In ovo dose-response characterization of Lactiplantibacillus plantarum HY7715 reveals coordinated physiological and microbiome responses in vivo (Gallus gallus).

In ovo probiotic delivery provides a controlled in vivo platform for studying early host-microbiome interactions, yet dose-dependent multi-system responses remain insufficiently characterized. This study evaluated a commercially developed strain, Lactiplantibacillus plantarum HY7715 (Lpb. plantarum HY7715 in text, LPHY in figures and sequence ID codes), administered in ovo across a graded dose range (3.2 × 105 to 4.1 × 107 CFU/mL) in Gallus gallus, to assess intestinal development, skeletal muscle gene expression, and cecal microbiome structure and inferred function. In ovo administration was well tolerated, with no effects on hatchability or growth parameters. Lpb. plantarum HY7715 induced dose-dependent intestinal remodeling, including increased villus height, crypt depth, goblet cell abundance, and villus surface area, together with elevated duodenal MUC2 expression, indicating enhanced mucosal barrier maturation. Effects were tissue specific, with limited colonic transcriptional responses, suggesting spatial heterogeneity in embryonic intestinal responsiveness. At the systemic level, Lpb. plantarum HY7715 modulated skeletal muscle transcription in a dose-dependent manner, including upregulation of myogenin and downregulation of mTOR signaling and myosin heavy chain isoforms, indicating altered myogenic differentiation trajectories. Cecal microbiome analysis confirmed successful Lactiplantibacillus colonization and revealed dose-associated shifts in community structure and inferred metabolic function, including enrichment of myo-inositol and citrulline biosynthetic pathways at higher doses. Collectively, these findings demonstrate that the in ovo Gallus gallus model enables robust in vivo dose-response characterization of probiotic effects across multiple biological systems, using the commercially developed strain Lpb. plantarum HY7715 as a representative probiotic candidate.