The aim of the review is to present mechanisms of digestion in horses through a functional description of the digestive system’s structure with emphasis on nutrient digestibility. In the era of an increasingly intensive and specialised sport usage of horses, also the significance of balancing their dietary nutrient value in accordance with individual requirements of these animals is gaining in importance. At the same time, it is not possible to meet nutritional requirements of a sport horse without knowledge about feed utilisation. In many farm animal species, digestibility is measured postmortem or via complicated and expensive cannulation of the digestive system. In horses, these methods are not applied due to ethical approaches or other limitations (e.g. sport horses); therefore, the importance of marker-based techniques is growing, although not much data is published in the available literature (Sales, 2012). Moreover, in contrast to other non-ruminants, horses are naturally adapted to a constant intake of large quantities of roughages. However, during intensive sport training, they are primarily fed concentrated diets with high amounts of easily digestible, non-structural carbohydrates and reduced amounts of dietary fibre fractions. Therefore, the risk of metabolic diseases and behavioural disorders in the horse increases.