_1786253245 20260809052725000 Rovedar Daryoushbabazadeh@gmail.com Rovedar Farm Animal Health and Nutrition Farm Anim. Health Nutr. 2980-7905 06 28 2026 5 2 Danladi Tsokwa https://orcid.org/0009-0009-4781-6932 Lawrence Anebi Ademu https://orcid.org/0000-0003-1806-8508 Rapheal James Wafar https://orcid.org/0000-0003-2125-1194 Jivini Aji Nwuku https://orcid.org/0000-0002-6888-8611 Aluor Adum https://orcid.org/0009-0005-3477-7875 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.   06 28 2026 11 16 https://creativecommons.org/licenses/by/4.0 10.58803/fahn.v5i2.121 https://fahn.rovedar.com/index.php/FAHN/article/view/121 https://fahn.rovedar.com/index.php/FAHN/article/download/121/139 https://fahn.rovedar.com/index.php/FAHN/article/download/121/139 10.1079/PAVSNNR201712031 10.1016/j.vetimm.2017.02.006 10.3382/ps.2010-00812 10.3382/ps.2013-03455 10.3382/ps/pey123 10.1093/jas/skaa090 10.3390/microorganisms13020257 10.1093/japr/13.1.86 10.1089/107999001317205123 10.3390/vetsci7030121 10.3390/ani3020356 10.1080/713654979 10.1016/j.scitotenv.2024.170410 10.1111/jpn.12041 10.1007/s00484-015-1103-x 10.1515/biol-2021-0031 Mamdooh AMA, Galib AMA, and Nihad AA. Role of yeast (Saccharomyces cerevisiae) as a source of probiotics in poultry diets. Eur J Mol Clin Med. 2020; 7(7): 6611-6617. Available at: https://www.ejmcm.com/archives/volume-7/issue-7/12167 10.1016/j.anifeedsci.2011.03.007 10.3390/ani12172297 National research council (NRC). Nutrient requirements of poultry. 9th ed. Washington, DC: National Academy Press; 1994. 10.13031/2013.12971 10.1175/JAMC-D-11-0143.1 Duduyemi OA, and Oseni SO. Modelling heat stress characteristics on the layers performance traits in South Western Nigeria. Tropentag. 2012. Available at: https://www.tropentag.de/2012/abstracts/posters/280.pdf 10.24880/meditvetj.1544695 10.3390/ani12151930 10.1007/978-1-4939-7802-1_9 10.1371/journal.pone.0280412 Fadanka S, Minette S, and Mowoh N. Preparation of bacteria glycerol stock. protocols.io. Available at: https://www.protocols.io/view/preparation-of-bacteria-glycerol-stock-b85iry4e SAS Institute Inc. JMP SAS Version 15.2. Cary, NC: SAS Institute Inc.; 2010. 10.1016/j.jtherbio.2022.103302 10.3168/jds.2008-1370 10.1016/j.livsci.2009.08.001 Ademu LA, Daudu OM, Iyeghe-Erakpotobor GT, Barje PP, and Olusiyi A. Betaine hydrochloride ameliorates thermoregulatory responses of broiler chickens under dexamethasone induced heat stress. Niger J Anim Prod. 2024; 2020(NSAP 2020 Proceedings): 659-662. DOI: 10.51791/njap.vi.4967 10.18689/ijbr-1000107 10.3390/poultry3020010 10.1007/s11250-025-04488-3 10.1093/jas/skz078 10.1590/1806-9061-2015-0180 10.5897/AJMR2013.6529 Buba W, and Shehu BN. Probiotic supplemented diet improved the gut morphology of broiler chickens. Niger J Anim Sci. 2018; 20(3): 67-72. Available at: https://njas.org.ng/index.php/php/article/view/1075 10.1093/ps/85.6.974 10.1111/j.1439-0396.2011.01187.x 10.3389/fphys.2018.01968 10.1590/1516-635XSPECIALISSUENutrition-PoultryFeedingAdditives099-104 10.1111/1574-6968.12293 10.3389/fmicb.2021.630841 10.1007/978-1-4939-0897-4_8 10.3390/nu12061769 10.1080/10408398.2020.1733483 10.3844/ajisp.2017.45.49 10.1101/cshperspect.a016295 10.5713/ab.21.0374 10.3389/fvets.2021.699081