Heat stress poses a major challenge to poultry production, emphasizing the critical need for efficient interventions to counter its negative impacts and support animal health and performance. The present study evaluated the efficacy of cinnamon nanoparticles in improving growth performance and alleviating heat stress in broiler chickens. A total of 500 one-day-old Ross 308 broiler chicks were randomly assigned to five dietary treatment groups in a completely randomized design. From day 1 to 25, broiler chickens were maintained under standard environmental conditions. Starting on day 25 until day 42, birds were subjected to daily heat stress exposure at 34 ± 2 ◦ C for 8 h per day (09:00–17:00). Each treatment included five replicates with 20 birds per replicate. The experimental treatments consisted of a control group receiving a basal diet without supplementation, and four groups supplemented with 150, 300, 450, or 600 mg of cinnamon nanoparticles (CNPs) per kilogram of feed. The CNPs were synthesized using an ultrasound-assisted method. Supplementation with CNPs significantly improved growth performance in a dose-dependent manner. Final body weight and body weight gain increased linearly, with the highest values observed at 600 mg/kg (2590 g and 1693 g, respectively) compared to control (1979 g and 1129 g). Although feed intake (FI) was numerically higher in the supplemented groups, the differences were not statistically significant across all levels. Feed conversion ratio improved significantly, decreasing from 1.73 in control to 1.40 at 600 mg/kg, while mortality rate was reduced from 10 % to 4 %. Antioxidant enzyme activities increased significantly with CNPs supplementation. Glutathione peroxidase and total superoxide dismutase activities showed linear improvements, reaching 229.91 mU/mL and 139 U/mL respectively at the highest dose, whereas malondialdehyde concentration decreased, and indicating reduced oxidative stress. Hematological indices were positively modulated; red blood cell counts increased significantly and white blood cell counts, heterophil percentage, and heterophil/lymphocyte ratio decreased, suggesting improved immune status and reduced physiological stress. Moreover, cecal lactic acid bacteria populations increased significantly with higher CNPs levels, while coliform counts remained unchanged. In conclusion, dietary cinnamon nanoparticles effectively mitigated heat stress effects in broilers by enhancing growth performance, antioxidant defenses, hematological health, and beneficial gut microbial, suggesting their potential as a natural feed additive in poultry production under heat stress conditions.
