ABSTRACT
The history of the application of mathematical models in the animal sciences has been reviewed.[1-4] Smith[5] developed a dynamic, mechanistic model of the metabolism of a lactating cow using the KINSYM modeling language of Garfinkel.[6] The model comprised mass action equations depicting individual metabolic processes, and was so large, unwieldy, and overparameterized that it was unstable and required excessive solution times on the computers available at that time. Several major benefits arose from the modeling effort of Smith.[5] The first was the collection and summarization of a great many data from the literature that have proven very useful to subsequent attempts to model ruminate metabolism. A number of the data summaries of Smith[5] were presented by Baldwin.[1] A problem arose during development of the data summaries that illustrates a benefit to research arising from the modeling process. They could not find data on organ and tissue weights in lactating dairy cattle in the literature. This required that these critical data be collected.[7] From this, the impact of changes in relative organ weights with changes in physiological state upon whole-animal energy requirements became apparent. This has since become a major focus in nutritional energetics.[8] This led us to our often-stated view that the modeling process aids in identification of critical experiments and that persons conducting modeling research must have the ability and resources required to collect critical data.[9-11] A second benefit was identification of significant gaps in our understanding of metabolism in adipose, liver,
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and mammary tissues of lactating dairy cows.[1] Another benefit was the initiation of efforts directed to the development of strategies for simplification and formulation of more stable models resulting in less expensive solutions.
