Glycyrrhiza uralensis-Atractylodes macrocephala combination supplementation enhances broiler growth performance, immunity, and intestinal health, potentially mediated through gut microbiota and metabolites.

The poultry industry requires effective antibiotic alternatives to enhance growth and maintain health. This study investigated the effects of the Glycyrrhiza uralensis-Atractylodes macrocephala combination (GA) on growth, meat quality, and health in broilers. One-day-old male Lingnan yellow broilers were randomly assigned to a control group (fed a basal diet) and two treatment groups that received diets supplemented with 0.1% (LGA) and 0.3% (HGA) GA, respectively. The experiment lasted for 84 days. The results showed that HGA significantly enhanced average daily gain (ADG) in broilers aged 29-56, 57-84, and 1-84 days, accompanied by a decreased feed-to-gain ratio (F/G). HGA increased carcass performance by increasing leg muscle rate and decreasing abdominal fat rate at day 84, and improved meat quality by reducing L* and b* values and shear force, and increasing a* value in breast muscle. HGA elevated the thymus and bursa of Fabricius indices and serum immunoglobulin A (IgA), immunoglobulin M (IgM), and interleukin-10 (IL-10) levels, while decreasing interleukin-2 (IL-2) and tumor necrosis factor-α (TNF-α) levels. Moreover, HGA increased jejunal villus height (VH) and villus height/crypt depth (VH/CD), and secretory immunoglobulin A (sIgA) content and mRNA expression of ZO-1 and CLDN1. It also modulated the cecal microbiota composition and altered microbial interactions in an age-dependent way. Specifically, HGA increased the abundance of short-chain fatty acids-producing or anti-inflammatory-associated bacteria, such as Rikenellaceae_RC9_gut_group, Negativibacillus, Enterococcus, Butyricicoccus, and Muribaculaceae, while decreasing the abundance of pro-inflammatory-associated bacteria, such as Parasutterella, Desulfovibrio, and Campylobacter. Metabolomic analysis revealed that HGA altered cecal metabolic profiles by upregulating key metabolites, including 3α, 7α, 12α-trihydroxy-5β-cholestanoate, enoxolone, and butyric acid. In conclusion, HGA enhances production performance, immune function, and intestinal barrier integrity in broilers, where shifts in gut microbiota and metabolites may contribute to these beneficial outcomes. These findings provide a solid scientific basis for the design and utilization of herbal feed additives.