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Selenium Status in HorsesBy Kentucky Equine Research Staff · September 29, 2016

Finding just the right balance of nutrients can be challenging for horse owners. Take selenium, for example. Too much selenium causes alkali disease, or seleniosis, while too little may cause muscle problems or white muscle disease. But how do you know where your horse stands on the selenium front?

“According to a presentation at this year’s Australasian Equine Science Symposium, some New Zealand horses maintained on pasture had selenium blood levels below the laboratory’s normal limit but appeared completely healthy,” relayed Kathleen Crandell, Ph.D., an equine nutritionist for Kentucky Equine Research (KER).

Many parts of the world, including regions of the United States and New Zealand have low soil selenium levels. This translates into reduced levels in forage, which is the primary source of selenium for horses maintained on pasture or fed hay-based diets.

To determine selenium levels in horses maintained on pasture in New Zealand in healthy, adult horses, Erica Gee, B.V.Sc., Ph.D., a senior lecturer at Massey University, and colleagues measured monthly selenium levels for one year. They found:

  • All horses had low blood selenium concentrations over the study period. Average blood selenium levels were 342 nanomoles/liter, which was approximately 5-10 times lower than the normal levels;
  • All horses appeared healthy during the study period despite those low selenium levels; and
  • The levels of selenium in pastures varied from month to month, and supplemental hay was also low in selenium.

According to the researchers, it is possible that dietary vitamin E levels in green pasture may protect horses against the low dietary selenium obtained on pasture and forage because the two nutrients are known to compensate for each other in times of low supply.

One point to ponder: the “clinically normal” appearance of the horses included in the study may not be a sufficient measure of what damage may be occurring on a cellular level from lack of selenium, particularly on a long-term basis.

“More in-depth studies on immune function and muscular integrity are needed to determine whether there are truly no detrimental effects of low selenium intakes in horses,” advised Crandell.

Gee assures us research in this field is ongoing.

To combat potential dietary deficiencies in horses, commercial feeds frequently contain supplemental selenium. As always, consider all forages, feeds, supplements, and mineral blocks when assessing your horse’s overall diet to ensure dangerous nutrient excesses are not reached when attempting to only prevent deficiencies.

KER offers a powdered supplement called Preserve PS, which contains a proven blend of antioxidants, including selenium and vitamin E. In Australia, look for Preserve. Because selenium nutrition is linked with vitamin E, consider a natural vitamin E supplement for all horses that do not have access to fresh forage.  Water-soluble, natural-source vitamin E, such as that found in Nano•E, affords the greatest antioxidant advantages of this nutrient.

*Gee, E.K., C.W. Rogers, and C.F. Bolwell. 2016. Selenium status of unsupplemented adult horses at pasture in the Manawatu region, New Zealand: Preliminary results. Proceedings of the Australasian Equine Science Symposium. Volume 6.