Impact of diet-specific input parameters on simulated rumen function

Theories and concepts were investigated that have been applied in three extant models of rumen function by Baldwin et al., Danfaer and Dijkstra et al., as a preliminary step to investigate theories of intake regulation. These models are the most detailed at present and differed particularly in the description of microbial metabolism. Simulations were performed on inputs derived from seven experimental diets with very complete observations available of rumen dynamics. Comparison between models indicated that their simulation results differed markedly. In addition to daily feed intake and feed composition as model inputs, each model requires its own set of parameter inputs. However, some parameter inputs could not be estimated accurately from the available observations. The role of these unknown inputs on simulation results was studied by manipulating their estimated value. It was concluded that, in particular, parameter inputs whose concepts do not correspond to rumen observations have a large impact on model behaviour. Therefore, models need to be developed further to versions that use parameter inputs that can be readily estimated from rumen observations. The goal of the investigated rumen models is to simulate the chemical transactions inside and the nutrient release from the rumen. Nutrients absorbed after digestion seem to be important factors for regulation of daily intake. However, the models take daily feed intake as a known input instead of describing the regulation of intake, although it is highly unpredictable in practice. Thus, extant rumen models need to be developed and evaluated further before they can be used to investigate theories that go beyond the rumen compartment. (C) 1997 Academic Press Limited.