**5. Conclusions**

The role of selenium in animals is reviewed and discussed. Selenium deficiency can lead to many diseases in animals, as can selenium overdose. The bioavailability of Se depends on the chemical form of supplementation and animal species exposed to a Seenriched diet and requires further investigation. Nanotechnology offers novel "intelligent" solutions in animal nutrition, health protection, and animal production systems. There are many applications of NPs in animal production, but the results of various studies that have evaluated the effects of dietary SeNP inclusion are ambiguous. The biological synthesis of SeNPs using bacteria, plants, and algae shows a grea<sup>t</sup> opportunity for further application in various fields as well in animal nutrition and production. Thus, further detailed studies in this field are required to achieve more optimized green methods of NP synthesis and application in animal diets.

**Author Contributions:** Conceptualization, S.M. and S.S.; writing—original draft preparation, S.M., P.H., and S.S.; writing—review and editing, P.H., S.S., J.S., P.S. and S.M.; supervision, P.H.; project administration, J.S. and P.H.; funding acquisition, P.H. and S.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Technological Agency of the Czech Republic (TACR) from the project TJ04000198.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data presented in this study are available upon request from the corresponding author.

**Acknowledgments:** The review article was supported by funding from the Technological Agency of the Czech Republic (TACR) from the project TJ04000198. The authors would also like thank the editor for their useful comments and suggestions, as well as two reviewers.

**Conflicts of Interest:** The authors declare no conflict of interest regarding of publication of this article.
