Effect of Tryptophan Supplementation Levels on the Cecal Microbial Composition, Growth Performance, Immune Function...

Tryptophan (Trp) is a limiting amino acid in poultry nutrition. Dietary supplementation of Trp not only enhances production performance, but also supports intestinal barrier integrity, alleviates stress, and boosts immunity, in which the derivatives from gut Trp-metabolizing commensal microbes play crucial roles. However, research on how excessive Trp affects poultry growth, metabolism, and gut microbiota composition remains limited.

In this study, we investigated the effects of varying Trp levels (0.23%, 0.29%, 0.35%) on broiler production performance, immune function, and antioxidant levels through controlled feeding trials. These host responses were further correlated with cecal microbiota metagenomic sequencing data using multivariate analysis.

Compared with the basal 0.23% Trp level, a 0.35% of Trp addition significantly impaired broiler body weight gain and feed intake, and 0.29% Trp could increase thymus index and serum superoxide dismutase (SOD) level without affecting the growth performance; neither of these two levels affected the feed conversion rate. The cecal microbial metagenomic data further revealed that Trp supplementation reduced the abundance of harmful bacteria, while increasing the abundance of beneficial bacteria and Trp-metabolizing microorganisms. Correlation analysis showed that Trp supplementation was negatively correlated with body weight (BW) but positively correlated with thymus index and SOD level, with similar trends observed between the abundance of specific Trp-utilizing microorganisms and these indicators. Functional analysis revealed an increase in the abundance of KEGG orthology (KO) related to Trp metabolism from the aforementioned microbes.

An appropriate addition of Trp (0.29%) can enhance certain metabolic levels without affecting production performance, which might be achieved through relevant metabolic pathways of intestinal microorganisms.