الفهرس 
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Abstract
Gut microbiome and immune response of chickens have been positively affected by feed additives such as probiotics and prebiotics under normal and heat stressed conditions. Climatic changes and elevated ambient temperature are environmental stressors that have a significant negative effect on birds’ physiological, behavioural, and immunological status, increasing their susceptibility to stress and immunosuppression and consequently increasing intestinal permeability (leaky gut). The present aimed to evaluate the efficacy of Bacillus spp. and lactobacillus spp. as probiotics as well as (mannan + glucan) as prebiotics supplements in experimentally induced heat stressed (HS) broiler chickens and study their impacts on birds’ performance, gut microbiome, and immune parameters.
Methods: A total of 240 one-day-old Ross broiler chicks were divided into eight groups (30 birds/group), and each group was subdivided into 3 replicates (10 birds each). The experimental groups were classified as follows; group 1 (G1): are the control negative; group 2 (G2): administered Bacillus probiotics without exposure to HS, group 3 (G3): administered lactobacillus probiotics without exposure to HS, group 4 (G4): administered (mannan + glucan) prebiotics without exposure to HS, group 5 (G5): birds were exposed to HS, group 6 (G6): administered Bacillus probiotics with HS, group 7 (G7): administered lactobacillus probiotics with HS and group 8 (G8): administered (mannan + glucan) prebiotics with HS. After vaccinations, blood samples were collected to evaluate the immune parameters of the chickens the in different groups. Fecal samples were also collected for the molecular evaluation of the gut microbiome based on the genetic analyses of 16S rRNA gene sequences.
Results: The results showed that HS has affected the chicken’s performance, and altered the gut microbiome, with observed variations in immune parameters. However, the addition of probiotics and prebiotics with or without stress improved performance, maintained a normal gut microbiome, and enhanced immune response.
Conclusion: Probiotics and prebiotics have a positive effects on the gut microbiome and the immune status of chickens under normal and heat stressed conditions, in addition to their efficacy as a growth promotor.
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