Farm animals, as any living organism, need energy for their basal metabolism and physical activities.  When dietary energy intake exceeds energy expenditure (on a short-term or long-term basis), the surplus is stored, particularly in the form of glycogen and triacylglycerides.  The energy supply and need by the organism regulate the degradation and synthesis of these stocks.

Moreover, faced with environmental constraints (nutritional, health, heat, …), animal modifies the metabolism at cellular scale in order to guarantee its homeostasis. For example, in the case of nutritional challenges, the energy stocks are mobilized to produce the required energy for animal.

The objective of this study was to model the plasticity of the energy reserves at cellular scale faced with these perturbations. Several mathematical models have been developed to study the cellular metabolism based on different approaches: (i) topological analysis and flux balance analysis for a static description of metabolism and (ii) structural kinetic models and kinetic models for a dynamic description of metabolism [Ref].

A dynamic model has been developed to observe the evolution of energy stocks in a generic cell. In other words, based on regulators of enzyme activity, the dynamics of storage and use of these stocks in a cell have been described by mathematical equations.  Regulators of enzyme activity include the intracellular (ex. ATP/ADP ratio) and extracellular (ex. hormone secretions) signals. Metabolism of a muscle fiber and an adipocyte has been represented.  Indeed, the model, because of its generic aspect, can be used for other cell types by changing the basic parameters.

The model is based on a system of coupled ordinary differential equations. The numerical method is utilized to solve the model equations using free software Scilab.

The model is generic and phenomenological; however it provides a basis to investigate the relevant hypotheses in farm animal production. It allows for example studying the postprandial metabolism (fast dynamics) and energy stock management in lactation/gestation (slow dynamics).  Furthermore, it allows understanding and predicting the effects of diets containing contrasting sources of energy (carbohydrates / lipids) on the energy stocks in animal.

metabolism, system of ordinary differential equations, lipids, glycogen, enzymes regulators