Abstract
This study evaluated the efficacy of Eucalyptus globulus essential oil (EEO) supplementation in attenuating ascites incidence and physiological disturbances in broiler chickens exposed to a cold-induced pulmonary hypertension syndrome model. A total of 720 one-day-old male Ross 308 chicks were randomly assigned to six dietary treatments, each with six replicates of 20 birds. The thermoneutral control group received a basal diet under standard conditions (32°C on day 1, gradually reduced to 23°C by day 20 and maintained until day 42; relative humidity [RH] 50-60 %), whereas the remaining five groups were exposed to cold stress (temperature reduced by 4°C/day from day 11 until reaching 15°C, then maintained at 10-15°C until day 42, RH 55-65 %) to induce ascites, and were fed the basal diet supplemented with 0, 500, 1000, 1500, or 2000 mg/kg EEO. Cold stress decreased body weight gain and feed intake and increased ascites-related mortality (P < 0.05). It also elevated erythrocyte count, hemoglobin concentration, and hematocrit, while reducing pO₂ and O₂ saturation and inducing right ventricular hypertrophy (P < 0.05). In contrast, inclusion of EEO in the diet linearly improved body weight gain, partially restored hematological parameters, and favorably modulated blood gas values compared with the unsupplemented cold-stressed group (P < 0.05). Cold stress also suppressed superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities in plasma and heart tissue, increased malondialdehyde (MDA) concentrations, and lowered plasma nitric oxide (NO) levels (P < 0.05). Dietary supplementation with EEO linearly increased SOD and GPx activities and plasma NO concentrations, while reducing MDA content (P < 0.05). Although EEO supplementation improved growth performance and physiological responses in cold-stressed broilers, values did not fully return to thermoneutral levels. Overall, these findings highlight the potential of EEO as a functional dietary additive to mitigate the adverse effects of cold-induced ascites and oxidative stress in broiler chickens.