Hyunjin Kyoung ¹ Ikcheol Shin ¹ Younghoon Kim ² Jinho Cho ³ Kyeong Il Park ¹ Yonghee Kim ¹ Jinmu Ahn ¹ Jinuk Nam ¹ Kimoon Kim ¹ Yonggu Kang ¹ Hyeun Bum Kim ^4* Minho Song ^1*

• ¹ Chungnam National University, Daejeon, Republic of Korea
• ² Seoul National University, Seoul, Republic of Korea
• ³ Chungbuk National University, Cheongju, North Chungcheong, Republic of Korea
• ⁴ Dankook University, Cheonan, Republic of Korea

This study was carried out to evaluate the effects of dietary mixed selenium [MSe; inorganic selenium (ISe) + organic selenium (OSe)] levels on the growth performance, blood parameters, and fecal microbiota of weaned pigs. In a randomized complete block design (block = initial body weight), 156 weaned pigs were allotted to three dietary treatments (4 pigs/pen; 13 replicates/treatment) for 42 days. Dietary treatments were 1) a non Se-fortified diet based on corn and soybean meal (CON), 2) CON + 0.15 ppm ISe and 0.15 ppm OSe (MSe3), and 3) CON + 0.25 ppm ISe and 0.25 ppm OSe (MSe5). Pigs fed both MSe had no effects on growth performance and diarrhea frequency of weaned pigs compared with those fed CON. However, dietary MSe3 and MSe5 had higher (p = 0.021, linear p = 0.011) serum interleukin-6 on day 7 and Se concentrations on day 42 than the CON, respectively. In addition, pigs fed different levels of MSe had quadratic (p = 0.054) and linear (p = 0.069) effects on number of white blood cells and hematocrit on day 42, respectively, compared with CON.Moreover, the MSe3 group had higher total protein concentration (p = 0.049, quadratic p = 0.026) on day 42 than the CON group, and the MSe5 group had lower blood urea nitrogen concentration (p = 0.094, linear p = 0.033). There were no differences on alpha diversity indices of fecal microbiota among dietary treatments. However, beta diversity based on Bray-Curtis was clustered differently (r 2 = 0.56, p = 0.001) among dietary treatments. Pigs fed MSe5 had increased the relative abundance of phylum Bacteroidetes [false discovery rate (FDR) adjusted p = 0.004], families Barnesiellaceae (FDR adjusted p = 0.006) and Veillonellaceae (FDR adjusted p = 0.006), genera Barnesiella (FDR adjusted p = 0.023) and Megasphaera (FDR adjusted p = 0.023), and species Barnesiella intestinihominis (FDR adjusted p = 0.016) and Megasphaera elsdenii (FDR adjusted p = 0.019) compared with those fed CON. In conclusion, dietary MSe modulated systemic health parameters and fecal microbial community of weaned pigs.