A comparative evaluation of models of whole rumen function

A review is presented on the representation of various rumen fermentation aspects in whole rumen function models in relation to current knowledge on these processes, and areas in need of improved representation are highlighted. The importance of adequately stating the objective of the model in relation to the level of representation of rumen processes is stressed. No model yet exists which can accurately simulate rumen metabolism in all circumstances. A number of issues related to rumen modelling require further research. The sound representation of rumen microbial metabolism is essential. Aspects of microbial metabolism which deserve further attention include microbial distribution within the rumen, microbial interactions, and chemical composition of microbial matter. The representation of outflow from the rumen requires a more mechanistic approach, which should adequately cover continuous as well as discontinuous feeding regimes. Finally, the representation of VFA production is identified as being inadequate, and future attempts to improve prediction of VFA profile should include provisions for the effect of amount and rate of substrate degradation and microbial species preferences on type of VFA produced.