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Summary: This study evaluated the potential of sumac seed powder (Rhus coriaria L.) as a natural feed additive to alleviate the detrimental impacts of high stocking density (HD) on broiler chickens. A total of 350 unsexed Arbor Acre chicks were randomly distributed into five groups. The control group was reared under normal density (ND; 10 birds/m²) and fed a standard diet, whereas the remaining groups were raised under HD conditions (15 birds/m²). Among the HD groups, one received the basal diet only, while the others were supplemented with 1, 2, or 3 g SSP per kg of feed. High rearing density markedly reduced growth rate, immune function, and antioxidant defense. However, SSP supplementation—especially at 2 and 3 g/kg—significantly improved live body weight, weight gain, and feed conversion ratio, with the 3 g/kg group showing performance values comparable to ND birds (P = 0.0021). Dressing percentage increased, while abdominal fat deposition declined. Birds receiving 3 g/kg SSP showed elevated hemoglobin, RBCs, and WBCs, and reduced serum glucose (P = 0.0039). Liver and kidney function indicators, as well as lipid profiles, were favorably affected, with reductions in total cholesterol and LDL levels (P < 0.05). Supplementation enhanced antioxidant capacity by increasing SOD, CAT, GSH, and TAC activities, while decreasing malondialdehyde and corticosterone concentrations. Immune competence improved, as shown by higher IgM, IgA, and IgY titers, greater relative weights of immune organs, and elevated lysozyme activity. Moreover, serum mineral concentrations (Ca, P, K, Cu, Fe) and tibia bone characteristics were enhanced. SSP inclusion also boosted digestive enzyme activities and positively modulated the cecal microbiota by increasing lactic acid bacteria and reducing pathogenic bacterial counts (P < 0.001). In conclusion, dietary supplementation with SSP, particularly at 3 g/kg, effectively mitigates the physiological, oxidative, and microbial stress associated with overcrowding, representing a promising ... |