An experiment was conducted on station, using a nested design in order to evaluate the effects of a Urea Molasses Multi-Nutrient Block (UMMB) supplementation of typical dry season, roughage based diets on the performance of mid lactating local Fogera and their F1 Holstein Friesian crosses in Ethiopia. Eight cows each from both breeds were assigned to a forage-based control diet and an experimental diet with UMMB supplementation. Highly significant differences were observed between treatments for most production traits. However, Fogera and crossbred dairy cows showed a different response pattern for some traits. Crossbred dairy cows were superior over Fogera for milk production, reproductive performance and benefit-cost ratio regardless of UMMB supplementation. Conversely, Fogera cows had higher milk solid contents and supplementing them with UMMB had a greater effect on milk fat than in crossbred cows. It is concluded that supplementing dairy cows with UMMB during the dry season is basically a helpful measure to maintain production. Depending on the availability of UMMB, priority in supplementation however, should be given to cows with a high genetic potential for milk production.