Live yeast products have been proposed to increase nutrient utilization and milk production. Therefore the purpose of this trial was to determine if a live yeast product (LYP; BioCell 20, Phileo Lesaffre Animal Care, Milwaukee, WI) administered at 3g/cow/d to cows at a commercial dairy could increase milk yield and milk component production. All milking cows were milked 2 times a day and given LYP in the TMR in an OFF, ON, OFF, ON, OFF design where each ON or OFF period lasted 45 d and LYP was added to TMR during the ON periods only. Only data from cows that had at least one Dairy Herd Improvement Association milk test during each period remained in the data analyses (1903). Pens were fed the same respective diet (Fresh cow, milk cow, milk heifer or pregnant cow TMR) twice per day. Statistics were performed using Proc GLM (SAS Institute, 2013). To compensate for differences in days in milk (DIM) and milk production due to a period effect, treatment was nested within period, repeated measures for cow and covariates pen, DIM, diet, relative value, milk yield during period 1 (control period) and fresh date were included in the statistical model. There were no differences in least squares means of parity and small differences in least squares means DIM among periods. Average DIM in periods 2–5 were not different (P < 0.05; range 143- 298 d). Overall, daily milk yield (31.8 and 32.9.0 kg, P < 0.0001) and milk protein (1.02 and 1.08 kg, P < 0.0001; 3.25 and 3.31%, P < 0.0001) for control and LYP supplemented treatments, respectively, were higher for cows fed LYP. Therefore LYP did increase milk yield and milk protein kg and % but decreased milk fat % (3.71 and 3.60%, P < 0.0001), respectively.