Brewer's Yeast

• Byproduct of beer production
• Brewers select yeast for its fermenting ability and flavor
• Most strains used for fermented beverages are Saccharomyces cerevisiae, though specific strains are individual to brewers
• Most brewer’s yeast is dead, as a result of the brewing process

Dead Yeast

• Grown industrially and fed with its metabolites to supply nutrients, such as B vitamins and amino acids
• Uniqueness of each strain is not an important issue, because all dead Saccharomyces cerevisiae strains have a similar nutritional composition
• Dead yeasts have no remaining fermenting ability; little differentiation between products on the market
• Cannot reproduce in the rumen; is only a nutritional source for a limited time after feeding

Mineral Enriched Yeast

• Some companies use yeast to supply trace elements: selenium, copper, manganese and zinc
• Useful when small quantities of highly available mineral are used in a more targeted and effective way
• Yeast is grown on a mineral rich substrate; it incorporates the mineral into its own cell structure (e.g., selenium in this form is incorporated with the amino acid methionine into a natural form known as selenomethionine)
• Much more bioavailable to the animal, providing a more effective and targeted use of dietary selenium, with less risk of toxicity and environmental pollution