eng Rovedar Farm Animal Health and Nutrition 2980-7905 2026-06-28 5 2 11 16 10.58803/fahn.v5i2.121 123 Danladi Tsokwa 0 https://orcid.org/0009-0009-4781-6932 Lawrence Anebi Ademu 0 https://orcid.org/0000-0003-1806-8508 Rapheal James Wafar 0 https://orcid.org/0000-0003-2125-1194 Jivini Aji Nwuku 0 https://orcid.org/0000-0002-6888-8611 Aluor Adum 0 https://orcid.org/0009-0005-3477-7875 Department of Animal Production and Health, Federal University Wukari, Taraba State, Nigeria PMB 1020 Katsina-Ala Road, Wukari, Taraba State, Nigeria Introduction: Global warming increases environmental temperature, threatening poultry production worldwide. The present study aimed to explore the effects of yeast and Lactobacillus strains on gut health and immune parameters in broiler chickens under heat-stressed condition. Methods and materials: A total of 192 day-old Arbor Acre broiler chickens with average weight of 45 gr of both sexes were randomly divided into four treatment groups. Each group had three replicates of sixteen chickens in a completely randomized design, and intestinal morphology, microbial balance, immune response, and Temperature-Humidity Index (THI) were evaluated. Balanced basal diet were formulated and supplemented with no probiotic (control), Saccharomyces (S.) cerevisiae at 1g/kg (Sacc), Lactobacillus strains  (1010 cfu/g) at 0.25 g/kg (Lac), and a combination of Lactobacillus and S. cerevisiae (Lac-Sacc) at 0.25g and 1g per kg, respectively. Feed and water were provided ad libitum in a deep litter system for 42 days. Results: The THI data from the poultry house indicated that chickens were under severe heat stress during the experimental period. The results revealed that S. cerevisiae, Lactobacillus strains, and their combination significantly downregulated interleukin-6 (IL-6) expression and improved lymphocyte counts, with S. cerevisiae additionally upregulating IgM expression compared to control. Moreover, Lactobacillus supplementation positively affected villi height and crypt depth and lowered coliform bacteria compared to the control. Conclusion: The inclusion of S. cerevisiae and Lactobacillus significantly enhanced gut health in broiler chickens under heat-stressed condition, with Lactobacillus being more effective at alleviating heat stress.   https://fahn.rovedar.com/index.php/FAHN/article/view/121 Gut health Heat stress Interleukin Probiotic