Mechanistic models of nutrient digestion, absorption, metabolism, and growth are implemented in industry as ‘decision support systems’ for modern feed formulation and diet optimization, and in academia as research and teaching tools. However, in the equine sector, there has been little focus in modelling which limits the ability of the equine sector to address complex challenges such as interactions between equine nutrition, management, health and welfare. The aim of this proposal is to develop a mechanistic model of post-absorptive nutrient metabolism in mature horses.