The use of live microorganisms as feed additives for ruminants is not a new concept. In particular, feeding livestock microbes is "useful" in large numbers under stress or disease challenges.
Microbial products used in this way were originally referred to as “probiotic” or “lifelong” products. The feed industry has used the more general term “microbial direct food” (DFM) to describe microbial feed additives. You can get more information about the best yeast for dairy cows via https://www.feedworks.com.au/
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From the research efforts, it is clear that supplementing with yeast products can beneficially alter the microbial, enzyme, and digestive functions of the rumen.
Studies show that viable yeast preparations can stimulate certain groups of beneficial bacteria in the rumen and provide a mechanistic model that can explain their effect on animal productivity.
Mushroom DFM has been a popular addition to ruminant diets for many years. In general, there are three types of mushroom supplements available. First, some products contain only live yeast (Saccharomyces cerevisiae) or together with its growth medium.
Second, other products contain S. cerevisiae and plant extracts, but do not guarantee living organisms. Third, there are fungal additives based on the fermentation end products of Aspergillus oryzae and Aspergillus niger, which also do not claim to supply live microbes.
The most commonly used yeast in the animal feed industry is Saccharomyces cerevisiae. It is usually given in milk rations to alter gastric fermentation, improve nitrogen digestion and absorption, reduce the risk of gastric acidosis, and increase animal productivity.