A REVIEW OF EMPIRICAL AND MECHANISTIC MODELS OF LACTATIONAL PERFORMANCE BY THE DAIRY-COW

Current feeding systems for dairy cows are based principally on metabolisable energy and aim to meet calculated energy requirements. They do not predict milk composition or the response of the animal to changes in nutrient inputs and are thus inadequate in the current situation of production quotas and payments based on yield of milk constituents. Models which include the digestive and metabolic fate of individual nutrients, while providing as simple a representation as possible, therefore need to be considered. Models may be empirical, that is relate input to outputs without consideration of the intervening metabolism, or mechanistic, that is the response of the whole animal is simulated by the representation of individual tissues. These different approaches to modelling are considered, reviewing progress made to date, highlighting current inadequacies and discussing the future potential of these approaches. Empirical and mechanistic representations of the lactation curve, that is of the time course of lactation, are first considered, followed by empirical and mechanistic models of the response of the cow to dietary inputs. Finally future research needs are discussed in the light of the changed circumstances in the dairy industry.