A dynamic, mechanistic and deterministic model of feed intake regulation in dairy cows is described. The model is based on a conceptual model of feed intake regulation involving an interplay between rumen function and energy transactions. Two interconnected submodels are included, the rumen submodel (RS), adapted from a previously developed rumen model and the feed intake regulation submodel (FIRS). From RS rumen digesta load in terms of kg of NDF is calculated. FIRS not only describes the feed intake regulation but also the digestion, absorption and flow of nutrients beyond the rumen. Energy transactions in the model are related to the simulated difference between the capacity to use energy and the intake of metabolized energy. In the model, energy outputs of the animal include not only the energy needed for maintenance and milk production but also the energy needed to support a genetically determined time course of body reserves. Body reserves, both the absolute level and the rate of mobilization are considered in the regulation of feed intake. A preliminary evaluation of the model behaviour for a typical diet and animal inputs showed predicted values within expected values for feed intake, body condition score and body weight.