To understand the mechanism by which microalgae supplementation improved the redox system, we analyzed the expressions of several antioxidant-related genes in the ileum. stress + 3% microalgae (HS+MAG). The broilers in the HS+MAG group were fed a diet supplemented with 3% microalgae, whereas NHS and HS groups were fed a standard broiler diet. Broilers in the NHS were raised under standard temperature (20C24C), while HS and HS+MAG broilers were subjected to cyclic heat stress from d 22 to 35 (32C33C for 8 h). Heat stress significantly decreased the final body weight, whereas the supplementation of microalgae increased the final body weight of broilers (P< 0.05). The expressions of ileal antioxidant (GPX3), immune-related (IL4), and tight-junction (CLDN2) genes were increased in microalgae-supplemented broilers compared to heat-stressed broilers (P< 0.05). The ileal villus height to crypt depth ratio was improved in microalgae-supplemented broilers (P< 0.05). In addition, microbial alpha, and beta diversities were higher in the HS+MAG group compared to the HS group (P< 0.05). There was an increase in volatile fatty acid-producing bacteria at the genus level, such asRuminococcus, Ocillospira, Lactobacillus, Oscillobacter, Flavonifractor, andColidextribacterin the group that received microalgae supplementation. In conclusion, dietary supplementation of microalgae improved the growth performances of heat-stressed broilers by improving their physiogenomics. Thus, the dietary inclusion of microalgae can potentially mitigate heat stress in ISX-9 broilers. Key words:broiler, heat stress, microalgae, antioxidant, health == INTRODUCTION == The world’s population is growing exponentially, causing a rise in demand for animal-based protein. To meet the meat demand, broiler chickens have been genetically selected for higher feed efficiency and high muscle yield. As a result, these broiler chickens produce a high amount of metabolic body heat and are highly susceptible to warmth stress (HS), especially during the summer. Moreover, chickens lack sweat glands and have feather covers, which make them extremely sensitive to warmth stress. Exposure to warmth stress disrupts the thermoregulatory mechanism of chickens, leading to an imbalance in their physiological redox status. Consequently, warmth ISX-9 stress can adversely effect broilers health and production. Therefore, the increasing environmental temperature during the summer season and amid global warming is an apparent concern of the poultry industry, leading to warmth stress and severe economic loss (Wasti et al., 2020). To combat the harmful effect of warmth stress on chickens, various nutritional, managemental, and genetic strategies have been implemented (Saeed et al., 2019;Abbas et al., 2022). Mitigating warmth stress using managemental and genetic strategies is definitely expensive and time-consuming. Consequently, reducing the effect of warmth stress in chickens is more viable by software of nutritional ISX-9 strategy which entails phytochemicals, probiotics, prebiotics, vitamins, and minerals. Phytochemicals, such as antioxidants, antibacterial, antiviral, and antineoplastic, are becoming increasingly popular and have health remedial action in heat-stressed poultry (Kumar et al., 2021). It is of utmost importance to develop a sustainable strategy for the poultry industry to combat warmth stress. Thus, exploring fresh feed health supplements with warmth stress-alleviating practical properties is definitely critically necessary. Microalgae (Spirulina platensis) are sustainable sources of energy and are available commercially across the world. Microalgae are filamentous photosynthetic cyanobacteria abundant in protein (65%), carbohydrates (25%), essential fatty acids (18%), vitamins, and minerals (Brito et al., 2020;Pestana et al., 2020). In addition to nutritional abundancy, microalgae will also be rich in practical bioactive compounds such as phycobiliproteins (-phycocyanin and C-phycocyanin), -carotene, phenolic acid, flavonoid, -linolenic acid (Farag et al., 2016;Wu et al., 2016). Microalgae also possess alkaloids, glycosides, tannins, steroids, and ISX-9 saponins (Zeweil et al., 2016). These biomolecules are associated with several health benefits in humans and animals and act as; scavengers of reactive oxygen varieties (ROS), reactive nitrogen varieties (RNS), inhibitors of neoplasia, inflammatory mediators, and suppressors of pathogenic bacteria (Dillard and German, 2000). Microalgae supplementation in the diet improves the production of important antioxidant enzymes and confers cellular safety (Mirzaie et al., ISX-9 2018;Liu et al., 2021;Moustafa et al., 2021). However, the part of microalgae in health and production, along with the underlying mechanism in heat-stressed broilers, is not completely explored. Based on the biochemical properties and health benefits of microalgae, we hypothesized that supplementation of microalgae to heat-stressed broilers’ diet might improve growth performances by influencing underlying health-associated mechanisms. Consequently, this study targeted to investigate the effect of microalgae DNAPK supplementation in broilers diet programs on underlying gut health parameters (manifestation of antioxidants, warmth shock, immune, and tight-junction genes), ileal histomorphometry, volatile fatty acid production, cecal microbiota,.