A succession of pulmonary microbiota in broilers during the growth cycle.

Respiratory health problems in poultry production are frequent and knotty and thus attract the attention of farmers and researchers. The breakthrough of gene sequencing technology has revealed that healthy lungs harbor rich microbiota, whose succession and homeostasis are closely related to lung health status, suggesting a new idea to explore the mechanism of lung injury in broilers with pulmonary microbiota as the entry point. This study aimed to investigate the succession of pulmonary microbiota in healthy broilers during the growth cycle. Fixed and molecular samples were collected from the lungs of healthy broilers at 1, 3, 14, 21, 28, and 42 d of age. Lung tissue morphology was observed by hematoxylin and eosin staining, and the changes in the composition and diversity of pulmonary microbiota were analyzed using 16S rRNA gene sequencing. The results showed that lung index peaked at 3 d, then decreased with age. No significant change was observed in the α diversity of pulmonary microbiota, while the β diversity changed regularly with age during the broilers' growth cycle. The relative abundance of dominant bacteria of Firmicutes and their subordinate Lactobacillus increased with age, while the abundance of Proteobacteria decreased with age. The correlation analysis between the abundance of differential bacteria and predicted function showed that dominant bacteria of Firmicutes, Proteobacteria and Lactobacillus were significantly correlated with most functional abundance, indicating that they may involve in lung functional development and physiological activities of broilers. Collectively, these findings suggest that the lung has been colonized with abundant microbiota in broilers when they were just hatched, and their composition changed regularly with day age. The dominant bacteria, Firmicutes, Proteobacteria, and Lactobacillus, play crucial roles in lung function development and physiological activities. It paves the way for further research on the mechanism of pulmonary microbiota-mediated lung injury in broilers.