Fig. 3.

Organic Se in action. A range of Se-containing compounds, including selenite, selenate, SeMet, Zn-SeMet, OH-SeMet, Se-yeast, SeCys, Se-GSH, and Se-peptides, can be included into premixes. All those Se forms come to the intestine where initial hydrolysis (Se-Met will be released from Se-yeast or Zn-SeMet; OH-SeMet will be converted into SeMet) and some metabolic changes will take place. This includes excretion of Se metabolites via bile, feces, and urine. Further, selenite, selenate, SeMet and some other Se forms will be delivered to the liver for metabolization and distribution. In parallel, a fraction of SeMet will go to the free amino acid pool and be used for building Se reserves mainly in muscles. The next step of Se assimilation and metabolism includes the conversion of all major forms of Se into H₂Se, from which SeCys will be synthesized and incorporated into 26 newly synthesized selenoproteins that are integral part of the antioxidant system of the body. Under stress conditions, protein catabolism will take place, which will release some SeMet incorporated into those proteins, and this SeMet will be converted into H2Se and further into newly synthesized SeCys and 26 selenoproteins. Additional sources of Se will be responsible for the upregulation of selenoprotein genes and additional synthesis of selenoproteins, which will upregulate antioxidant defenses and will aid the body to adapt to and overcome the stress with minimal negative consequences. When only selenite is present in the diet, Se reserves in the muscles will not be built and therefore, the ability of the body to adapt to stress will be restricted.