Evaluating Kleinia odora leaves as a novel phytogenic feed additive to enhance early growth, feed efficiency, European performance efficiency index, and carcass yield in broilers

• Broilers supplemented with 0.5 g/kg K. odora powder exhibited increases in body weight of 6.73% and 6.19% on days 14 and 24, respectively, compared to the control. • Broilers fed 0.5 g/kg K. odora showed an improvement in weight gain, FCR, and EPEF by 8.35, 7.75, and 17.01% during days 8-14 compared to the control. • Overall BWG and EPEF improved significantly by 6.35% and 12.31%, respectively, in broilers receiving 0.5 g/kg K. odora, indicating improved overall growth efficiency. • Feed intake remained unaffected in all treatments, suggesting that the increase in performance was due to improved nutrient utilization rather than increased consumption. • K. odora, particularly at a low dose (0.5 g/kg), enhanced lean tissue deposition and overall carcass yield while reducing abdominal fat, whereas higher doses (1.5 g/kg) showed opposite effects, highlighting both the benefits and limits of K. odora supplementation. Natural plant-based additives are increasingly being investigated in chicken production systems as safe and sustainable alternatives to synthetic growth promoters. This study investigated the effects of different dietary levels of Kleinia odora powder ( K. odora ) on growth performance, carcass characteristics, and the European Performance Efficiency Factor (EPEF) in broiler chickens. A total of 240 one-day-old broilers were randomly allocated to four dietary treatments, each supplemented with 0.0, 0.5, 1.0, or 1.5 g of K. odora per kg of diet, for a period of 24 days. Growth performance was evaluated weekly, while carcass traits were assessed at days 14 and 24. Results showed that birds fed 0.5 g/kg K. odora had significantly improved body weight gain (BWG), feed conversion ratio (FCR), and EPEF during days 8-14 and over the cumulative period, while feed intake (FI) remained unaffected across all treatments. At day 14, K. odora significantly improved breast and leg yields, especially at 0.5 g/kg. At day 24, birds fed 0.5 g/kg K. odora exhibited the greatest improvements in live body weight, carcass weight, and carcass yield ( P < 0.05), alongside a marked increase in breast yield and a pronounced reduction in abdominal fat ( P < 0.0001). Polynomial contrast analysis indicated significant cubic trends ( P < 0.002), confirming that moderate supplementation (0.5 g/kg) optimized carcass performance and lean tissue accretion while minimizing fat deposition. Higher K. odora levels (1.5 g/kg) increased liver yield, indicating a dose-dependent metabolic response. In conclusion, administration of 0.5 g/kg K. odora improved performance and carcass quality of broilers during the starter phase.