Next the effect of the supplementation of two different yeast strains Saccharomyces cerevisiae in a diet on the milk yield, milk composition and health state of high producing dairy cows was examined. The 24 lactating dairy cows were allocated into three well balanced groups. Cows in the first experimental group were fed a supplement Biosaf Sc47 (B), cows in the second experimental group received a supplement Levucell 1020 (L) and the last group of the cows was a control group (K) without any supplementation of yeasts. All cows were fed a total mixed ration ad libitum. Dry matter intake, daily milk yields and the milk composition were recorded during the experiment. Although the addition of direct-fed yeast cultures in the ration of dairy cows did not increase the dry matter intake, there was a positive effect of yeasts on the increased daily milk yields when the group L produced in the average about 1.12 kg milk/day and the group B about 0.73 kg milk/day more than cows in the control group K.