Effects of Dietary Menthol Supplementation on Growth Performance, Physiological Responses, and Immune Function in Heat-Stressed Broiler Chickens

Heat stress associated with climate change poses a significant challenge to poultry production, increasing interest in natural antioxidant phytochemicals as dietary mitigation strategies. This study evaluated the effects of dietary menthol on growth performance, physiological responses, and immune status in heat-stressed broiler chickens. A total of 90 Ross 308 broiler chicks were reared from 7 to 35 days of age and randomly assigned to three dietary treatments: a control diet and treated diets with two levels of menthol, 50 and 100 mg/kg. Each treatment consisted of five replicates with six birds per replicate, and feed was offered ad libitum throughout the experimental period. Dietary menthol supplementation significantly (p < 0.05) improved body weight gain at 21 and 35 days of age and reduced mortality compared to the control group. Feed conversion ratio was also significantly (p < 0.05) improved in menthol-supplemented groups, while feed intake was not significantly affected (p > 0.05). In addition, menthol increased (p < 0.05) serum total protein and globulin, reduced aspartate aminotransferase and alanine aminotransferase activities, and decreased (p < 0.05) uric acid levels, while elevating (p < 0.05) glucose, triiodothyronine, and thyroxine concentrations. These findings may suggest alterations in metabolic activity and liver-associated biochemical markers. From an immunological perspective, menthol augmented γ-globulin levels, immunoglobulin concentrations, innate immune activity, cellular immune responses, and interferon-γ production, demonstrating potential immunomodulatory effects. Ultimately, dietary menthol supplementation, particularly at 50 mg/kg, appears to be an effective natural approach for supporting growth performance, physiological responses, and immune competence in broiler chickens under heat stress conditions