Enhancing growth, production, and public health in both animals and humans has shown significant promise when using probiotics and prebiotics either individually or in combination (synbiotics). Probiotics have positive effects on the host by restoring balance to the gut ecosystem and microbiota, enhancing nutrient digestion and absorption, mineral and vitamin biosynthesis, growth, production, and reproductive performance. They also improve the integrity of the epithelial barrier and enhanced antimicrobial activity by producing antibacterial substances, boost antiinflammatory properties and immunomodulatory effects. Probiotics are renowned for their ability to successfully combat enteric pathogens and lessen or prevent their negative effects on host growth, production, reproduction, and health. They are also helpful in ensuring that meat products are not contaminated with pathogens during processing and packing. The practical use of probiotics as a viable antibiotic alternative is justified by the growing public health concerns about the residual effects of antibiotics in animal tissues and products including meat, eggs, and milk, as well as the development of antibiotic-resistant bacterial strains. Promoting the potential use of probiotics in livestock, poultry, and fish would enhance their feed consumption and productivity, which would increase animal production and protect the health of both animals and consumers. On the other hand, prebiotics can alter the physiological processes in the chicken’s gut to enhance the health and performance of poultry. Prebiotics are organic additives to chicken diet that increase the nutritional value of birds by boosting growth rates, reducing mortality rates, and enhancing feed efficiency. Prebiotic action may have an impact on the breakdown of complex dietary compounds, the biosynthesis of vitamin and nitrogen compounds, facilitating the elimination of harmful substances from the diet. Prebiotics may potentially influence the host’s metabolism and immune system, while inducing favorable changes to the gut’s flora. It is important to note that bacteria of the gastrointestinal tract (GIT) convert the prebiotic substances into easily digestible organic substances. On the other hand, prebiotics positively affect biological processes of the GIT microbes. Prebiotics include any medication or feed additive that benefits the gastrointestinal microbiome. Their effects on the physiology and GIT microbes are discussed in this chapter, with a focus on how well chickens grow. Researchers, scientists, pharmacists, veterinary professionals, pharmaceutical industries, poultry and livestock industries will find in this chapter great value of updated information on the mechanisms of actions, positive aspects, and potential applications of prebiotics, probiotics, or synbiotics in animals, poultry, and fish. The gaps of information in these fields and potential research directions in the future will be highlighted in this chapter. © 2025 Elsevier Inc. All rights are reserved.