The Development of the Gut Microbiota and Short-Chain Fatty Acids of Layer Chickens in Different Growth Periods

A long-term observation of changes of the gut microbiota and its metabolites would be beneficial to improving the production performance of chickens. Given this, 1-day-old chickens were chosen in this study, with the aim of observing the development of the gut microbiota and gut microbial function using 16S rRNA gene sequencing and metabolites short-chain fatty acids (SCFAs) from 8 to 50 weeks. The results showed that the relative abundances of Firmicutes and genus Alistipes were higher and fiber-degradation bacteria were less at 8 weeks compared with 20 and 50 weeks (P < 0.05). Consistently, gut microbial function was enriched in ATP-binding cassette transporters, the energy metabolism pathway, and amino acid metabolism pathway at 8 weeks. In contrast, the abundance of Bacteroidetes and some SCFA-producing bacteria and fiber-degradation bacteria significantly increased at 20 and 50 weeks compared with 8 weeks (P < 0.05), and the two-component system, glycoside hydrolase and carbohydrate metabolism pathway, was significantly increased with age. The concentration of SCFAs in the cecum at 20 weeks was higher than at 8 weeks (P < 0.01), because the level of fiber and the number of dominant fiber-degradation bacteria and SCFA-producing bacteria were more those at 20 weeks. Notably, although operational taxonomic units (OTUs) and the gut microbial α-diversity including Chao1 and abundance-based coverage estimator (ACE) were higher at 50 than 20 weeks (P < 0.01), the concentration of SCFAs at 50 weeks was lower than at 20 weeks (P < 0.01), suggesting that an overly high level of microbial diversity may not be beneficial to the production of SCFAs.