F experimental conditions, as demonstrated on many occasions, dietary supplementation with both the inorganic and organic selenium resulted in similar animal and bird performance. However, tissue accumulation was significantly greater when the organic forms of Se were fed, which is in accord with the literature. Interestingly, the yeast enriched with SeHLan generated significantly higher Se concentrations in muscle tissue than the selenomethionine enriched product. The implication of this finding in both pigs and broilers may imply a greater efficacy of SeHLan in stressful commercial environments.
Remarks
Selenium’s nutritional essentiality was discovered in the 1950s. Figure 2. Proposed metabolic pathways for SeHLan and It is now clear that the importance of having SeMet in animal cells (Source: Tsuji et al. 2010) adequate amounts of Se in the diet is primarily due to the fact that this micronutrient is required for the biosynthesis of selenocysteine as a part of functional selenoproteins. capacity to accumulate Se. The major product in selenized yeast Although animals, and presumably humans, are able to is selenomethionine. efficiently utilise nutritionally adequate levels of Se in both Selenomethionine was found to be four times more effective organic and inorganic forms for selenoprotein synthesis, it is clear than selenite in preventing the characteristic pancreatic that the bioavailability of Se varies, depending on the source and degeneration caused by selenium deficiency in chicks. chemical form of the Se supplement. Selenium yeast (selenomethionine) was found to be much more Tissue enrichment with Se is greater when organic forms of the effective than inorganic Se in increasing the Se concentration micronutrient are fed. of cow’s milk. This is in accord with many animal studies and Organic selenium, in the form of yeast enriched with human clinical trials that have demonstrated the superior efficacy of L-selenomethionine, in increasing Se muscle content compared selenomethionine, is widely used in animal nutrition. Recently, yeast enriched with SeHLan became commercially available to inorganic Se. and initial research suggests that it may be more efficacious than Selenohomoalanthionine (SeHLan; 2 hydroxy-4selenomethionine for tissue accumulation of Se. methylselenobutanoic acid) was recently identified in Japanese This has obvious implications for the production of Se enriched pungent radish and has generated much interest as it was less animal products but may also be important in commercial toxic in human cell culture than selenomethionine. As shown production units. Greater tissue reserves of Se may enhance an in Figure 2, differences in metabolism between SeHLan and animals’ resilience to stress and disease challenge. selenomethionine may, in-part, explain the apparent difference in toxicity. Selenomethionie mimics methionine by sharing the same Further reading Bellinger FP, Raman AV, Reeves MA, Berry MJ. 2009. Regulation metabolic pathways and can replace methionine in peptide and function of selenoproteins in human disease. Biochemical synthesis, as noted above, and thus disrupt protein synthesis. Journal, 422:11-22. As shown in Figure 2, the proposed metabolic pathway for SeHLan appears to be much less complex; SeHLan is only utilised in the trans-selenation pathway for selenoprotein synthesis and therefore is not expected to interfere with the methionine metabolic pathways. The tissue distribution of these two selenoamino acids may also contribute to differences in toxicity. Both are distributed throughout the body with higher liver and pancreas accumulation of selenomethionine in contrast to SeHLan which preferentially accumulates in the liver and kidneys. At higher doses, selenomethionine has been shown to induce pancreas damage whereas SeHLan is excreted by the kidneys without inducing pancreatic damage. Selenomethionine enriched yeast has been available commercially for many years. Recently, a yeast product enriched with SeHLan has become available and a number of efficacy studies with growing pigs and broiler chickens have been conducted in Australia with these selenoamino acid sources. In the studies both selenomethionine (Sel Plex) and SeHLan (AB Tor-Sel) were compared to sodium selenite. In the clean 42 | Milling and Grain
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