Microbiota responses to feed particle size, calcium concentration, and phytase supplementation in broiler chickens.

This research aimed to investigate the modulation of broiler-chickens gut microbiota by dietary particle size (PS), exogenous phytase, and calcium (Ca) concentration. Eight experimental diets varied in PS (fine 222 µm (PF) and coarse 309 µm (PC)), Ca concentration (4.9 and 7.2 g/kg), and exogenous phytase (0 and 1000 FTU/kg). A total of 560 Ross 308 broiler chickens were allocated to 56 metabolism units at 7 days of age and randomly assigned to each diet (7 replicates per treatment). On days 22 and 23, the birds were slaughtered, and the digesta from the gizzard, ileum, and ceca were sampled and pooled on a metabolism unit basis. DNA extraction was followed by 16S rRNA gene amplicon sequencing. Thirteen amplicon sequence variants (ASV) were present across the gizzard, ileum, and ceca, most of which were assigned to Limosilactobacillus and represented a substantial share of the total relative abundance in each section, 86 % in the gizzard, 88 % in the ileum, and 30 % in the ceca. Six of these L. reuteri ASVs were significantly enriched by coarse particle feeding, suggesting strain-specific adaptation to enhanced phosphorus availability. In the ileum, Candidatus arthromitus (p < 0.001) and Rombustia (p < 0.05) showed a significant increase in relative abundance in PC compared to PF. Phytase supplementation reduced the relative abundance of Lactobacillus and Streptococcus (p < 0.05), while higher Ca concentration decreased that of C. arthromitus (p < 0.05). In the ceca, increases in the relative abundance of Anaerostipes (p < 0.05) and Clostridia vadin BB60 were found for PC diets compared to PF (p < 0.001). The addition of phytase and Ca also significantly affected several genera, albeit the variations were less than 1 %. Dietary PS, exogenous phytase, and Ca concentration modulated the gut microbiota, specifically influencing the abundance of key microorganisms like Candidatus arthromitus, Anaerostipes, and Clostridia vadin BB60, involved in phosphorus metabolism and overall broiler chickens' health.