Feed additives

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The benefits gained from new selenium

Organic selenium becomes more effective as new pure selenium molecules hit the market. The antioxidant seleno-hydroxy-methionine is able to target the right spot in the animal and release 100% pure selenium effectively.

By Pierre-André Geraert, Adisseo, France

Oxidative stress – as a result of free radicals in the animals body – should be prevented as this type of stress speeds up the ageing process or decreases metabolic efficiency. It also can have major effects on productive and reproductive performance of farm animals and poultry. Hatching, weaning and the first phases of life are challenging periods for young animals resulting very often in this 'oxidative stress', meaning the animals are more susceptible to diseases. To prevent this, natural antioxidant defences have been developed in living organisms, such as glutathione, glutathione peroxidase, superoxide dismutase, catalase as well as polyphenols, carotenoids, tocopherol and ascorbate. In most cases, oxidative stress has been appreciated through its effect on lipid oxidation. All cells are surrounded by a bi-layer of phospholipids. Thus reducing lipid oxidation will help to maintain cell integrity and thus resistance to aggressive environment. However, proteins are also targets for ROS, even a mild oxidation of an enzyme will lead to lose of its functionality particularly through cysteine oxidation leading to potential deleterious effects on muscle development and more practically meat quality. An antioxidant that can be supplemented via the feed and involved in both lipid and protein antioxidation is selenium. Most supplementation of selenium (Se) is performed through its inorganic forms as sodium selenite (Se IV) or selenate (Se VI) while organic forms are mainly represented by  selenised yeasts containing seleno-methionine. Intermediate forms are represented by the proteinates which are combination of mineral Se associated with organic proteic structures to presumably increase their bioavailability. As selenium is a metalloid, it cannot be chelated. The only so-called chelate available on the market is a chelate of L-selenomethionine with Zn thus chelating methionine and Zn and not selenium.

Selenium metalloid

But what is selenium? Selenium is present within at least 25 proteins, named selenoproteins. The first one, Glutathione peroxidase, catalyses the oxidation of glutathione to scavenge the free radicals.  In those selenoproteins, Selenium is present in the form of an amino acid, selenocysteine (the 21st amino acid), which is the active component, it has its specific codon UGA to be synthetized when required by the metabolism. Being highly reactive, Se-Cys is only synthetised when needed by the organism, there is no storage of this amino acid. For a given seleno-protein, replacing chemically Se-Cys by Cys, will drastically reduce its antioxidant potential: it is indeed the Se metalloid within Se-Cys that gives its strong anti-oxidant potential. All forms of selenium supplied via the feed (organic and inorganic) have to be converted into hydrogen selenide to generate the selenophosphate for the synthesis of Se-Cys.

100% efficient

In order to refine the antioxidant solutions, it is thus important to have a pure source of efficient selenium that can directly be used by the organism either for Se-Cys synthesis or to increase the selenium pool as Se-Met in the various tissues. A  selenised yeast contains about 98% organic selenium, however only a limited and variable amount is in the form of seleno-methionine and thus can be absorbed and deposited in the body proteins. All other organic Se-compounds will have to be fully broken down to hydrogen selenide to be used by the metabolism as inorganic forms of selenium. Moreover, seleno-yeasts exhibit rather high variability in their selenomethionine content currently around 55-65% as well as its localisation, in the soluble yeast fraction or linked to the cell wall, and thus affecting its bioavailability. Using a  selenised yeast to supply a specific and guaranteed level of organic selenium might thus be not so easy. Animal nutrition company Adisseo has developed a new chemical form HMseBA, Selisseo based on hydroxymethionine or methionine hydroxyanalogue where sulphur has been replaced by selenium (Figure 1). HMSeBA is fully metabolised into selenomethionine and Se-Cys in the animal 's digestive system. This HMSeBA is obtained through a specific chemical process that guarantees the delivery of a pure product. When comparing HMSeBA to Se-yeasts, tissue Se deposition appeared further increased by more than 40% in broilers (Briens et al. 2013, 2014 Figure 2), in layers (Jlali et al., 2013) and in swine (Jlali et al., 2014). Comparing HMSeBA, Se-yeast and pure L-Se-Met shows that the difference is due to the concentration of active product: the seleno-methionine (Figure 3). A recent paper published at the last EggMeat 2013 symposium in Italy has demonstrated that Se-yeast efficiency can only be compared on their Se-Met content even for the same total Se level. Thus HMSeBA has 100% efficiency to increase the Se-Met deposited in the body compared to Se-yeasts containing about 55-65% Se-Met.

More Se available for antioxidant purpose

Recent trials have shown that feeding HMSeBA will not only increase the total Se deposited and the Se-Met content of muscles but also the Se-Cys content of metabolic tissues as well as muscle tissues (Figure 4). As hydroxymethionine  (HMTBA) has been shown to be significantly more trans-sulfurated into Cys than methionine, HMSeBA appeared thus to have the double benefit to increase the circulating and tissue content in Se-Cys incorporated into effective selenoproteins as well as enhancing the deposition of Se as Se-Met in tissues to enhance the potential reserve of Se which will be available for antioxidant purpose under stressful situations.

Based on hydroxymethionine (HMTBA) chemical structure, the HMSeBA benefits of its stability. Indeed thermal treated diets as used in breeders or extruded diets as pet foods or aquafeeds have been performed and showed 100% recovery up to 130°C and 130 bars. Feeding young chicks with heat treated diets containing HMSeBA further demonstrated the full bioavailability and stability of this new form or organic selenium. Moreover, HMSeBA is fully soluble in water which is not the case of selenomethionine, and such an advantage guarantee a complete mixing with feed ingredients and as a pure molecule will also be fully absorbed even by the young animals. Anti-oxidant potential of hydroxy-methionine has largely been demonstrated through better performance under oxidative stress (e.g. heat stress, dietary imblances) or reduced meat oxidation through its enhanced trans-sulfuration into cysteine. Seleno-hydroxymethionine thus combine 100% efficiency with an anti-oxidant potential which cannot be reach by other forms of Se.

Adisseo's organic selenium source (Selisseo®) received a market authorisation by the European Commission in May 2013 for its use as feed additive in all animal species.

[Source: AllAboutFeed magazine Vol 22 nr 5, 2014]


The complementarity of antioxidants

Cellular antioxidant mechanisms should be understood as cooperative systems between the natural defences such as glutathione and the enzymes (SOD, catalase..), and the dietary supplied : vitamin E, selenium. No antagonism between antioxidants has been demonstrated so far, rather savings of vitamin E with presence of vitamin C, or reducing the involvement of polyphenols when increasing vitamin E or even sparing some vitamin E with organic Se. It is thus more important to determine which antioxidant is the most effective on lipid or protein oxidation regarding the level or origin of oxidative stress in order to better balance the antioxidant solutions.

Pierre-André Geraert

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