Evaluation of betaine as a nutritional strategy to counteract cyclic heat stress in broilers: Performance, behavior, blood biochemistry, and tissue integrity.

This study aimed to investigate the effects of betaine supplementation on performance, behavior, carcass characteristics, blood biochemistry, and immunohistochemistry of key organs under heat stress. One hundred twenty broiler chicks were randomly assigned to four groups (6 replicates of 5 chicks each) across two climate-controlled units. The groups included: G1, the control; G2, control with betaine; G3, heat-stressed; and G4, heat-stressed with betaine. All groups received a standard broiler diet, with 1 g/kg betaine added to groups 2 and 4. Heat stress negatively impacted performance, decreasing final body weight by 6.94% and weight gain by 7.25% in heat-stressed birds. Nonetheless, betaine supplementation notably increased final body weight (P < 0.05) in both normal and heat-stressed birds by 13.07% and 12.12%, respectively, and increased weight gain by 13.39% and 12.61%, respectively. Carcass characteristics were not affected by heat stress or betaine. Under heat stress (P < 0.05), behaviors such as feeding, foraging, walking, standing, and comfort decreased, while lying and drinking behaviors increased. Notably, betaine supplementation mitigated these shifts, restoring normal behavioral activity. Betaine enhanced physiological responses (P < 0.05), increasing serum levels of total protein (5.18%, 4.63%), albumin (2.06%, 1.445), total antioxidant capacity (13.41%, 11.46%), and superoxide dismutase (158.59%, 144.15%) in both normal and heat-stressed broilers. It also decreased total cholesterol, triglycerides, malondialdehyde, and inflammatory markers (P < 0.05). Histological and immunohistochemical analyses of the liver, intestine, and bursa revealed adverse effects of heat stress, but betaine supplementation partially alleviated the damage. Profitability improved with betaine in both environments, increasing net revenue and economic efficiency by 35% and 26% under normal conditions, and by 23% and 12% under heat stress, respectively. Betaine supplementation may mitigate the adverse effects of chronic cyclic heat stress in broilers by modulating immune and antioxidant defenses, reducing pro-inflammatory markers, and preserving intestinal tissue integrity.