In this study, we evaluated the phylogenetic diversity of the cecal microbiota of 3-week-old ducklings fed three diets differing in metabolizable energy. The contents of the ceca were collected from ducklings of different groups. The ceca bacterial DNA was isolated and the V3 to V4 regions of 16S rRNA genes were amplified. The amplicons were subjected to high-throughput sequencing to analyze the bacterial diversity of different groups. The predominant bacterial phyla were Bacteroidetes (~65.67%), Firmicutes (~17.46%), and Proteobacteria (~10.73%). The abundance of Bacteroidetes increased and that of Firmicutes decreased with increasing dietary energy level. The diversity decreased (Simpson diversity index and Shannon diversity index) with the increase in dietary energy level, but the richness remained constant. Notably, Brachyspira bacteria were detected with a very high relative abundance (4.91%) in ceca of ducks fed a diet with 11.30 MJ/kg metabolizable energy, suggesting that low energy content may affect their colonization in cecum.

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