The objective of this study was to evaluate the effects of supplementing monensin (MON:19.8 g/Mg DM TMR) and Saccharomyces cerevisiae CNCM I-1077 (LCY: Saccharomyces cerevisiae CNCM I-1077; 1 × 1010 cfu/hd/d) on lactation performance, feeding behavior, and total-tract nutrient digestibility of high-producing dairy cows. Sixty-four multiparous Holstein cows (3.2 ± 1.5 lactations; 97 ± 16 DIM, and 724 ± 68 kg of BW at covariate period initiation) and 32 gate feeders were enrolled in a study with a completely randomized design and a 2 × 2 factorial arrangement. Cows and gate feeders were randomly assigned to treatments (16 cows and 8 gate feeds per treatment). Cows were allowed 2 wk to acclimate to feeding gates followed by a 2 wk covariate period. During the acclimation and covariate periods, all cows were fed a diet containing MON and LCY. Following the covariate period, cows were enrolled in a 10 wk treatment period during which cows were randomly assigned to 1 of 4 treatments: 1) a combination of MON and LCY (MON-LCY), 2) MON alone, 3) LCY alone, or 4) neither MON nor LCY (CON-CON). Data were analyzed using a mixed model with week as a repeated measure and fixed effects of MON, LCY, week, and all their interactions. Cow (treatment) was included as a random effect. The average covariate period value of each variable was used as a covariate. Three-way interactions were observed for DMI and feed efficiency. Dry matter intake decreased from wk 4-5 and 8-10 in MON-LCY cows compared with CON-CON. No treatment differences were observed for actual or component-corrected milk yield or milk components, except for a tendency for LCY to decrease milk fat yield. Feed efficiency was greater for MON-LCY relative to CON-CON in 4 of 10 weeks. Interactions between MON and LCY were observed for dry matter and organic matter digestibility, where both were lower for CON-CON than other treatments. Under the conditions of the present study, feeding dairy cows in a high feed bunk density a combination of MON and LCY can decrease intake and improve feed efficiency without affecting milk production or components. Additionally, monensin and live-cell yeasts may each improve total-tract digestibility based on improvements in dry matter and organic matter digestibility.