Live yeast , autolysed yeast and yeast extract/metabolites are benefit for dairy milk yield in our experiment . but their mechanism is different.Live yeast can consume oxygen in rumen, reduce Oxidation-reduction potential.autolysed yeast provide protein(quick response), cell wall(immune response, absorbe some mycotoxin ),Vitamin (special in VB),flavor composition, enzyme,nutrients which stimulate rumen microbial growth .yeast extract/metabolites cell wall(immune response, absorbe some mycotoxin ),Vitamin (special in VB),flavor composition , increase DMI .One spares the function of others as probiotics.One can‘t spares the function of others as protein source.