Practical application of the ME system in formulation of rations for both dairy and beef cattle is discussed. The ME system is based on a statement of the energy requirements of the animal for a given purpose, i.e. for maintenance, for a definite amount of growth or fattening, for the production of a specified quantity of milk of a given composition, or for work expenditure; and a list of feed values where each feed is assigned an energy value expressed in the same ME units as the stated requirements, i.e. MJ. The discussion on dairy rations covers formulation of winter feeding rations, concentrate feeds for milk production and complete rations.