Dietary rosmarinic acid alleviates PM2.5-triggered pulmonary injury in broilers: insights into inflammatory signaling, pulmonary microbiota and metabolic modulation.

Fine particulate matter (PM2.5) has become a severe environmental hazard in intensive poultry farming, which commonly triggers respiratory impairment and further deteriorates the growth performance and health status of broilers. Developing feasible dietary additives to relieve PM2.5-caused toxic damage is urgently required for the modern poultry industry. Rosmarinic acid (RA) is a naturally occurring polyphenolic compound with validated anti-inflammatory and antioxidative capacities; nevertheless, whether dietary RA can ameliorate pulmonary damage induced by PM2.5 pollution in broilers remains poorly understood. The present study aimed to explore the protective potential and molecular mechanisms of RA against PM2.5-mediated lung injury in broiler models. A total of 144 male Arbor Acres (AA) broilers at 21 days of age were randomly assigned to three groups: control group (CON), PM2.5 exposure group (PM), and PM2.5 exposure supplemented with 200 mg/kg RA group (RA). The experimental feeding period lasted for 21 days. The results showed that RA supplementation effectively mitigated pulmonary inflammatory lesions caused by PM2.5 exposure, which was accompanied by improved lung histological morphology and decreased secretion of inflammatory cytokines (IL-6, IL-10, TNF-α, and IFN-γ). Molecular detection confirmed that RA intervention effectively inhibited the overactivation of the TLR4/MyD88/NF-κB inflammatory cascade. Moreover, dietary RA reshaped the pulmonary microbial community structure by elevating bacterial richness and evenness. The relative abundances of beneficial bacterial genera (Turicibacter, Hydrogenophilus, and Actinoplanes) were enriched, whereas taxa including Ammoniibacillus, Thermobacillus, and Hyphomicrobium were depleted. Untargeted metabolomic analysis screened a total of 66 differential metabolites, which were mainly annotated to tryptophan metabolism, tricarboxylic acid (TCA) cycle, arginine biosynthesis, and glycerophospholipid metabolism pathways. Collectively, these results demonstrate that 200 mg/kg dietary RA protects broilers from PM2.5-triggered pulmonary injury via inhibiting the TLR4/MyD88/NF-κB inflammatory pathway, optimizing lung microbial composition, and regulating metabolic patterns. This research offers empirical evidence to support the application of RA as a promising feed additive for maintaining respiratory health of broilers exposed to PM2.5 contamination.