Selenium Yeast vs Sodium Selenite
Selenium is an important mineral for horses. This trace element plays a critical role in reproduction, thyroid hormone metabolism, DNA synthesis and protection from oxidative damage. Horses can get much of their selenium needs through grazing on plants, which use selenium from the soil. However, many areas in the US have selenium-deficient soil, while other areas such as California have selenium-rich soil.
There are two common forms of selenium in horse feeds and supplements: selenium yeast, and sodium selenite (or selenate).
To understand which form is a better choice for your horse, we need to understand the differences between an organic mineral compound and an inorganic mineral compound.
Organic and inorganic compounds
When talking about minerals, “organic” and “inorganic” do not refer to farming methods; minerals are not made by living organisms.
Organic minerals are chelated or bound to carbon-containing substances such as amino acids.
Examples: amino acid chelated calcium, and calcium proteinate.
Inorganic minerals are not chelated or bound to carbon-containing substances.
Examples: calcium carbonate, magnesium oxide.
Sodium selenite can be toxic if too much is consumed. The toxicity of sodium selenite may be related to its inorganic chemical form. Selenium toxicity from consuming too many high-selenium foods, or from living in a selenium-rich area has been reported in humans and livestock.
However, there have been no reported cases of selenium yeast toxicity in animals or humans in the last 40 years.
How plants use inorganic minerals
The grasses in your horse’s pasture take up inorganic minerals from the soil through the plant’s roots. But grass cannot use inorganic minerals just as they are. So, in its sprouting stages, the plant frees amino acids and binds them to the mineral in a process known as chelation. Now, the inorganic mineral is usable by the plant, and considered organic.
Because the conversion of selenium from inorganic to organic happens during the grass sprouting process, the selenium your horse is getting from forage and pasture is the organic form of selenium.
Whole grains can be a source of selenium for humans. Like grasses, grains will take up selenium from the soil during the seed sprouting process, chelate it with free amino acids, and provide organic selenium.
A 2004 review article published in the Journal of Nutrition tackled the issue of bioavailability of selenium yeast, and found that:
1) there was no evidence of toxicity with selenium yeast.
2) the bioavailability of selenium yeast is similar to that of selenium found in wheat (80% absorption).
3) the “increased selenium status is retained for a longer period [compared to inorganic selenium] after supplementation has ceased.” 1
According to the European Food Safety Authority (EFSA): “Despite the higher bioavailability of selenium from organic sources such as selenium-enriched yeast, the toxicity of these organic forms has been shown in a number of studies to be lower than that of inorganic selenite or selenate. This suggests that the increased bioavailability may be counterbalanced by lower toxicity.” 2
An interesting study on weaned piglets with salmonella showed that selenium yeast was more effective in enhancing growth performance and nutrient digestibility compared with sodium selenite.
“Selenium yeast supplementation improved kidney and immune functions and alleviated oxidative stress. […] In conclusion, in this study selenium-enriched yeast was more effective in enhancing nutrient digestibility, and inhibiting inflammation and oxidative stress by inducing the activity of the lymphocytes, expression of antioxidant enzymes and so on.” 3
Sodium selenite is the inorganic form of selenium. The FDA approved sodium selenite in the 1970s for animal and pet foods. It’s made in a lab using the reaction of selenium dioxide with sodium hydroxide.
Sodium selenite (Na2Se03) is described by the American Chemical Society as:
“…a toxic inorganic salt used to neutralize green impurities during the manufacture of colorless glass.” 4
Selenium yeast is produced by fermenting Saccharomyces cerevisiae yeast in a selenium-rich media. The yeast converts the selenium into selenomethionine (selenium bound to the amino acid methionine) accompanied by other bioactive compounds in the yeast.
Some companies use the isolated selenomethionine form in supplements and feeds. However, a 2022 study published in Frontiers in Veterinary Science found that “both selenium yeast and selenomethionine promoted cell viability and attenuated cell apoptosis by regulating the selenoprotein expression and antioxidant capacity but selenium yeast comprehensively exhibited more efficient benefit than that of selenomethionine.”5
Selenium facts to remember
- Selenium is an important micronutrient for horses, and dogs as well.
- The selenium content in foods and forage varies depending on the area where the food is raised or grown, due to regional differences in soil.
This chart from the USDA (2018) shows average selenium content of various foods.
- Sodium selenite is an inorganic mineral. Many companies use sodium selenite in their equine and canine feeds. Supplement companies also use sodium selenite, particularly in multi vitamin/mineral formulations.
- Selenium yeast is an organic form of selenium — the only form of selenium used in BioStar formulas. Plants like grasses and grains convert inorganic selenium to organic selenium using free amino acids to bind to the inorganic mineral molecule. This process increases bioavailability of selenium in the grasses and grains.
- Because of increased bioavailability, selenium yeast is less toxic to humans and animals than sodium selenite.
- TIP: Have your hay and forage tested to know exactly how much selenium your horse is getting.
1 – https://www.cambridge.org/core/services/aop-cambridge-core/content/view/11405388DB9AE553B25275E38B13F9F0/S0007114504002065a.pdf
2 – https://efsa.onlinelibrary.wiley.com/doi/pdf/10.2903/j.efsa.2008.766
3 – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7251790/
4 – https://www.acs.org/molecule-of-the-week/archive/s/sodium-selenite.html
5 – https://www.frontiersin.org/articles/10.3389/fvets.2022.850935/full