Feed & Additive Magazine Issue 47 December 2024

ISSUE FOCUS 30 FEED & ADDITIVE MAGAZINE December 2024 thionine is utilized in the body as an amino acid and can be incorporated into body proteins in place of methionine. Through this specific pathway, L-selenomethionine is able to build up selenium reserves in the body, and efficiently transfer selenium to the offspring through colostrum and milk. The greater retention of L-selenomethionine in animal protein, provides a safe reserve of selenium in the animals’ body which ensures the future selenium supply. During protein turnover, stored L-selenomethionine will be released and can be used for selenoenzyme synthesis at any time. Use of L-selenomethionine can be the solution to mitigate the risk for lower selenium availability in the animal, especially when selenium (bio)availability from the diet is low due to variation in the raw materials and/ or influenced by the production process. L-SELENOMETHIONINE FROM ORGANIC SOURCES Both selenized yeast and pure L-selenomethionine sources contain L-selenomethionine, however they differ in concentration of L-selenomethionine within the product. Selenium yeast consists of up to 98% organic selenium, though not all of this organic selenium is in the form of L-selenomethionine. According to EU legislation, 63% of the selenium in selenized yeast should be in the form of L-selenomethionine. The remaining part of the selenium is in the form of selenocysteine, other (organic) intermediates or inorganic selenium. In the metabolism (Figure 4), selenocysteine and other (organic) selenium intermediates are reduced to hydrogen selenide and then utilized for the novo- selenocysteine and selenoenzyme biosynthesis. Thus, the remaining selenium in the selenized yeast (<37%) follows the same pathway as inorganic sodium selenite. In contrast, 100% of a pure L-selenomethionine source can be used for both pathways in the metabolism. Selenium deposition, and thereby the difference between dietary selenium sources, can be measured in milk and muscle tissue. Although no comparative Control (0,05ppm) Sodium selenite (0,33 ppm) SeYeast (0,32 ppm) Excential Selenium4000 (0,32 ppm) Se deposition in muscle tissue (mg/kg) Se deposition (mg/kg) 1 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 cd 0 6 10 ab b a b c d c c week Figure 5. The safe deposit of selenium in the animal depends on the dietary selenium source (adapted from Falk et al, 2018)

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