The objectives of this study were to characterize the rumen microbiome throughout lactation and its association with gross feed efficiency in a cohort of Holstein cows. Rumen samples were collected using an oro-esophageal-ruminal sampling device (Flora Rumen Scoop; Profs-Product, Guelph, Canada) at d 7, 21, 50, 90, and 130 d postpartum in a cohort of 18 primiparous Holstein cows. Animals were housed in a barn with tiestalls fed the same diet during the entire study. Rumen samples 16S rRNA genes were sequenced using the MiSeq platform. The Shannon richness and diversity index did not change (P = 0.90) over time. The discriminant analysis did not show differences over time. The predominant phyla throughout lactation were Bacteroidetes, Firmicutes, Tenericutes, Proteobacteria, and Spirochaetes with mean relative abundance (MRA) of 43.0%, 40.9%, 3.4%, 3.4%, and 2.8%, respectively. The only change over time for phyla was an increase (P < 0.01) of the MRA at d 90 for the phylum Tenericutes that returned to normal at d 130 postpartum. The predominant genera were Prevotella, Butyrivibrio, Treponema, Shuttleworthia, Bulleida, Ruminococcus, RFN20, Clostridium, Coprococcus, and Fibrobacter with MRA of 25.7%, 3.8%, 2.7%, 2.3%, 2.3%, 2.2%, 2.2%, 1.8%, 1.6%, and 1.5%, respectively. The MRA for RFN20 was greater at d 50, 90 and 130 than in d 7 and 21 postpartum. Treponema tended to be increased at d 90 postpartum when compared with the other time points evaluated. Gross feed efficiency (GFE), calculated as energy corrected milk over dry matter intake, was categorized as Low <1.32 or High >1.32. Discriminant analysis revealed differences between Low and High GFE. Cows with high GFE had greater MRA for Bulleida (P = 0.02) and a tendency for greater MRA for Butyrivibrio than Low GFE. Also, Treponema MRA was lower in High GFE (P < 0.01) than Low GFE cows. The current data suggest that rumen microbiome is resilient throughout the lactation and cows categorized as Low GFE and HIGH GFE host a different rumen microbial population.