Decoding the dynamics of calves' respiratory and gut microbiota: exploring stability, resistance, and individual patterns.

We investigated the early-life interplay between microbiota, host, and environment by longitudinally monitoring nasal and gut microbiota in 30 veal calves over their first five months of life. Microbial composition and stability were highly compartmentalized. Fecal communities showed increasing biomass, diversity, and homogeneity with age. Conversely, nasal microbiota remained less diverse and highly variable between individuals, likely influenced by mucociliary clearance and transient colonization. Environmental factors, diet, and clinical indicators were associated with both microbial communities, alongside distinct cytokine profiles. As calves matured, microbiota dynamics and composition covaried across body sites, reflecting systemic immune development and environmental adaptations. This study provides a comprehensive, multi-layered characterization of microbial dynamics, identifying the first month of life as a critical window for interventions targeting the fecal microbiota. The nasal microbiota, by contrast, remains flexible and amenable to modulation throughout the production cycle.