What are they?
The use of live micro-organisms as feed supplements for ruminants is not a new concept. Particularly, feeding large amounts of “beneficial” microbes to livestock under stress or confronted with a disease challenge.
Microbial products used in this manner were originally called “probiotics,” or products “for life.” However, the term “probiotic” implied a curative nature.
The feed industry, in conjunction with regulatory agencies, has accepted the more generic term of “direct-fed microbials” (DFM) to describe microbial-based feed additives. In addition, a list of accepted micro-organisms for use in animal feeds was developed.
Interest in the use of fungal direct-fed microbials in ruminant nutrition is considerable. The ban of antibiotic growth promoters in feed for production of animal foods in the European union has increased interest in evaluating the effect of yeast products on the gastrointestinal ecosystem, rumen microbial populations and overall animal performance.
Do they really work?
It is clear from these research efforts that yeast product supplements can beneficially modify microbial activities, fermentative and digestive functions in the rumen.
The research has demonstrated that viable yeast product preparations can stimulate specific groups of beneficial bacteria in the rumen and has provided mechanistic models that can explain their effects on animal performance.
Fungal DFMs have been popular additions to ruminant diets for many years. In general, three types of fungal additives are available. First, some products contain live yeast (Saccharomyces cerevisiae) only or associated with their growth culture medium.
Second, other products contain S. cerevisiae and culture extracts but make no guarantee for live organisms. Third, there are fungal additives based on Aspergillus niger and Aspergillus oryzae fermentation end products that also make no claim for supplying live microbes.