This study was conducted to investigate how chito-oligosaccharides (COSs) affect the growth performance and immune stress response and to further explain their mechanisms. A total of 32 boars that were 28 days old and three-way weaned were randomly allotted to four equal groups [CON (basal diet) group, enterotoxigenic Escherichia coli (ETEC) group, COS group, and COS*ETEC group]. The results showed that COS partially reversed the negative changes in the average daily gain and average daily feed intake caused by the ETEC challenge and thereby alleviated the increase in the feed conversion ratio. Dietary COS increased the villus length as compared with the CON group and improved the ileal morphological structure. Additionally, it increased the bacterial diversity and Bacteroidetes abundance and lowered the Firmicutes abundance and Firmicutes-to-Bacteroidetes ratio at the phylum level. COS treatment lowered the abundance of Lactobacillus, Streptococcus, and Anarovovrio in the intestines of piglets, while it increased Muribaculaceae_unclassified and Prevotella at the genus level. COS had a significant inhibitory effect on the increase in the relative expression abundance of STAT3 mRNA caused by ETEC. The IL-10 and FOXP3 mRNAs were found to be significantly lower in the COS, ETEC, and COS*ETEC groups as compared to the CON group. These results demonstrate that COS could be beneficial for improving the growth performance and attenuating ETEC-challenged intestinal inflammation via regulating microbiota and Th17/Treg balance-related immune signaling pathways.

In order to study the regulation of Fenugreek seed extract (FSE) on the immunity of broilers, and explore the appropriate amount of FSE in broilers' production, 1-day-old yellow feather broilers with a total of 420 birds were randomly allocated into seven treatments. Each treatment had six replicates, with 10 birds per replicate. The two control groups were the basic fodder group fed with basal diet and the bacitracin zinc group added 30 mg/kg bacitracin zinc to the basal diet. Experimental groups included five levels of FSE (50, 100, 200, 400, and 800 mg/kg FSE to the basal diet, respectively). The pre-test period was 7 days and the formal test lasted for 56 days. The results showed that the average daily gain (ADG) of 50 and 800 mg/kg FSE groups was significantly increased (P < 0.01), and the feed to gain ratio (F/G) of FSE groups was significantly decreased (P < 0.01) compared with the basic fodder and the bacitracin zinc groups. Compared with the basic fodder group, the serum total cholesterol (TC) content in the FSE groups was significantly decreased (P < 0.05), the serum low density lipoprotein cholesterol (LDL-C) content of 50, 100, and 800 mg/kg FSE groups was significantly lower than that of the basic fodder group (P < 0.05). Compared with the basic fodder and bacitracin zinc groups, the serum immunoglobulins (IgG, IgM, IgA) content of 100 and 200 mg/kg FSE groups were significantly increased (P < 0.05). Compared with the bacitracin zinc group, the serum interleukins (IL-1, IL-10) content of 400 mg/kg FSE group were significantly increased (P ≤ 0.05), and the serum interferon-γ (IFN-γ) content of 100 and 200 mg/kg FSE groups was significantly increased (P < 0.05). Compared with the basic fodder group, the lower doses (0–400 mg/kg) of FSE had no significant effect on the mRNA expression of toll-like receptors 4/ myeloid differentiation factor 88/ nuclear factor-κB (TLR4/MyD88/NF-κB) signaling pathways (P > 0.05). The 800 mg/kg FSE treatment group significantly increased the expression levels of nuclear factor-κB (NF-κB) mRNA in the spleen of broilers (P < 0.05). The zinc bacitracin group significantly increased the expression levels of myeloid differentiation factor 88 (MyD88) and nuclear factor-κB (NF-κB) mRNA (P ≤ 0.05). The results showed that FSE could promote the secretion of immunoglobulins, regulate the body's cytokines, and have a positive effect on immunity in broilers. Furthermore, the recommended supplement of FSE is 100 mg/kg in the broiler diet.