Exploring the Effects of Gracilaria lemaneiformis Polysaccharides on the Fecal Microbiota and Fecal Metabolites of Fattening Pigs Based on 16S rDNA and Metabolome Sequencing

Sixty Duroc × (Landrace × Yorkshire) castrated male finishing pigs were randomly divided into negative control (NC) and <i>gracilaria lemaneiformis</i> polysaccharides (GLP) groups to study the effects of GLP on the fecal microbiota and fecal metabolites of fattening pigs. The NC group was fed a basic diet, and the GLP group was fed a basic diet supplemented with 0.1% GLP. The diversity of the species and the fecal metabolites were analyzed using 16S rDNA sequencing and metabolome sequencing, respectively. The serum immune and antioxidant indices were analyzed using the ELISA assay. The abundances of hazardous bacteria such as Proteobacteria at the phylum level and <i>Shigella</i> at the genus level were extremely significantly decreased (<i>p</i> < 0.01) and those of beneficial bacteria such as Firmicutes at the phylum level (<i>p</i> < 0.01), <i>Clostridium</i> at the genus level (<i>p</i> < 0.01), and <i>Lactobacillus</i> at the genus level (<i>p</i> < 0.05) were significantly increased in the GLP group compared with the NC group. A total of 41 differentially expressed metabolites were identified. The expression of anti-inflammatory and antioxidant active substances, such as methyl cinnamate, protopanaxatriol, and isovanillic acid, was elevated in the GLP group. The ELISA assay showed increased GSH-Px activity (<i>p</i> < 0.01), T-AOC (<i>p</i> < 0.01), IgG (<i>p</i> < 0.01), IgA (<i>p</i> < 0.05), and IgM (<i>p</i> < 0.05) in the GLP group. These results indicate that dietary GLP supplementation can improve the antioxidant ability, anti-inflammatory ability, and immune level of fattening pigs by regulating fecal flora and metabolites and could be used as a functional feed additive.