## 4 Discussion  
At a high concentration, Se is toxic and affects the central nervous system; however, at a low concentration, Se is an essential microelement for humans since its prominent effects in disease and cancer prevention are well documented [2; 5; 8]. Se exists in nature in inorganic and organic forms. Both types of Se can prevent and treat various diseases caused by Se deficiency. However, organic \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Test Items**} & **No Se-Additive** & **Na\({}_{2}\)SeO\({}_{3}\) Additive** & **Se-Enriched DB-Yeast** \\  & **Control** & **0.2 mg/kg Se** & **Additive 0.2 mg/kg Se** \\ \hline Weight gain rate 1 ** & 40.62 \(\pm\) 1.78 2 \\ GSH-Px & 228.11 \(\pm\) 9.27 & 280.72 \(\pm\) 8.82 3  \\  & Liver & 0.50 \(\pm\) 0.07 & 1.46 \(\pm\) 0.21 2 3  \\ Se sedimentation & Serum & 0.98 \(\pm\) 0.07 & 2.53 \(\pm\) 0.18 2 3  \\  & Intestine & 0.39 \(\pm\) 0.05 & 0.79 \(\pm\) 0.06 4  \\  & Spleen & 2.04 \(\pm\) 0.16 & 5.16 \(\pm\) 0.52 4  & 10.47 \(\pm\) 0.79 5 \\ Muscle & 0.11 \(\pm\) 0.03 & 0.34 \(\pm\) 0.02 4  \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Effects of the Se source on mouse growth after 21 days of feeding. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Test Items**} & **No Se-Additive** & **Na\({}_{2}\)SeO\({}_{3}\) Additive** & **Se-Enriched DB-Yeast** \\  & **Control** & **0.6 mg/kg Se** & **Additive 0.6 mg/kg Se** \\ \hline Weight gain rate 1  \\ Serum & 29.3 \(\pm\) 0.17 & 3.41 \(\pm\) 0.20 4  \\ Se sedimentation & Intestine & 3.22 \(\pm\) 0.24 & 5.42 \(\pm\) 0.48 4  \\ content 2 [FOOTNOTE:2]Footnote 2: Statistically significant for Na\({}_{2}\)SeO\({}_{3}\)-containing folder compared with control (\(p\)-value \(<0.05\)); 2 statistically significant for Se-enriched DB-yeast-containing folder compared with control (\(p\)-value \(<0.05\))Se is less toxic and has a higher absorption rate than inorganic Se [14; 15]. In this study, inorganic Se (Na\({}_{2}\)SeO\({}_{3}\)) was bio-transformed into organic Se (Se-enriched DB-yeast) through fermentation accumulation by re-using DB-yeast obtained from the beer industry for Se-enriched fodder application. The bioavailability and non-toxic characteristics of Se-enriched DB-yeast indicated that it has the potential to be used as a safe and effective Se-enriched fodder additive. DB-yeast was chosen as the Se accumulation carrier to avoid the potential risk of pollution and to limit wasting of resources. However, DB-yeast is not a professional Se accumulation carrier; therefore, a single-factor experiment and an \(L_{9}(3^{4})\)-orthogonal test for optimization of fermentation conditions were employed to improve its Se accumulation capacity before incorporating it as a fodder additive. To easily obtain the fermentation medium, beer industry fermentation medium was directly used for the initial fermentation medium for the DB-yeast. Interestingly, temperature, pH, and Brix of the initial fermentation condition did not significantly affect the Se accumulation capacity of the DB-yeast, indicating that it is easy to control the fermentation conditions by controlling the concentration of added Se, the time of Se addition, and inoculation volume. Furthermore, the concentration and timing of the added Se can significantly affect the Se accumulation capacity of _S. cerevisiae_. [PERSON] et al. [13] reported that, after fermentation condition optimization, using a culture medium supplemented with 15.0 \(\mu\)g/mL Na\({}_{2}\)SeO\({}_{3}\) added at 9 h after inoculation, which is during the logarithmic growth phase, the total Se content and the maximum biomass in a _S. cerevisiae_ strain could reach 5.9 mg/L and 9.23 g/L, respectively. [PERSON] et al. [29] reported one _S. cerevisiae_ isolate with high levels of Se accumulation capacity (reaching 1.4 mg/g) incubated in an optimized Se accumulation medium (containing 25.2 \(\mu\)g/mL Na\({}_{2}\)SeO\({}_{3}\)) after directed evolution by glycerol- and selenium-containing medium selection.