Yang Liu ¹ Lei Cao ¹ Chenhao Yu ¹ Qiang Zhou ¹ Hua Li ¹ Ruinan Zhang ¹ Jiayong Tang ¹ Zhiming Zhang ² Zheng Luo ² Xuemei Jiang ¹ Zhengfeng Fang ¹ Yan Lin ¹ Shengyu Xu ¹ Yong Zhuo ¹ Lun Hua ¹ De Wu ¹ Bin Feng ¹ Lianqiang Che ^1*

• ¹ Institute of Animal Nutrition, Sichuan Agricultural University, Chengdu, China
• ² Kemin (China) Technologies Co., Ltd., Zhuhai, Guangdong Province, China

The objective of this study was to evaluate the effects of dietary supplementation with Bacillus subtilis PB6 on growth performance, diarrhea scores, nutrients digestibility, immune function and gut microbiota of weaned piglets fed high-protein diet. A total of 96 weaned piglets were randomly divided into 3 groups in a randomized complete block design, receiving low-protein (LP, 18.27% crude protein) diet, high-protein (HP, 20.97% crude protein) diet or high-protein diet supplemented with probiotics (HPPRO, Bacillus subtilis PB6 spores 2 × 1011 CFU/ kg) for 21 days. Each group had 8 replicates with 4 piglets per replicate. The results showed that piglets fed HPPRO diet had greater average daily gain and average daily feed intake during days 8 to 14, days 15 to 21 and overall experimental period than piglets fed LP diet (P < 0.01). In parallel, piglets fed HPPRO diet had lower F:G value during days 8 to 14 than piglets fed LP diet (P < 0.05). Piglets fed HP diet had increased diarrhea scores than piglets fed LP diet (P < 0.01), but diarrhea scores by piglets fed HPPRO diet were lower than HP piglets (P < 0.01), which had lowest nutrient digestibility. Moreover, piglets fed HPPRO diet had lower plasma concentration of haptoglobin than HP piglets (P < 0.05) and lower pig major acute-phase protein level than HP and LP piglets (P < 0.05). The down-regulation of genes (toll-like receptor-4, tumor necrosis factor-α and TNF receptor-associated factor-6) in ileal tissue associated with inflammation were observed in HPPRO piglets relative to LP and HP piglets (P < 0.05). Piglets fed HPPRO diet had increased relative abundance of genera related to proteolysis, such as g_Fusobacterium and g_Acidaminococcus, as well as the genera related to butyrate production, such as g_Anaerostipes and g_Megasphaera. Furthermore, piglets fed HPPRO diet had higher concentration of butyrate in colonic digesta than piglets fed LP diet (P < 0.05). In conclusion, piglets fed high-protein diet with 300 mg/kg Bacillus subtilis PB6 had better growth performance, associating with relatively higher nutrient digestibility and improved intestinal bacterial profile, as well as lower inflammatory response.