Supplementation of feed with Se is now a common practice in the poultry industry. In the
European Union, the limit for use of Se additive is 0.5 mg Se milligram per kilogram of the
complete feeding stuff, while the maximum permitted Se inclusion level in the USA is
0.3 ppm [1, 2]. From approving of selenium as a feed supplement in 1970 in Europe and
1974 in the USA, sodium selenite (SS) has become the traditional source of Se for
supplementation of poultry and livestock nutrition. Organic form of Se, selenium-enriched
yeast (SY), was approved in 2000 in USA, while in Europe not before. Selenomethionine
(SM), a Se analog of methionine, is the predominant form of selenium in SY [3]. Selenium
concentration in eggs reflects its content and form in feed. Many researchers have shown
that the increasing concentration, both inorganic and organic Se forms in the feed, results in
the whole-egg Se content increase and that SY and SM are more effective than SS [4–8].
Generally, cited researches observed the effects of supplementation in a relatively short
period and those do not give sufficient data about the effects of supplementation with Se
over permitted but not toxic level. Also, the researches obtained different concentration of
selenium in eggs for the same dietary Se source and inclusion level. Therefore, the main
objective of this study was to compare the effects of various levels of SY and SS, over
permitted, on Se deposition in the eggs and hen’s productivity, over a 16-week period.