Modulation of Cecal Microbiota and Inflammatory-Immune Pathways Underlies the Reduced Eliminations but Unchanged Growth in Broilers Fed a Compound Probiotic

With the global restriction on antibiotic growth promoters in poultry production, probiotics have emerged as promising alternatives. This study evaluated the effects of a compound probiotic formulation consisting of Lactobacillus salivarius, Lactobacillus acidophilus, and Lactobacillus reuteri at a ratio of 38:9:1 on growth performance and gut microbiota in Lingnan yellow-feathered broilers. A total of 700 one-day-old broilers were randomly assigned to a control group (basal diet) or a probiotic group (basal diet plus 1.45 × 109 CFU/L of the compound probiotic in drinking water, administered intermittently from 22 to 63 days of age). Growth performance, serum biochemical parameters, and intestinal morphology were measured, and 16S rRNA sequencing was performed on fecal, ileal, and cecal samples. Results showed that probiotic supplementation did not significantly affect growth performance, serum biochemical indices, or intestinal villus morphology. However, elimination rate during 43–63 days and over the entire experimental period was significantly reduced in the probiotic group. 16S rRNA sequencing revealed that the probiotic group exhibited significantly increased cecal microbial richness without alterations in community evenness, along with decreased Lactobacillus abundance in the ileum and increased Akkermansia abundance in the cecum. Functional prediction of cecal microbiota showed that 84 pathways, including inflammation- and immunity-related pathways such as the NOD-like receptor signaling pathway and multiple core functional categories, were significantly down-regulated, while only three pathways were significantly up-regulated. Collectively, although the compound probiotic failed to improve growth performance, it effectively reduced elimination rate, potentially through enrichment of beneficial Akkermansia and modulation of intestinal inflammation-related pathways.