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 has increased interest
in evaluating the effect of yeast cultures (YC) on the gastrointestinal ecosystem, rumen microbial
populations and function. The effects of specific YC preparations on the rumen environment
and performance of ruminants have been well documented, and has generated considerable
scientific interest over the last two decades. The precise mode of action by which YC, which are
mostly derived from Saccharomyces cerevisiae, improve livestock performance has attracted
the attention of a number of researchers in the world. It is clear from these research efforts that
YC supplements can beneficially modify microbial activities, fermentative and digestive functions
in the rumen. The research has demonstrated that viable YC preparations can stimulate specific
groups of beneficial bacteria in the rumen, and has provided mechanistic models that can explain
their effects on animal performance. The effects of YC on animal productivity are strain-dependant.
So, all YC preparations are not equivalent in efficiency. This aspect opens a new field of research
for new strains, each being more specialized in its use. The goal of many of these research
activities has been to define the application and production strategies that can optimize animal
responses to YC supplements. Continuous research with live YC supplements has clearly
established scientifically-proven strategies for modifying and optimizing microbial activities in
the gastrointestinal ecosystem and techniques for improving performance and health of ruminants.
This article reviews the current status of the use of live yeast cultures in ruminant nutrition.