Multi-omics reveal beneficial effects of chrysanthemum stalks on growth performance and immune function in Hu sheep

Chrysanthemum stalks (CS), a plant by-product, often face underutilization and resource wastage. This study aimed to explore the effects of partially replacing peanut vines (PV) in the diet with CS on the growth performance, rumen fermentation performance and microbiota, as well as the plasma physiology, biochemistry, and metabolism of Hu sheep. Twenty-seven 6-month-old male Hu sheep (weighing 39.4 ± 0.5 kg; mean ± SD) were randomly assigned to three groups: 1) basal diet (CON); 2) CS replaced 7.88% of PV (low substitution [LS]); and 3) CS replaced 15.57% of PV (high substitution [HS]). The feeding trial lasted for 91 d. Replacement of peanut vines with chrysanthemum stalks significantly increased dry matter intake in both LS and HS groups as compared to the CON group (P = 0.021; linear effect, P = 0.050), while average daily weight gain only increased significantly in the LS group (P = 0.020; quadratic P = 0.042). The concentrations of volatile fatty acids (VFAs) and ammonia nitrogen (NH₃-N) were the highest in rumen of LS group (P < 0.05; quadratic effect, P < 0.05). The LS group also had the highest relative abundance of Prevotella (P = 0.011; quadratic P = 0.001). The rumen metabolomic analysis showed elevated levels of flavonoids, terpenoids, and amino acids in the LS group (P < 0.05). Additionally, the LS group exhibited significantly higher levels of total antioxidant capacity, immunoglobulin A, and immunoglobulin M (P < 0.05; quadratic P < 0.05), while tumor necrosis factor-α and interferon-γ levels were lower (P < 0.05; quadratic P < 0.05). The plasma metabolomic analysis revealed increases in phospholipids, amino acids, and indole derivatives in the LS group (P < 0.05). In general, CS improved the growth performance of Hu sheep by increasing VFA concentrations and promoting beneficial bacteria like Prevotella in the rumen. Additionally, flavonoids and terpenoids in CS were positively associated with immune response and antioxidant capacity. These beneficial effects were more pronounced in the LS group compared to the HS group, highlighting the potential of CS as a roughage substitute for improving sheep growth performance and immune function.