The incorporation of direct-fed microbials (DFM) into dairy cow diets may enhance overall lactation performance. In this study, a novel blend of probiotics was added to the diet of Holstein cows to modify the rumen microbiome, and changes in energy balance and milk quality were evaluated. Ten cows in early lactation, blocked by their days in milk, were assigned to one of 2 groups (control or DFM, n = 5). All cows received the same basal diet during a 14-d acclimation period. On Day 15, the DFM group diet was topdressed with calf grains mixed with a blend of probiotics at 5 g DFM per cow per day (Pediococcus acidilactici, >1.0 × 10⁸ cfu/g; Pediococcus pentosaceus, >1.0 × 10⁸ cfu/g; Lactobacillus plantarum, >1.0 × 10⁸ cfu/g; Bacillus subtilis, > 1.0 × 10⁷ cfu/g). The control group diet was topdressed similarly, but without probiotics. The cows remained on their respective treatment diets for 21 d, followed by a 14-d transition period in which both groups returned to the same basal diet. Blood and milk samples were collected weekly during the trial (on d 0, 7, 14, 21, 28, 35, 42, and 49). Data were analyzed by the t-test with statistical significance indicated by P < 0.05. There were no differences in blood serum β-hydroxybutyrate or nonesterified fatty acids between the 2 groups at any time points. For milk quality, there were no differences in fat content, protein content, somatic cell count or urea nitrogen. However, on d 35, both lactose content (5.08 ± 0.06% vs. 4.79 ± 0.07%; P = 0.024) and solids-not-fat (8.98 ± 0.16% vs. 8.28 ± 0.09%; P = 0.009) were significantly higher in the DFM group compared with the control. These increases were not observed after the cows returned to the basal diet. Preliminary data obtained by analyzing the rumen fluid DNA from 4 cannulated experimental cows showed a small but significant change in the rumen microbiome (P = 0.017) on the family taxonomic level from d 28 to 42. Our results suggest that a novel blend of probiotics could mildly modify the rumen microbiome, but any resulting effects on milk quality are transient. Further investigations on milk production and underlying factors on the increase in lactose are highly warranted.