Influence of Astragalus extract on Gut Microbiome Regulation and Ammonia Emission Mitigation in Laying Hens

Astragalus extract plays a dual role in gut microbiome regulation and ammonia (NH₃) emission mitigation in laying hens. This study explored its effects through feeding experiments, with a focus on gut microbial metabolic pathways and NH₃ reduction mechanisms. To achieve this, both in vitro fermentation experiments and in vivo feeding trials were conducted. In the in vitro study, cecal contents from laying hens were incubated with different concentrations of AE and Yucca extract (YE) to evaluate NH₃ production, while in the feeding trial, 58-week-old Lohmann Pink laying hens were allocated into three groups (control, 0.1% YE, and 0.1% AE) and housed in controlled-environment respiration chambers for 21 days. Measurements included NH₃ emissions, serum biochemical indices, immune parameters, gut physicochemical properties, and 16S rRNA-based microbiota analysis. Results showed that Astragalus extract reduced NH₃ emissions by 29.3%, achieved by lowering urease and uricase activities and promoting the conversion of ammonium nitrogen to nitrate nitrogen. Additionally, it significantly enhanced gut immune function by increasing intestinal immunoglobulin levels. Microbial community analysis revealed an increased relative abundance of Bacteroides, Muribaculaceae, and Faecalibacterium, which are negatively correlated with NH₃ emissions. These microbial shifts improved ammonium nitrogen utilization via the upregulation of CTP synthase and GMP synthase activities, contributing to higher NH₃ reduction efficiency. This study highlights Astragalus extract as a cost-effective and sustainable strategy to regulate gut microbiota, optimize nitrogen metabolism, and mitigate NH₃ emissions in laying hens.