Role of yeast cell wall polysaccharides in pig nutrition and health protection

Polysaccharides are the major components of the yeast cell wall and play multiple functions, ranging from the carriers of immunochemical specificity and marker molecules, by which cells recognize each other and interact with the environment, to the skeletal substances that define stability, shape, and morphology of the cell. In Saccharomyces cerevisiae, the two major polysaccharides, constituting up to 90% of the cell wall dry weight, are α-d-mannan and β-d-glucan, which have remarkable properties to interact with the immune system of the host. Modulation of mucosal immunity by the binding of these two polysaccharides to the specific receptors of immune cells provides beneficial effects on animal health and resistance to diseases. Specific commercial yeast cell wall polysaccharides supplied in feed (Bio-Mos®, Alltech Inc.) are able to block fimbriae of pathogenic bacteria, and thus prevent their adhesion to the mucous epithelium. Since adhesion presents the first step in microbial invasion, blocking of the receptors may prevent or eliminate infection. Yeast cell wall polysaccharides are also able to adsorb mycotoxins, thus decreasing their toxic effect and mediating their removal from the organism. Commercial yeast polysaccharides (MTB100®, Alltech Inc.) have been shown to absorb a wide range of mycotoxins at low inclusion levels. Thus, especially if the ban on antibiotic growth promoters becomes global, use of yeast polysaccharides as natural growth stimulators becomes a very urgent and rewarding issue.