[Modelling of digestion in the rumen].

The ruminal ecosystem illustrates the main concepts of system analysis. Due to its structure and functional complexity and to its determinant role in ruminant nutrition and feeding, the reticulo-rumen has been the target of modelling works. The proposed models have been static or dynamic. The later have known a recent development but the former have until now largely contributed to the knowledge progress. The complexity of dynamic models is proportional to the number of biological mechanisms taken into account. The simplest models describe, for instance, a degradation or a transit elementary process. The aggregated models take simultaneously into account 2 to 4 processes while the general models aim at describing the digestive behaviour of the ruminal ecosystem by integrating its main functions. These mechanistic models have been studied for about 20 years. They are on the whole satisfactory but they are not sufficiently able to describe some diet differences and some variations in the dynamic properties of feed particles.