Effects of dietary garlic oil and black seed oil supplementation on growth performance, immunity, and immune-related gene expression in broiler chickens

Phytogenic feed additives encompass a broad category of plant-derived compounds that are used to improve animal health and production performance. Essential oils, as a volatile subclass of phytogenics extracted from plant materials, are recognized for their antimicrobial, antioxidant, and immunomodulatory properties and have been increasingly investigated as alternatives to antibiotic growth promoters in broiler nutrition. The study objective was to evaluate the effect of garlic and black seed oils on live broiler growth performance, immunity, and related gene expression. A total of 560 day-old Indian River broiler chicks were assigned randomly in a completely randomized design to one of four dietary groups, with each treatment consisting of 7 replicates (20 birds per replicate): control (CON; n = 140), garlic oil supplemented diet (200 mg/kg feed garlic oil, GO; n = 140), black seed oil supplemented diet (150 mg/kg feed black seed oil, BSO; n = 140), and the mixed oils group (200 mg/kg, 150 mg/kg for garlic and black seed oils, respectively, GO+BSO; n = 140). Supplementation with GO or BSO individually enhanced final body weight (p = 0.0356) and feed conversion ratio (p = 0.0407). White blood cell counts were lower in the treatment groups (p = 0.035). Serum triglycerides, VLDL, and AST levels were significantly reduced in the treatment groups (P < 0.05). Clostridium perfringens counts were lower in the treatment groups (p = 0.0006). Gene expression analysis revealed significant downregulation of pro-inflammatory cytokines (IL-6, IL-8, and TNF-α) and AvBD9, alongside upregulation of LEAP-2 and SLC11A1 in liver and spleen tissues. Dietary supplementation with garlic oil or black seed oil significantly enhanced broiler growth performance, lipid metabolism, immune function, and gut microbiota balance. The combined treatment (GO+BSO) did not produce additive or synergistic effects, suggesting overlapping mechanisms of action. These findings support GO and BSO as effective multifunctional alternatives to antibiotic growth promoters in sustainable poultry production.