8 ALL ABOUT FEED Volume 23, No. 8, 2015

Organic selenium is all about selenomethionine

F e e d a d d i t i v e s

Selenium is an essential trace element and plays a crucial role in maintaining an optimal health status. Selenium sources can be categorised as organic or inorganic. Here we delve deeper into organic selenium and, more specifically, selenomethionine.

By Marc Rovers, Orffa, the Netherlands

S elenium is a key nutrient in animal nutrition and is crucial for an optimal antioxidant status and immune function. Selenium in animal diets can be supplied via raw materials or via supplemented selenium. Selenium from feedstuffs is predomi-

nantly present in the form of L-selenomethionine, which is the natural form of selenium in plant protein and animal tissue. The supplemented selenium can be either in an organic or an inorganic form. Organic selenium has an important benefit compared with inorganic selenium due to the fact that selenomethionine, the effective organic part of

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ALL ABOUT FEED Volume 23, No. 8, 2015 9

Other Se compounds• Selenocysteine (Se-Cys)• Other (organic) Se intermediates• Inorganic Se

L-SelenomethionineE�ective organic Se

Incorporation in animal proteins• Se status, storage in tissue, Se reverve for later mobilisation (protein turnover)• Se transfer to offspring• Se enrichment of animal products, meat, milk, egg

Seleno enzymes• Glutathion peroxidase• Antioxidant role• Immunity

ExcretionVia breathand urine

de novoSe-Cys

H2SeSelenide

Se in the metabolismSe in the diet

0%1 2 3 4 5 6 7 1 2 3 4

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Se as SeMet, % of total Se

5 6 78 1 2 3 4 5 6 7 8 1 1 1 1

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organic selenium, is utilised by the body as an amino acid (in same way as methionine) and is built into animal pro-tein tissue. Via this metabolism, organic selenium in the form of L-selenomethionine is able to build up selenium reserves in the body, which ensures a good selenium and antioxidant sta-tus at all times and secures the efficient transfer of selenium to offspring via the placenta, milk and eggs. Selenomethionine in metabolismIn the metabolism there is a difference between selenome-thionine and all other forms of selenium. Traditionally, organic selenium was supplied via selenium-enriched yeast. Selenium yeast consists of up to 98% organic selenium, but not all of this organic selenium is in the form of selenome-thionine. Currently, EU legislation mentions that 63% of the selenium in selenium yeast should be in the form of sele-nomethionine; more recent authorisations refer to 70%. The remaining part is in the form of selenocysteine, other (organic) intermediates or inorganic selenium. The differ-ence between selenomethionine and all other forms of sele-nium in the metabolism, as far as actual knowledge is con-cerned, is explained in Figure 1. All selenium compounds are recognised as a selenium supply in the metabolism and all can be used for selenoprotein (selenoenzymes) synthesis. Besides this general pathway, selenomethionine can be built

Laying hens that received the new form of organic selenium in the diet were able to deposit more

selenium in the eggs than laying hens that received inorganic selenium or selenized yeast.

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Figure 2 – Selenium in form of selenomethionine, % of total selenium in commercial selenised yeast samples.

Figure 1- Selenomethionine and other selenium compounds in the metabolism.

into body proteins instead of methionine. Via this specific pathway, selenomethionine is able to build up selenium reserves in the body and is able to transfer selenium to the offspring via the placenta, milk or eggs. The selenium reserve in the body can be mobilised for later selenoprotein synthesis. An adequate selenium reserve ensures an optimal selenium and antioxidant status at all times, even in times of stress or low feed intake. However, all other forms of selenium in selenised yeast, such as selenocysteine and other organic selenium intermediates, are reduced to hydro-gen selenide and then utilised for de novo selenocys-teine and selenoprotein biosynthesis. Dietary selenocysteine is not used directly for selenoprotein synthesis, but is first reduced to selenide, from which new de novo selenocysteine is formed. Inorganic selenium is also reduced to selenide and then is utilised for selenocysteine and selenoprotein

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Sodium seleniteSelenized yeastExcential Selenium4000

Stability of L-SeMet in vitamin mineral premix

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synthesis. Thus, the remaining part of selenium in selenized yeast (selenocysteine and (organic) selenium intermediates) follows the same pathway as inorganic selenium and is con-sidered to be not more effective than inorganic selenium in the metabolism. L-selenomethionine is considered as meta-bolically effective organic selenium.

Level of selenomethionine in selenised yeastSeveral producers offer selenium yeast products for animal nutrition. To evaluate the quality of selenised yeast prod-ucts, it is important to check the selenomethionine level in these products. A market survey was set up to check the selenomethionine content in commercially available sele-nised yeast products in the market. In total, 28 samples were collected from seven different producers. The samples were analysed for total selenium and for selenium in the form of selenomethionine. The survey was set up by Orffa in co-operation with the lab of CODA CERVA (Tervuren, Belgium). The analysis method applied is specific for se-lenomethionine and is based on HPLC ICP MS after enzy-matic extraction. The results are shown in Figure 2. From this market survey, it can be concluded that there is a major variation in the level of Se in the form of selenomethionine between different commercial samples of selenised yeast. The overview shows differences between producers, as well as variations between batches of the same producer. This variation can also be found in scientific literature and has been confirmed in other commercial reviews. The level of selenomethionine is an important quality parameter. Nutritionists are inceasingly aware of this and request guar-antees from their suppliers. New generation of organic seleniumRecently a new type of organic selenium was introduced into the animal nutrition market. This product tackles the problem of variable concentration. The product* consist of L-selenomethionine and is considered 100% digestible. All selenium in the product is digestible and metabolically effective organic selenium. Several animal trials show the benefit of this new generation of organic selenium. For example, Figure 3 shows the results of a trial in laying hens in which different sources and dosages of selenium were evaluated. Laying hens that received selenised yeast in the diet were able to deposit more selenium in the eggs than laying hens that received inorganic selenium. Moreover, the group that received a diet supplemented with L-Selenomethionine* had the highest selenium in the eggs, which was significantly higher than the selenized yeast. This trial demonstrates the higher selenium transfer of the new generation of organic selenium compared with selenised yeast. Similar to these results in laying hens, a second study in dairy cows showed the same trends (Vandaele ea, 2014), whereby L-Selenomethionine resulted in a higher transfer of selenium versus seleniumyeast and inorganic selenium resulted in the lowest response. Stability in feed and premixesIn order to be efficient in the animal, a feed component should be stable throughout the feed production process.

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Figure 3 - Selenium in eggs related to the selenium source and dosage in feed (Delezie et al, 2014).

Figure 4 - Stability of L-SeMet in vitamin mineral premix.

This means both in feed production and in premix produc-tion. The stability of L-SeMet has been investigated exten-sively and it has been concluded that the product is stable in pure form, mixed in a vitamin/mineral premix and in com-plete feed. It has to be noted that, for the analysis of SeMet in a high concentrated vitamin/mineral premix, a specific analytical protocol for the determination of SeMet should be applied. Not applying the correct protocol may lead to misinterpreting the results. If the correct protocol is used, the SeMet in premixes can be determined correctly. Figure 4 shows the results of a stability test of L-selenomethionine in a vitamin/mineral premix and shows that the product is sta-ble during storage of the premix. ConclusionWith the introduction of a new form of organic selenium, new opportunities arise for animal nutritionists. The new generation of organic selenium shows no variation in con-centration and guarantees all its selenium in a digestible and highly effective organic form. It allows a more standardised amount of active ingredient (selenomethionine) to be deliv-ered via the diets to the animals.

*Excential Selenium4000

F e e d a d d i t i v e s

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