Two trials were conducted to evaluate the effect of supplemental energy source and forage combination on performance, ruminal fermentation, and apparent nutrient digestibility. In trial 1, 41 lactating Holstein cows were fed a standardized diet (2-wk) and then assigned randomly to one of six treatments (4-wk). Treatments were arranged as a 2 x 3 factorial with two combinations of sorghum and ryegrass silage (50:50 or 75:25) and supplemented with one of three energy sources: ground corn, hominy, or a blend of ground corn and hominy. Trial 2: Three ruminally cannulated Jersey cows were used (3 x 3 Latin square design) to determine the effects of supplement energy source with the 50:50 ryegrass and sorghum silage base. Results indicated that a higher proportion of forage should be provided by sorghum silage than ryegrass silage when fed together. Source of energy supplement did not alter animal performance although ruminal fermentation was altered.