Bacterial metabolites are crucial for the gut health of broilers through their impacts on the intestinal epithelium and immune system. Bacterial metabolites are produced in various parts of the digestive tract, with the crop, ileum and caeca being the primary locations. The production of microbial metabolites in broiler’s gut may be affected by intrinsic factors such as age, breed, and sex, as well as extrinsic factors such as nutrition and environmental conditions. Probiotics and phytobiotics are added in broiler diets to improve broiler health and performance by regulating gut microbiota and immune response. However, these feed additives may independently or in association with host-related factors show different impacts on metabolite production and immune responses in the broilers gut (Chapter 1).
Chapter 2 provides a summary of the literature on the effects of host-related factors as well as probiotics and phytobiotics on microbial activity and immune response in different intestinal regions of broilers.
Chapters 3 and 4 examine the effects of age (day 7, 21, 35), breed (Ross308 and Cobb500), sex (male and female), as well as probiotics (Bacillus based probiotics) and phytobiotics (grape polyphenols) on bacterial metabolite concentration, cytokine expression, gut morphology, and goblet cell count in the ileum and caecum of broilers. The overall results showed that age had remarkable impacts on all the measurements in the ileum and caecum, while breed, sex, and dietary treatments show only slight impacts on these parameters.
In conclusion, the present thesis demonstrated that the alterations in bacterial activity and immunological trait in the gut of broilers are age- and region-specific. The co-maturation of gut microbiota and immune system results in modification to the quality and quantity of bacterial- derived products as well as immune response during broiler growth. These changes in the ileum and caecum differed, which could be influenced by their distinct gut functions. Biological influences related to breed and sex as well as the supplementation of Bacillus based probiotics and grape polyphenols had a limited impact on bacterial activity and immunological traits, regardless of intestinal region. Future research is required to investigate the changes in gut microbial activity during broiler growth and to comprehend the underlying mechanisms of interactions between bacterial metabolites and gut immune system, which will elucidate the potential actions of these metabolites in influencing the immune system in the gut (Chapter 5).