Dose-dependent effects of dietary olive leaf powder on growth, hematobiochemical indices, antioxidant capacity, immunity, cecal microbiota and economics of Japanese quail

This study investigated the dose-dependent effects of dietary olive leaf powder (OLP) on growth performance, carcass traits, hematobiochemical parameters, antioxidant capacity, immune response, cecal microbiota, and economic efficiency in growing Japanese quail. A total of 400 one-day-old quails were randomly assigned to five dietary treatments, including a basal diet without supplementation (control) and four diets supplemented with OLP at levels of 1.0, 2.0, 3.0, or 4.0 g/kg feed for six weeks. Quails receiving 3.0 and 4.0 g/kg OLP exhibited significantly higher live body weight (LBW), body weight gain (BWG), and improved feed conversion ratio (FCR) compared with the control group. Carcass yield and dressing percentage were favorably enhanced in quails fed 2.0 and 4.0 g/kg OLP. Dietary OLP supplementation positively modulated hematological and biochemical indices, as evidenced by increased hemoglobin concentration, erythrocyte and leukocyte counts, and globulin levels, along with reduced heterophil-to-lymphocyte (H/L) ratio, alanine aminotransferase (ALT) activity, triglycerides, total cholesterol, very-low-density lipoprotein (VLDL), and low-density lipoprotein (LDL) levels. Antioxidant status was markedly improved in OLP-supplemented groups, as indicated by elevated superoxide dismutase (SOD) and glutathione (GSH) levels and decreased malondialdehyde (MDA) concentration. Immune response was enhanced through increased circulating immunoglobulin levels. Furthermore, dietary OLP favorably altered cecal microbial populations by reducing total bacterial count, coliforms, and Escherichia coli , while increasing lactic acid bacteria in a dose-dependent manner. From an economic perspective, OLP inclusion improved productive efficiency and maximized economic returns. Overall, olive leaf powder can be considered a promising natural feed additive for improving growth performance, health status, gut microbial balance, and economic efficiency in growing Japanese quail.