Gelsemium elegans extract powder alleviates high stocking density-related adverse effects in broilers via immune-intestinal microbiota synergistic mechanisms.

This study aimed to investigate the effects of different doses of Gelsemium elegans extract powder (GEE) on broilers under high stocking density (HSD). A total of 78 one-day-old male yellow-feathered broilers were randomly assigned to 5 treatment groups: normal stocking density (NSD), HSD, HSD + 0.06% GEE, HSD + 0.12% GEE, and HSD + 0.6% GEE. The results showed that HSD impaired broiler growth and physiological functions. Dietary supplementation with 0.06% GEE (200 mg/kg diet Gelsemium elegans extract) significantly improved growth performance (marked increases in body weight, average daily feed intake, and average daily gain), reversed immune organ inhibition (evidenced by significantly increased weight and index of the spleen and bursa of Fabricius), reduced serum corticosterone levels, repaired intestinal structural damage, and corrected intestinal flora imbalance (with a decreased Firmicutes/Bacteroidetes ratio) (P < 0.05). However, medium and high doses of GEE (0.12% and 0.6%, 400 and 2000 mg/kg diet Gelsemium elegans extract) inhibited broiler growth by inducing abnormal expression of myostatin. Therefore, 0.06% GEE (200 mg/kg diet Gelsemium elegans extract) was identified as an effective and safe dose under the current experimental conditions. In conclusion, dietary supplementation with 0.06% GEE (200 mg/kg diet Gelsemium elegans extract) can effectively improve broiler growth performance and physiological functions under HSD, and its mechanism involves reducing serum corticosterone levels, enhancing immune function, repairing intestinal morphological damage, and correcting intestinal flora imbalance.