Yeast cultures are also DFM and the most commonly used in swine diets include Aspergillus oryzae, Candida pintolopesii, Saccharomyces boulardii, and Saccharomyces cerevisiae. Yeasts are mainly used as live yeast cultures or yeast derivatives like yeast cell walls. The polysaccharides that constitute the yeast cell walls, notably β-glucans and α-mannans, are believed to be the primary reason for the effects of yeasts (Kogan and Kocher, 2007).
The exact mode of action and properties of yeast cell walls have not been fully understood but are believed to be related to improvements in resistance against enteric infections and modulation of immunity. Yeast cell walls appear to improve gut health by inhibiting colonization of enteric pathogens by blocking their binding sites in gut cells. Yeast cell walls also seem to enhance immunity by stimulation of immune cell function, upregulation of cytokines, and antioxidant activity (Kogan and Kocher, 2007). Another property of yeast cell walls is the toxin-binding capacity, which is mainly explored as mycotoxins adsorbents.
The effects of supplementing diets with yeasts and yeast derivatives on health and performance of pigs are ambiguous. There is evidence to support an improvement in resistance against enteric infections and growth performance of nursery pigs (Shen et al., 2009; Kiarie et al., 2011; Kiros et al., 2018), but these effects are often inconsistent (Liu et al., 2018). In grower-finisher pigs, the effects of yeast on performance have been unremarkable (Keegan et al., 2005; Kerr et al., 2013).