In its natural state, the horse is a nomadic animal, roaming up to 8-26 km/day and grazing for between 16 to 20 hours/day on a wide variety of plants. Its diet consists of typically low quality, high fibre feeds, and its gut has evolved to process this natural forage diet being taken in little and often. However, the environment of a domestic horse differs from that of a horse in its natural state. Horses are often kept stabled for large parts of the day with restricted access to grazing, with feeds being given in the form of meals and without free access to forage. Even pasture kept horses are unable to roam over wide areas and lack the variety of plants in their diets that a horse in its natural state would have access to.
Over the years our use of the horse has changed. With the mechanisation of agriculture came a move from the horse as a working animal to the leisure or sports horse and with this change of use, the types of feedstuffs used changed. The increased energy requirements of a sports horse, a racehorse for example, require the feeding of energy dense feeds such as cereal grains and would be unsustainable on a natural forage diet. While we have changed how and what horses are fed, their digestive system remains largely unmodified and this can lead to serious health implications and even death. To understand these implications we need to understand the Equine digestive system and its nutritional requirements.
The horse is classified anatomically as a non-ruminant herbivore. Non-ruminants, such as pigs, rely on enzymatic digestion with very limited fibre degradation occurring in the large intestine. In ruminants, such as sheep and cows the fibre degradation occurs in the rumen again with little fermentation in the large intestine. Horses lie somewhere between the two with enzymatic digestion taking place in the stomach and small intestine, together known as the foregut, and microbial digestion or fermentation taking place in the large intestine or hindgut.