## 3 Results
### LD\({}_{50}\) Bioassay of Se-enriched DB-Yeast  
To understand the toxicity of Se-enriched DB-yeast as a fodder additive, Na\({}_{2}\)SeO\({}_{3}\) and Se-enriched DB-yeast were evaluated by the Horn method using mouse as the biological indicator. As shown in Table 3, the LD\({}_{50}\) of Na\({}_{2}\)SeO\({}_{3}\) was 20.0 mg/kg BW (5.08 mg/kg of Se content, 13.7-21.9 mg/kg BW at 95% confidence bounds), which was identified as a highly toxic level. Surprisingly, after fermentation accumulation by DB-yeast, the LD\({}_{50}\) of Se-enriched DB-yeast was 9260.0 mg/kg BW (18.97 mg/kg of Se content, 6360.0-13,500.0 mg/kg BW at 95% confidence bounds), which was identified as a non-toxic level. Fodder Bioassays of Na\({}_{2}\)SeO\({}_{3}\) and Se-enriched DB-yeast as the Fodder Additive for Mouse and GIFT  
For mouse fodder bioassays, the effects of different Se sources, including Na\({}_{2}\)SeO\({}_{3}\) (0.2 mg/kg Se) and Se-enriched DB-yeast (0.2 mg/kg Se), on mouse growth after 21 days of feeding are shown in Table 4. After 21 days of feeding, the weights of all treated mice increased (the weight gain rates of feeding folders with no Se additive, Na\({}_{2}\)SeO\({}_{3}\) additive, and Se-enriched DB-yeast additive were \(35.42\pm 1.81\%\), \(40.12\pm 2.07\%\), and \(40.62\pm 1.78\%\), respectively). The weight gain rates of the Na\({}_{2}\)SeO\({}_{3}\) additive group and Se-enriched DB-yeast additive group were obviously (approximately 5.0%) higher than that of the no Se-additive group; however, there was no difference between them. Interestingly, the serum GSH-Px of both the Na\({}_{2}\)SeO\({}_{3}\) additive group (\(280.72\pm 8.82\) U, increased approximately 23.1%) and the Se-enriched DB-yeast additive group (\(293.05\pm 9.63\) U, increased approximately 28.5%) was significantly higher than that of the no Se-additive group (\(228.11\pm 9.27\) U). Surprisingly, compared with the Na\({}_{2}\)SeO\({}_{3}\) additive group, the serum GSH-Px of the Se-enriched DB-yeast additive group was only slightly increased (approximately 4.4%). Not surprisingly, compared with the no Se-additive control, both the Na\({}_{2}\)SeO\({}_{3}\) and Se-enriched DB-yeast could significantly promote Se sedimentation for all mouse organs including liver, serum, intestine, spleen, and muscle. Remarkably, the Se sedimentation contents of all mouse organs from the Se-enriched DB-yeast additive group were significantly higher than those of the Na\({}_{2}\)SeO\({}_{3}\) additive group. The Se sedimentation content of the Na\({}_{2}\)SeO\({}_{3}\) additive group was approximately 2.9 times (1.46 \(\pm\) 0.21 mg/kg), 2.6 times (2.53 \(\pm\) 0.18 mg/kg), 2.0 times (0.79 \(\pm\) 0.06 mg/kg), 2.5 times (5.16 \(\pm\) 0.52 mg/kg), and 3.1 times (0.34 \(\pm\) 0.02 mg/kg) higher than the no Se-additive group for liver, serum, intestine, spleen, and muscle, respectively. In addition, the Se sedimentation content of the Se-enriched DB-yeast additive group was approximately 3.8 times (5.55 \(\pm\) 0.56 mg/kg), 1.4 times (3.47 \(\pm\) 0.26 mg/kg), 4.7 times (3.74 \(\pm\) 0.34 mg/kg), 2.0 times (10.47 \(\pm\) 0.79 mg/kg), and 1.4 times (0.46 \(\pm\) 0.05 mg/kg) higher than the Na\({}_{2}\)SeO\({}_{3}\) additive group for liver, serum, intestine, spleen, and muscle, respectively. For GIFT fodder bioassays, the effects of different Se sources, including Na\({}_{2}\)SeO\({}_{3}\) (0.6 mg/kg Se) and Se-enriched DB-yeast (0.6 mg/kg Se), on GIFT growth after 60 days feeding are shown in Table 5. After 60 days of feeding, the average body weight in each experimental group increased and no deaths occurred. The weights of the feeding folders with no Se additive, Na\({}_{2}\)SeO\({}_{3}\) additive, and Se-enriched DB-yeast additive increased by 202.46 \(\pm\) 6.02%, 217.37 \(\pm\) 2.23%, and 219.40 \(\pm\) 2.84%, respectively.