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Report, 1999

Extensions and refinements of the dynamic cow digestion model - Molly

Smårs, Sven


This thesis is composed of two parts. Part I deals with the extension and refinement of the cow digestion model Molly and Part II describes how the extended model was transformed into a more educational form. The purpose of Part I was to model the dynamics of the metabolic process from fodder to milk in the cow under Swedish conditions and under different management situations. After studying a number of models, it was decided to use the model "Molly" developed for U.S. conditions by Baldwin et al (1977; l987a,b,c). However, Swedish conditions differ from those in the U. S. in the sense that it is common practice in Sweden to schedule the feeding of forage and concentrate separately within a day. Separate parameters and facilities for scheduling the intake of four different feeds had to be included, A consequence of the more complex Swedish feeding conditions was that the model had to be extended to include four separate sets of physical and chemical feed descriptions instead of one. Therefore, parts of the rumen submodel were separated into four parallel submodels to allow for different degradation rates depending on source of feed. The structure and a description of the model from an overview down to essential details are also treated in this part. Finally, the differences in metabolism between the original U.S. Molly and the refined model under Swedish conditions were analysed in detail. In Part II, the purpose was to transform the extended model into a form which could be used for teaching and training. The reason for that was that the original model, written in the simulation language ACSL, is far too complicated to be handled for educational use. In operational terms the aims defined were: 1) The model must be hierarchically structured so that the whole process can be monitored and that the user can zoom into more detailed levels. 2) The model must be presented in a graphical form based on states and flows rather than in computer code. 3) Experimenting with the model by setting appropriate values to various parameters and initial conditions must be made in a user-friendly way without the need for entering programme code and recompilation. 4) The computer environment must support easy and flexible presentation of results in diagrams and figures. 5) The computer environment must have tools for handling pre-defined scenarios by using macro capabilities. MATLAB/Simulink was chosen as the best platform for the Molly digestion model in cow, mainly because of its graphical tools and its capacity to handle hierarchical structures. This part of the thesis also shows how to use the educational model.


cow model; cow simulation model; cow metabolic model; cow digestion model

Published in

Rapport - Sveriges lantbruksuniversitet, Institutionen för lantbruksteknik
Publisher: Institutionen för lantbruksteknik, Sveriges lantbruksuniversitet

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