In the dairy industry, cow health and farmer profits depend on the balance between diet (i.e., nutrient composition, daily intake) and metabolism. This is especially true during the transition period, where dramatic physiological changes foster vulnerability to immunosuppression, negative energy balance, and clinical and subclinical disorders. Using an Agilent microarray platform, the present study examined changes in the transcriptome of bovine PMNL, a representative cell of the immune system, due to time relative to parturition, prepartal dietary intake, or the combination. Sixteen Holstein cows were fed a high-straw, control diet (S; NEL = 1.34 Mcal/kg) or overfed a moderate-energy diet (M; NEL = 1.62 Mcal/kg) during the dry period. Blood for PMNL isolation and metabolite analysis was collected at −14 and +7 d relative to parturition. At an ANOVA false discovery rate (FDR) < 0.05, time (7 vs. −14 d) significantly influenced expression of 1758 genes, energy intake (M vs. S) influenced 3062 genes, and the interaction had an effect on 1673 genes. Dynamic Impact Approach (DIA) bioinformatics analysis classified effects on KEGG pathways, including: activated carbohydrate metabolism due to time and interactions, and activated amino acid (AA) biosynthesis and ribosome activity with dietary treatment. In contrast, DIA analysis revealed inhibition of riboflavin and fatty acid (FA) metabolism, unsaturated FA synthesis, and calcium reabsorption due to energy intake. These analyses suggest that processes critical for energy metabolism and immune function (e.g., calcium reabsorption, FA and vitamin metabolism, and AA synthesis) were affected by energy overfeeding with mixed results, but overall, strong effects from either main effect were mitigated by the interactions. Ingenuity Pathway Analysis (IPA) of genes significantly affected at an FDR <0.10 also revealed 50 upstream regulators for each main effect and interaction comparison. The widespread, transcriptome-level changes captured here confirm the importance of dietary energy adjustments around calving on the immune system.