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by Phileo- Lessafre

n 1817, selenium (Se) was isolated for the first time by Berzelius. At that time little was known about its biological function, until its nutritional requirement was revealed about 140 years later by Schwarz and Foltz in 1957 (Mehdi et al., 2013). Since then, Se has been recognised as an essential trace element and its supplementation to farm animals has become a common practice worldwide, as Se deficiency increases susceptibility to various diseases and decreases productive and reproductive performances of farm animals (Lyons et al., 2007). The essence of Se to exert its positive effects lies in the construction of the 21st amino acid selenocysteine (SeCys). SeCys can be found at the active site of a wide range of proteins, also called selenoproteins, which play important roles in the antioxidant defense and immune function. One of the most importent selenoproteins identified is glutathione peroxidase (GPx), which functions as an antioxidant by directly reducing hydrogen peroxides (H2O2) and phospholipase A2 cleaved lipid hydroperoxides and thus reducing the level of lipid and protein oxidation in the cell (Brown and Arthur, 2001).

Selenium metabolism in yeast and animals

Nowadays, farm animals can be supplemented with Se under an inorganic or an organic form. These inorganic forms are mainly mineral salts such as sodium selenite (SS) or selenate, while organic forms can be found as synthetic selenomethionine (SeMet) or as selenized yeasts rich in natural Se components. These selenized yeasts can be produced in different ways, but the highly consistent selenized yeast ‘Selsaf®’ is obtained due to the specific cultivation of a proprietary Saccharomyces cerevisiae (CNCM I-3399) strain on a medium enriched with SS. During the growth of the yeast, SS will be transformed to hydrogen selenide (H2Se). H2Se is an intermediate metabolite used by the yeast to synthetise different organic selenomolecules such as the seleno amino acids selenomethionine (SeMet) and selenocysteine (SeCys), but also many other seleno-active components (Kieliszek et al. 2015). Consequently, due to the standardised production procedure, Selsaf® contains 2 natural organic Se fractions which are easily absorbed in the animals’ intestine I) 63 percent SeMet and II) 36 percent SeCys and other active selenocomponents. In the first fraction, SeMet closely 66 | July 2016 - Milling and Grain

resemblances the amino acid methionine (Met), as the only difference between the 2 is the substitution of the sulfur atom by a selenium atom in SeMet. This will lead to the non-specific incorporation of SeMet in the animal’s body proteins. As such, a pool of Se under the form of SeMet is created in animal proteins found in eggs and milk, leading an efficient transfer of Se to offspring. Additionally, SeMet is also incorporated and stored in the muscles where it can be addressed in stressful times. Under stress conditions, SeMet will be released from this reserve pool in the muscle due to catabolism and liberated SeMet can be converted to H2Se for the construction of animal SeCys in the selenoenzymes (Schrauzer, 2000).

Figure 1: activation of GPx selenoenzymes by Selsaf® in comparison with control group and sodium selenite

Figure 2; antiradical capacity of whole blood from beef cattle supplemented with Selsaf® in comparison with sodium selenite

Figure 3; BHV1 antibody titers in serum from beef cattle supplemented with selsaf® or SS

Figure 4; serum bactericide activity from beef cattle supplemented with selsaf® in comparison with sodium selenite

Figure 5; % of animals suffering from MRD (A) and ADWG (B) of beef cattle supplemented with Selsaf® compared to SS

JUL 2016 - Milling and Grain magazine  
JUL 2016 - Milling and Grain magazine