The Gut Microbiota of Laying Hens and Its Manipulation with Prebiotics and Probiotics To Enhance Gut Health and Food Safety

The microbiota plays a vital role in maintaining gut health and influences the overall performance of chickens. Most gut microbiota-related studies have been performed in broilers, which have different microbial communities compared to those of layers. The normal gut microbiota of laying chickens is dominated by Proteobacteria, Firmicutes, Bacteroidetes, Fusobacteria, and Actinobacteria at the phylum level. The composition of the gut microbiota changes with chicken age, genotype, and production system. The metabolites of gut microbiota, such as shortchain fatty acids, indole, tryptamine, vitamins, and bacteriocins, are involved in hostmicrobiota cross talk, maintenance of barrier function, and immune homeostasis. Resident gut microbiota members also limit and control the colonization of food-borne pathogens. In-feed supplementations of prebiotics and probiotics strengthen the gut microbiota for improved host performance and colonization resistance to gut pathogens, such as Salmonella and Campylobacter. The mechanisms of action of prebiotics and probiotics come through the production of organic acids, activation of the host immune system, and production of antimicrobial agents. Probiotic candidates, including Lactobacillus, Bihdobacterium, Bacillus, Saccharomyces, and Faecalibacterium isolates, have shown promising results toward enhancing food safety and gut health. Additionally, a range of complex carbohydrates, including mannose oligosaccharides, fructo-oligosaccharides, and galacto-oligosaccharides, and inulin are promising candidates for improving gut health. Here, we review the potential roles of prebiotics and probiotics in the reshaping of the gut microbiota of layer chickens to enhance gut health and food safety.