Sophora alopecuroides supplementation improves growth performance of Simmental cattle by enhancing feed utilization and regulating rumen bacteria community

This study examined the impacts of <i>Sophora alopecuroides</i> supplementation on growth performance, nitrogen (N) and energy utilization, methane (CH₄) emissions, serum indices, rumen fermentation, and bacterial community in Simmental cattle. Twenty-four 6-month-old male Simmental cattle (170.00 ± 1.07 kg) were randomly assigned to 4 treatments: control (basal diet, 0 mg/kg group) and basal diet with 150, 300, or 450 mg/kg body weight (BW) of <i>S. alopecuroides</i> supplementation. The 74-d trial included a 14-d adaptation and a 60-day experimental phase. Results showed that <i>S. alopecuroides</i> supplementation quadratically increased dry matter intake (DMI), average daily gain (ADG) and final BW (<i>P</i> < 0.05), while reducing feed conversion ratio (FCR) (<i>P</i> = 0.001). <i>S. alopecuroides</i> supplementation also quadratically increased the apparent digestibility of DM, organic matter (OM), neutral detergent fiber (NDF) and acid detergent fiber (ADF) (<i>P</i> < 0.05). Additionally, supplementation at 300 mg/kg reduced urinary N excretion and improved retained N, compared to the 0 mg/kg group (<i>P</i> < 0.05). <i>S. alopecuroides</i> supplementation quadratically enhanced gross energy intake (GEI) and energy balance (EB) (<i>P</i> < 0.05), while tended to quadratically increase digestible energy intake (DEI; <i>P</i> = 0.064), and metabolic energy intake (MEI; <i>P</i> = 0.087). Furthermore, the content of serum superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) were quadratically enhanced by <i>S. alopecuroides</i> supplementation (<i>P</i> < 0.05). Moreover, <i>S. alopecuroides</i> supplementation linearly increased the proportion of acetate in the rumen (<i>P</i> = 0.028), with trends towards a higher acetate/propionate ratio (<i>P</i> = 0.083) and lower concentration of propionate (<i>P</i> = 0.086). Alpha diversity indices (Chao1) were higher in the 300 mg/kg group than in the 0 mg/kg group (<i>P</i> < 0.05). <i>Rikenellaceae RC9-gut group</i> and <i>Ruminococcaceae NK4A214 group</i> were significantly increased in the 300 mg/kg group, and positively correlated with EB (<i>P</i> < 0.05); while <i>WCHB1-41</i> was decreased in the 150 and 300 mg/kg group, and positively correlated with UE and urinary N excretion (<i>P</i> < 0.05). The functional prediction results indicated that the pathways related to 'Xenobiotics biodegradation and metabolism', 'Biosynthesis of other secondary metabolites', and 'Infectious disease: bacterial' were significantly enriched in the 450 mg/kg group, while 'Pantothenate and CoA biosynthesis', 'C5-branched dibasic acid metabolism', and 'Valine, leucine and isoleucine biosynthesis' were significantly enriched in the 300 mg/kg group (<i>P</i> < 0.05). Co-occurrence network analysis revealed that <i>S. alopecuroides</i> supplementation at 450 mg/kg reduced the complexity and stability of the rumen bacteria network. In conclusion, dietary supplementation with <i>S. alopecuroides</i> at 300 mg/kg improved the growth performance of Simmental cattle by enhancing nutrient digestibility, N utilization, energy metabolism, and serum antioxidant levels. Excessive levels (450 mg/kg) negatively impacted the complexity and stability of the rumen bacteria community. These findings suggest that while <i>S. alopecuroides</i> can be beneficial at optimal levels, careful dose management is essential to avoid adverse effects on rumen microbiota and overall animal health.