Advances in prebiotics for poultry: role of the caeca and oligosaccharides

Prebiotics are non-digestible carbohydrates that selectively stimulate the growth of beneficial bacteria. Prebiotic supplementation into poultry diets results in a decreased rate of pathogenic bacteria colonisation in the gastrointestinal tract. It also enhances production of volatile fatty acids and lactic acid, which provide the bird with energy. This results in improved host gastrointestinal health and productive performance. Oligosaccharides are the most notable prebiotics in poultry nutrition. Examples of prebiotic oligosaccharides include xylo-oligosaccharides, fructo-oligosaccharides, and galacto-oligosaccharides. Oligosaccharides are derived from hydrolysis of non-starch polysaccharides (NSP). They are manufactured from plant sources, synthesised by physiochemical methods or enzymatic processes. The effects of oligosaccharides occur primarily in the caeca; oligosaccharides bypass the small intestine and reach the caeca, where they are readily fermented by beneficial bacteria, such as those in family Lactobacillaceae and Bifidobacteriaceae. Caeca function is generally poorly understood, despite extensive reviews and studies in this field. A deeper understanding of the factors that influence ability of the caeca to effectively utilise oligosaccharides is warranted. This would allow new prebiotic products and NSP- degrading enzymes to be developed, targeted to specific diets and scenarios. This is required, given the lack of consistency observed in the outputs derived from different studies assessing oligosaccharide efficacy in poultry diets. A key hinderance to progression in this field is that authors rarely analyse the oligosaccharide content and composition in the test diets and products, or in the bird's gastrointestinal tract. This review examines the mechanisms behind how oligosaccharides induce prebiotic effects in poultry, by identifying the role of the caeca in NSP digestion and identifying the impact of oligosaccharides on caeca microbiota and short-chain fatty acid composition.