As rumen modifiers with distinct modes of action, yeast and phytonutrients may have additive effects on ruminal fermentation and animal productivity. To test this concept, an 8-wk, randomized complete block design study with 36 Holstein cows (average days in milk, 117 ± 37.5 d; average body weight, 651 ± 83.3 kg) was conducted to investigate the effects of a blend of phytonutrients alone or in combination with Saccharomyces cerevisiae-based yeast culture product on feed intake and milk production and composition. Cows were housed in a free-stall barn equipped with Calan Feeding System for monitoring individual feed intake. Following a 2-wk covariate period, cows were blocked in blocks of 3 based on days in milk, milk yield, and parity. Cows within a block were randomly assigned to one of the following treatments (12 cows/treatment): 14 g/cow/d yeast culture (YC), 1.0 g/cow/d phytonutrients (XT, a mixture of cinnamaldehyde, eugenol, and capsicum), and a combination of YC and XT (YCXT). Cows were fed ad libitum once daily. Treatments were top-dressed at the time of feeding. The basal diet consisted of (dry matter basis): 42.5% corn silage, 12.5% alfalfa haylage, 5.0% grass hay, and 40% concentrates and contained 16.3% crude protein and 32.4% neutral detergent fiber. Dry matter intake was not affected (P = 0.35) by treatment (29.1, 28.2, and 28.6 kg/d for YC, XT, and YCXT, respectively). Milk yield was also similar (P = 0.82) among treatments (42.3, 42.7, and 42.2 kg/d, respectively). Treatment did not affect feed efficiency (average 1.50 kg/kg; SEM = 0.030, P = 0.24) and concentrations of milk fat, true protein, and lactose (average 3.55, 2.98, and 4.84%; respectively; P ≥ 0.20). Concentration of milk urea nitrogen was also similar among treatments. In this experiment, there was no difference in lactational performance between cows supplemented with yeast culture or a blend of phytonutrients. In addition, additive effects of the 2 dietary supplements were not observed.