Lactobacillus salivarius D5 improves growth performance and immune function in broilers by reducing Escherichia coli abundance and regulating the gut microbiota

Abnormal proliferation of Escherichia coli ( E. coli ) in the intestinal tract of broilers can lead to diseases, resulting in severe economic losses. Probiotics have attracted increasing attention for their beneficial effects, such as antagonizing pathogenic bacteria and improving gut health. This study aimed to screen probiotic strains capable of inhibiting E. coil and investigate their effects on broiler growth performance and overall health. Based on evaluations of antibacterial activity, stress tolerance, and adhesion capacity in vitro , Lactobacillus salivarius D5 (L. salivarius D5), Lactobacillus agilis IM7 (L. IM7), and Lactobacillus johnsonii DM11 (L. johnsonii DM11) were selected for feeding trials in broilers. At the conclusion of the 42-day feeding period, L. salivarius D5 significantly increased the average daily gain ( ADG ) of broilers (P < 0.05) and exhibited a trend toward reducing the feed conversion rate ( FCR ) (P = 0.053). Further analysis revealed that D5 significantly increased the spleen index and serum IgM levels, while markedly promoting villus development in the jejunum and ileum, as well as the expression of intestinal IL-10 (P < 0.05). Additionally, D5 also reshaped the cecal microbiota structure, increasing the Firmicutes/Bacteroidetes ratio and the abundance of beneficial genera (such as Alistipes and Lactobacillus ), while concurrently reducing the abundance of potential pathogenic bacteria (such as Petroclostridium ) in the intestine. Results from 16S rRNA sequencing and absolute quantification consistently demonstrated that D5 effectively inhibited E. coli proliferation in the intestine, particularly in the duodenum (P < 0.05). In conclusion, L. salivarius D5 enhanced broiler growth performance by suppressing E. coli, improving microbial balance, strengthening immune function, and promoting intestinal development. These findings suggest that L. salivarius D5 holds potential as a feed additive in broiler production.