No abstract

Empirical models relate nutrient inputs and outputs statistically, without considering the intervening metabolism of the animal (France and Thornley, 1984). Current rationing systems (e.g. ARC, 1980; Jarrige, 1988) are based on empirical models of energy and protein utilisation within the animal and do not enable prediction of responses to changes in nutrient inputs (Beever et al., 1991). Rook et al. (1990) had limited success in attempting to develop empirical regression models to describe the effect of nutrient input on milk constituent yields in dairy cows. The aim of the current study was therefore to use data from the literature to develop more appropriate empirical models that would allow the prediction of response in milk output and its constituent, to changes in energy intake.