Abstract
Pulmonary hypertension syndrome (PHS) in broilers, exacerbated by high-altitude and cold stress, leads to oxidative damage and intestinal dysfunction. Melatonin, with its antioxidant and anti-inflammatory properties, may mitigate these effects. This study examined how melatonin affects intestinal health and oxidative balance in broilers with PHS. We reared 108 broiler chickens at 2100 m altitude under cold stress and divided them into three groups: control, 20 mg/kg melatonin (Mel-20), and 40 mg/kg melatonin (Mel-40). Intestinal morphology, malondialdehyde (MDA) levels, and antioxidant gene expression (SOD1, GPX) were analyzed. Performance metrics and right-to-total ventricular weight ratio (RV:TV) were also assessed. Mel-40 increased body weight (P < 0.05), while both doses improved feed conversion ratio (P < 0.05). The Mel-40 group showed a lower RV:TV compared to the control group (P < 0.05). Mel-20 lowered MDA levels across all intestinal segments (P < 0.05), with large effect sizes in the duodenum (d = 1.41) and jejunum (d = 2.23). Mel-40 upregulated SOD1 in the jejunum and ileum and GPX in the ileum (P < 0.05), whereas Mel-20 increased both SOD1 and GPX expression in the duodenum and jejunum (P < 0.05). Villus height, width, and surface area increased in the duodenum and jejunum for both doses (P < 0.05). Melatonin supplementation improved intestinal health, antioxidant status, and performance in broilers with PHS under high-altitude and cold stress conditions. Optimal melatonin dosing depends on the therapeutic goal: 20 mg/kg for intestinal antioxidant protection versus 40 mg/kg for cardiovascular support.