The objective of this experiment was to determine if lactational performance and energy partitioning by dairy cows would differ in response to dietary corn grain (CG) types [steam-flaked corn (SFC) vs. high-moisture corn (HMC)] and slow-release urea (SRU) supplementation. Eight multiparous Holstein cows (32 ± 8.2 d in milk) were used in a duplicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement to test four dietary treatments: SFC without SRU, SFC with SRU, HMC without SRU, and HMC with SRU. Supplementation of SRU tended to increase intakes of dry matter (DM) or increased crude protein (CP) intake under SFC, but no effect under HMC, leading to CG × SRU interactions on DM and CP intakes. Neither type of CG nor SRU supplementation affected milk production. The HMC fed at 14.3% DM allowed cows to partition more net energy into body weight (BW) compared with those fed SFC diets, whereas supplementing SRU tended to decrease the portion of net energy partitioned into BW gain under both SFC and HMC diets. These collective results demonstrate that feeding HMC with SRU can be a practical option in high-forage lactation diets to maintain or improve nutrient and energy utilization efficiency.