Yeasts are microorganisms that are an excellent source of bioactive compounds that have various nutritional and functional benefits to animals. Yeast products, particularly from Saccharomyces cerevisiae, have been one of the most commonly used feed additives for past decades in animal agriculture due to their beneficial effects on gut health and immune status. There are three main ways of feeding yeast products: live yeasts, yeast cell walls (YCW) and selenium yeast. This article aims to go in detail of the benefits of each type of supplementation.

Live Yeast

Live yeast products are most commonly associated with ruminants due to their positive effects on the rumen microbiome. One of the main challenges across all ruminant production is keeping the rumen at an optimal environment for appropriate fermentation and therefore proper cow health. An antagonist of this process is oxygen, which invades the rumen every time a cow eats or swallows her cud. As oxygen levels in the rumen increase, fermentation becomes sub-optimal due to the growth of aerobic (oxygen loving) bacteria in the rumen. Live yeast acts as an oxygen scavenger, consuming oxygen and converting to carbon dioxide, creating a more anaerobic (absence of free oxygen) environment that favors a heathier microbiome. This healthier microbiome helps to reduce the risk of ruminal acidosis and stabilizes rumen pH.
Live yeast has also shown positive effects on sow performance. Supplementation of live yeasts have shown to improve sow feed intake, milk production, colostrum quality, and litter weight at weaning (Tan et al., 2015; Domingos et al., 2021; Guillou et al., 2012; Sun et al., 2021). This is likely due to positive improvements in sow gut health with live yeast supplementation. The probiotic components of live yeast can work synergistically with healthy intestinal bacteria to strengthen the intestinal epithelium and enhance mucin production (Burdick et al., 2021), limit pathogen binding (Medzhitov and Janeway, 2000) and inhibit the proliferation of harmful pathogens (Liu et al., 2023).

Yeast Cell Wall

Yeast cell walls are composed of mannanoligosaccharides (MOS) and beta-glucans, both of which have positive effects on the digestive systems of livestock and poultry. The MOS in YCW act as a prebiotic, providing an energy source to the bacteria in the small intestine, aiding in improved nutrition digestion, promoting the growth of beneficial microbes, and reducing the risk of harmful intestinal diseases (Faber et al., 2012; Hashim et al., 2018). MOS have also been shown to improve villus height, crypt depth, and increase the number of goblet cells in broilers (Baurhoo and Ruiz-Feria, 2007).
Beta-glucans work hand-in-hand with the immune system, interacting with immune cells (macrophages, neutrophils, dendric cells) to produce cytokines that illicit specific and non-specific immune responses, leading to a system that is better able to withstand infection. Beta-glucans have also been shown to increase the expression of genes associated with adaptive an innate immunity (Tian et al., 2016). Notably, YCW supplementation has been shown to reduce colonization of salmonella and clostridium perfringens (Caly et al., 2015), leading to not only a healthier animal, but also a safer food supply. 

Selenium Yeast

Selenium is an essential trace mineral that plays roles in the reproductive and immune system. It has a major role in removing harmful free radicals in the body, as selenium is a main component of glutathione peroxidase (GSH-Px), which is the body’s main antioxidant. Selenium yeast provides a more bioavailable form of selenium to the animal in the form of selenomethionine. Selenomethionine is the most absorbable form of selenium as it can directly be incorporated into animal proteins and animal products, such as milk and eggs. Inorganic selenium, mainly in the form of sodium selenite, is poorly absorbed by animals and could lead to potential toxicity issues and environmental pollution as undigested selenium is excreted via urine.

Selenium yeast is produced by growing yeast in a high selenium medium. Yeast naturally contains the amino acid methionine, but the sulfur molecule is replaced by selenium in this process, creating selenomethionine. As a source of organic selenium, selenium yeast contains 63% selenomethionine, with the remaining 1/3 being in the form of other organic selenium compounds, mainly selenocysteine. 

Conclusion

Overall, yeast products are widely used feed additives that have numerous benefits across all animal agriculture. Live yeast products act as probiotics that stabilize the rumen and aid in gut health for all species, YCW products interact with the immune system to ensure animal health, and selenium yeast provides a bioavailable form of selenium for appropriate animal health and production.