Selenium is shown to be an essential element for animal nutrition. Animals are not able to synthesise selenium, and therefore must obtain selenium from their diet. The selenium content of feed and food ingredients varies too greatly to guarantee satisfying animal requirements, therefore selenium must be added to the diet. New Zealand soils are extremely deficient in selenium and due to the fact that selenium is not essential for plant growth (plants grow irrespective of soil selenium status), selenium supplementation of livestock in NZ is critical. Furthermore, despite the fact that selenium intakes have increased over the last 10 years in the NZ human population, the selenium status of New Zealanders is low compared with populations of many other countries and is still considered marginal (Thomson, 2004).
In the 1974, the FDA approved selenium supplements in the form of selenite or selenate for poultry and swine diets. There are now many known inadequacies associated with using inorganic selenium and these include; high risk of toxicity, interactions with other minerals and vitamins, low efficiency of transfer to muscles, eggs and milk and the inability to build and maintain body reserves of selenium.
Over the last 40 years, information has accumulated indicating that naturally-occurring selenium found in plant-based feed ingredients can exist as several seleno-amino acids but the major form of selenium in grains, oilseeds and other important feed ingredients is present as Selenomethionine (Surai, 2006). Organic selenium in the form of selenomethionine is proven to be an effective source of Se for all livestock animals, in comparison to traditional inorganic sodium selenite/selenate forms, primarily because selenium can only be stored in the body as selenomethionine.
After the amino acid selenomethionine is absorbed in the gut, it can be directly incorporated into the animal’s body tissues during protein synthesis in place of a methionine molecule; this replacement has no impact structurally or functionally on the protein. This incorporation of selenomethionine into body proteins creates a reservoir or pool of selenium from which the animal access immediately as/when selenium is required. Under stress conditions, protein catabolism takes place which releases some of the stored selenomethione for conversion and metabolism into selenocysteine and selenoproteins which play fundamental functional roles in antioxidant defences. Other selenoproteins play a role in sperm maturation, immune system activation and thyroid hormone activation.
Recently, Professor Peter Surai of Feed-Food. Ltd (Scotland) visited Palmerston North, New Zealand to address the attendees of the Massey University ‘Advancing Poultry Production Conference’, where it was noted that 2017 marks the 200 year anniversary of the discovery of the element Selenium by chemists Berzelius & Gahn. During his presentation, Professor Surai spoke about the evolution of selenium sources that have historically been available for use in poultry diets over the last 50 years. Surai also introduced the concept of a “Third Generation” selenium supplement, hydroxy-selenomethionine (Selisseo®). Professor Surai concluded his presentation by proposing the idea that building up selenium reserves in the animal’s body in the form of selenomethionine can be likened to a ‘selenium insurance policy’ whereby the investment of building body selenium reserves will eventually protect against or prevent metabolic setbacks from occurring when a stress event does occur, which is especially important given stress events cannot be predicted.
Surai, P.F. (2006). Selenium in Nutrition and Health. Nottingham University Press, Nottingham.
Thomson, C. D. Selenium and iodine intakes and status in New Zealand and Australia. British Journal of Nutrition (2004) 91: 661-672