Abstract

Background: Heat stress (HS) is a major constraint to poultry production in tropical climates, partly through oxidative imbalance and disruption of intestinal homeostasis. This study evaluated whether a purple onion (Allium cepa L.)–Lactiplantibacillus plantarum synbiotic delivered via drinking water can mitigate HS-associated impairments in yellow-feather Rilai chickens.
Methods: A total of 144-day-old male chicks were assigned to 3 treatments in a completely randomized design (8 replicates/treatment) and reared for 80 days under natural HS conditions in an open-sided house. Ambient temperature and relative humidity were monitored and temperature–humidity index (THI) indicated sustained thermal challenge (monthly mean THI: 29.45–30.37). Treatments were: control (basal diet, T0) and synbiotic supplementation at 2 mL/bird/day (T1) and4 mL/bird/day (T2).
Results: Compared with T0, synbiotic supplementation improved growth performance in a dose-dependent manner, reducing feed conversion ratio (1.47 vs. 1.38 and 1.24; P < 0.05). Synbiotic birds exhibited improved redox status, evidenced by lower plasma malondialdehyde (0.77 vs. 0.48 and 0.40 nmol/mL) and higher superoxide dismutase activity (44.79 vs. 59.88 and 66.49 U/mL; P < 0.05). Intestinal ecology shifted toward a more favorable profile, with increased lactic acid bacteria and marked reductions in Escherichia coli and coliform counts in ileal and cecal digesta (P < 0.05). Villus height and crypt depth increased across small-intestinal segments, accompanied by reduced digesta pH (P < 0.05).
Conclusion: Overall, water-delivered purple onion–L. plantarum synbiotic supplementation improved performance, antioxidant capacity, and gut health indices in HS-exposed Rilai chickens, supporting its potential as a practical nutritional strategy during hot seasons.

Key words: Purple onion; heat stress; Lactiplantibacillus plantarum; synbiotic; Rilai chicken; antioxidant; gut microbiota