## 4 Discussion  
Previous studies indicated that early intervention with fecal microbiota has beneficial effects on improving growth performance and reducing the diarrhea rate in suckling piglets [2; 7]. In this study, we performed an early intervention trial, and try to apply the method of early intervention to actual production. According to the results, early intervention with FMT can increase the growth performance and decrease the diarrhea rate, which is similar to previous studies [1; 2; 7; 10]. Furthermore, we also found that the piglets' growth performance can be further improved by early intervention using FMT combined with CB and SB on the basis of FMT, which consistent with our experimental hypothesis. To explore the reasons why FMT+C+S promoted piglets' growth performance, we determined the concentration of fecal SCFAs at different time points. Fecal SCFAs are produced by commensal bacterial fermenting indigestible dietary fibers in intestines [25; 26] and participate in innate and adaptive immune responses [27; 28]. In this study, the total SCFAs were increased during suckling period, after early intervention with FMT+C+S. The results indicated that early intervention with FMT+C+S may mainly enrich the SCFA produced bacteria. Emerging data discovered that succinate plays an important role in type 2 innate lymphoid cells (ILC2) immune response in the small intestine [29]. In addition, succinate levels were increased in GF mice reconstituted with the fecal microbiota of mice, and it is beneficial to protect against colonization by bacterial pathogens. Furthermore, administration of succinate in drinking water reduced colonization of bacterial pathogens [8]. Hence, in this study, the increased fecal SCFAs and succinate concentration may contribute to gain a healthier and more stable intestinal environment in FMT+C+S piglets. On the other hand, SCFAs could stimulate intestinal growth and improve gut barrier function in pig [30]. In animals, plasma DAO and D-LA were biomarkers for the functional status of intestinal mucosal barrier [31; 32; 33]. The mucus layer plays a vital in the modulation of the development and establishment of the gastrointestinal microbiota [34]. MUC2 is the most abundant mucin in the intestine and it has been used as a biomarker for gastrointestinal functionality [34; 35]. The higher the level of DAO,  
Figure 2: Effects of different early intervention model on the intestinal microbiota structure in piglets. All values are presented as means \(\pm\) SEM (\(n=10\)–\(12\)). \({}^{\text{a,b,c}}\) Values within a row with different superscripts differ significantly at \(p<0.05\). the more imperfect the intestinal mucosa becomes. So, our results indicated that early intervention with FMT+C+S can improve the gut barrier function. Furthermore, we quantified several representative commensal bacteria. _Escherichia coli_ is a kind of facultative anaerobic bacteria, which is planted in large quantities around 3 days after birth. Reducing the abundance of _E. coli_ in piglets at the age of 14 d and 21 d, which can effectively reduce the risk of diarrhea. _E. coli_ is one of Enterobacteriaceaeae, for which gut oxygen is a limiting resource, and the gut oxygen increases the relative abundance of Enterobacteriaceae [36], which may indicate a lower oxygen content in the gut of piglets in group FMT+C+S. _Lactobacillus_ spp. are important members of the commensal microbiota and are used as probiotics. The _Lactobacillus_ species were sensitivity toward hydrogen sulfide [37], and hydrogen sulfide was reported to be involved in intestinal inflammation [38]. It has been confirmed that early intervention could enrich the _Lactobacillus_ spp. population [7; 39]. Therefore, the increased abundance of _Lactobacillus_ spp. in our study suggests that early intervention with FMT+C+S can reduce the risk of bowel disorders. _Bifidobacterium_ genus have been shown to promote immune function [40; 41; 42].