Selenium is important for poultry because it acts as an anti-oxidant. In biological systems, when oxidation of tissues for instance takes place, it creates harmful effects for the animal or organism. This oxidation process breaks down the tissues and the waste products of this process are toxic.

Selenium (and for instance vitamine E) are easily oxidated, which protects the organism because the selenium is oxidated instead of the tissues.
Selenium is available in soils and taken up by plants, which forms an organic source of selenium for the animals. Besides that, selenium can be given in an inorganic form as well. Research has shown that this inorganic form is not as effective as the organic form, and that not all soils have sufficient selenium available.

Recently, methods have been developed to produce organic selenium on a commercial scale. This is done by having yeasts produce methionine in a selenium-enriched environment. In this process, selenium is built-in in the methionine (instead of sulfur) and in this way, made available for the birds.

Research has shown that this form of selenium is better available for the birds than inorganic selenium. For instance, this can also have a positive effect on semen quality. With artificial insemination, it has been reported that using selenium-enriched mehionine resulted in an increase in hatchability. Also positive effects on egg production have been reported.

Although there is no research available yet, perhaps a positive effect on embryo viability after prolonged storage can be expected as well. This is when the embryo during storage, would be more protected against the negative effects of oxidation. However, this hypothesis is not proven, or even under research yet.