Let’s take an average of 25 lbs (11.3kg) feed per horse per day. So your horse would receive about 3.3 mg selenium per day from ordinary feed/forage which is just about right.

So what is the minimum requirement to avoid deficiency?  

Apparently that is about 1mg per day per horse.  Toxicity can arise at 50 to 500 mg per day per horse for chronic poisoning and 2500 mg per day per horse for acute.

So you can see that there actually is a pretty big range between deficiency and toxicity. However, because the ranges are SO much more spread out for other minerals, warnings about selenium are rampant in the literature.

BioEquine supplies 0.6mg Selenium per daily (30 gm) dose. We have carefully chosen that middle ground. It is enough to stave off complications in areas that have absolutely NO selenium but not enough to add toxicity to areas that are on the high side.

Interestingly, the silica DE base that we use in BIoEquine is a toxin binder and we had an extremely interesting scenerio in Idaho with a herd of cattle that were being poisoned by Flourides in their pasture waterway. The local vets could not figure out what was happening! Luckily the owner tried some BIoEquine on the cattle that she had on hand for her horses. The herd, that was extremely debilitated (some were eating on their knees because their feet were so sore), recovered in two weeks!  That made us suspect some sort of poisoning.  The creek was tested, and sure enough…too much flouride. They were subsequently moved out of that pasture and are now doing well. So we feel that there is a very good chance that the BioEquine may help guard against selenium poisoning as well!

We advise anyone that thinks they may be in an area of either extreme to contact the local veterinarian. The best is to talk to the old horsemen in your area. THEY will be the local experts and will appreciate your concern and respect.