Evaluation of mechanistic rumen models to predict nutrients availability for grazing dairy cows on intensive production systems
From 1970 to date, significant progress has been made in the development of dynamic simulation models which provided the bases to integrate available knowledge, identify critical areas that would require future research and improve a quantitative understanding of the rumen function. There are still a number of limitations in the representation and quantification of key issues like distribution and interaction between the microbial population, passage of substrate out of the rumen and production and absorption of volatile fatty acids. The use of extant whole rumen models, to predict nutrient availability for grazing dairy cows, face additional limitation like the assumption of steady-state conditions, a constant fractional passage rate constant and uniformity through the day of the substrate chemical composition. Nutrient availability prediction for grazing dairy cows will require an integrated research of the ingestion – digestion process. Research programmes with a proper balance between modelling and analytical research, seems to be an effective strategy to improve both, understanding and quantification of the plant – animal – supplement interface.