Impact of probiotic-supplemented water on the performance and physiological responses of broilers under normal and heat stress conditions.

Background and Aim: Heat stress (HS) significantly compromises broiler performance, intestinal health, and immune responses, posing a growing threat under climate change. Probiotics (PROs) have been proposed as a nutritional intervention to mitigate HS effects, yet their efficacy through drinking water remains understudied. This study aimed to evaluate the effects of water-supplemented PROs on growth performance, physiological responses, intestinal morphology, and inflammatory biomarkers in broiler chickens under thermo-neutral (TN) and HS conditions. Materials and Methods: A total of 192 one-day-old Ross 308 broiler chicks were randomly allocated to four treatment groups (6 replicates/group): TN with control (CON) water, TN with PRO-supplemented water, HS with CON water, and HS with PRO-supplemented water. PROs ( Results: HS significantly increased rectal temperature (Tr) (1.6°C; p < 0.01) and respiratory rate (57 breaths/min; p < 0.01). PRO supplementation reduced Tr by 0.17°C (p = 0.01) but did not affect performance metrics (feed intake, body weight gain, feed conversion ratio). HS reduced villus height (VH) and surface area in the jejunum and ileum (p < 0.05), while PROs partially ameliorated VH under HS. No significant effects of PROs were observed on serum amyloid A or tumor necrosis factor-alpha levels. However, PROs tended to reduce diamine oxidase levels (24%; p = 0.09). HS also decreased albumin and glucose levels (p ≤ 0.02). Conclusion: HS adversely affected intestinal integrity and selected blood metabolites. Although PRO supplementation had limited effects on performance and inflammatory biomarkers, it conferred modest thermoregulatory benefits and tended to improve intestinal permeability. Further research is warranted to optimize PRO formulation and assess synergistic strategies for HS mitigation in poultry.