What is organic selenium?
In plants and yeast, selenium is naturally built into the amino acid methionine, giving selenomethionine (and smaller amounts of selenocysteine). Organic selenium feed additives aim to supply selenium in this form.
Selenomethionine is absorbed through amino acid transport pathways. The body cannot distinguish it from methionine, so part of it is incorporated non-specifically into body proteins such as muscle, where it forms a selenium reserve that can be mobilised later. The rest is converted into the selenium-dependent enzymes, just as selenium from selenite is.
What does organic selenium do in animal feed?
- Provides selenium for glutathione peroxidases and other selenoproteins that support antioxidant defence, thyroid function, immunity and fertility.
- Builds body selenium reserves that can help animals through periods of higher need, such as calving, farrowing, hatching or heat stress.
- Increases selenium transfer to eggs, milk, colostrum and the foetus, supporting the selenium status of chicks, piglets, calves and lambs.
- Raises the selenium content of meat, eggs and milk more effectively than inorganic selenium.
- Is non-reactive in the premix and does not act as an oxidising agent, unlike selenite.
Forms of organic selenium
- Selenium yeast: Saccharomyces cerevisiae grown on a selenium-enriched medium; most of its selenium is selenomethionine, but the proportion varies between products.
- L-selenomethionine: a synthetic, chemically defined form, offered for example as zinc-L-selenomethionine, with a known selenomethionine content.
- Hydroxy-selenomethionine (2-hydroxy-4-methylselenobutanoic acid, HMSeBA): a synthetic, chemically defined precursor that is converted into selenomethionine in the body.
- Many premixes combine an organic form with sodium selenite to balance cost and selenium deposition.
How is organic selenium used in formulation?
Organic selenium is usually considered where reserves and transfer to offspring or products matter most: breeder and layer feeds, sow diets, dairy cows in the transition period, and calf and lamb feeds. Many nutritionists replace part or all of the selenite with an organic form rather than increasing total selenium.
The total selenium level is regulated because selenium has a narrow safety margin. In the EU, total selenium in complete feed is limited to 0.5 mg/kg (at 12% moisture), and the amount added as organic selenium is capped separately. Local regulations and the product label always prevail.
Quality criteria
- Guaranteed total selenium content, verified by analysis.
- Selenium speciation: the proportion of selenium present as selenomethionine, and for selenium yeast the share of inorganic selenium left in the product.
- Batch-to-batch consistency, especially for yeast-based products.
- Homogeneity and flowability for accurate mixing at very low inclusion rates.
- Certificate of analysis (CoA) and lot traceability.
CTF Premix and organic selenium
Organic selenium sources such as selenium yeast or hydroxy-selenomethionine can be included in CTF Premix's mineral and vitamin-mineral premixes according to the customer's formulation, alone or combined with sodium selenite. Premixes are produced at our Ankara facility under ISO 9001:2015 and GMP, with micro-ingredient mixing procedures, and every lot has a certificate of analysis and lot traceability.
This page is for general information. Inclusion rates and product choice should be decided with a nutritionist, taking into account the species, the feed formulation and the applicable regulations.