Objective  The study aimed to explore the effects of Enterococcus faecium extracellular vesicles (Efm-EV) on growth performance, immunity, intestinal morphology and fecal microbiota in mice, providing theoretical basis for the application of E. faecium as a microbial feed additive in animal production.

Method  A total of 20 male C57BL/6 mice were randomly divided into control group and experimental group with 10 replicates per group and 1 mouse per replicate. The experiment lasted for 5 days. Mice in the experimental group were given 500 μg Efm-EV suspension every other day by intragastric administration, with 150 μL for each mouse, and mice in the control group were given the same volume of PBS. Daily feed intake, and body weight at the beginning and end of the experiment of each mouse were recorded, average daily gain (ADG), average daily feed intake (ADFI) and feed/gain (F/G) of mice were calculated accordingly.

Result  Compared with the PBS treatment group, no significant change was observed in the final body weight (FBW), ADG, ADFI and F/G of mice in the Efm-EV treatment group. The serum immunoglobulin A (IgA) and immunoglobulin G (IgG) levels in the Efm-EV group were significantly decreased compared with those in PBS treatment group (P < 0.05), while the serum interleukin-10 (IL-10) level was significantly increased (P < 0.05), and there was no significant difference in serum tumor necrosis factor-α (TNF-α) level. Compared with the PBS treatment, Efm-EV treatment significantly increased duodenal villus height/crypt depth ratio (VH/CD) (P < 0.05). There were no significant changes in villus height (VH), crypt depth (CD) of duodenum, and VH, CD and VH/CD of jejunum and ileum. Efm-EV intragastric administration increased the number of Firmicutes and decreased the number of Bacteroidetes at the phylum level, increased the abundance of Lachnospiraceae and decreased the abundance of Muribaculaceae at the family level, significantly increased the abundance of Ruminococcaceae UCG009 at the genus level (P < 0.05).

Conclusion  Intragastric administration of Efm-EV can improve the anti-inflammatory level, the duodenal morphology and the relative abundance of Ruminococcaceae UCG009 in mice.