As a herbivore adapted to taking in food continuously, the horse functions on a steady supply of small amounts of forage. In a natural environment it spends most of the day foraging, which provides not only a suitable supply of energy but also healthy function of the digestive system. Hydrochloric acid is produced in the stomach without interruption, whether or not there is food present. In practice, that means longer breaks in access to feed lead to discomfort and can encourage gastric ulcers. The observed need to take in feed therefore does not come from a lack of energy, but from the natural necessity of keeping digestion going.
Another reason can be too little fibre in the diet. Forage such as hay or grass plays a key role not only as a source of energy, but also as something that allows the digestive tract and behaviour to function properly. Enough fibre extends the time spent eating, stimulates saliva and steadies the environment of the large intestine. If a horse gets too little forage, and its diet is based on concentrates, it is left with an unsatisfied need to chew. That leads to growing frustration and to unwanted behaviour such as crib-biting.
The quality and composition of the diet matter too. Feeds that are poor in nutrients may not meet the body’s needs, so the horse instinctively tries to eat more. An excessive share of starch and sugars, on the other hand, can cause sharp swings in blood glucose and, as a result, unstable energy. A rapid rise in energy after concentrate is fed, followed by a fall, can be read by the body as a renewed need to eat.
The environmental and behavioural side also plays a key role. Limited opportunity to move, no chance to express natural herd behaviour, and long periods in the stable encourage frustration and stereotypies. In those conditions a horse often directs its activity towards looking for feed, which is wrongly read as constant hunger. In reality it is an attempt to compensate for what the environment does not provide.
💡FUN FACT: Dehydration can disturb the digestive system and be mistaken for hunger, so the horse should have constant access to fresh, clean water.
To sum up, a constant need to eat in horses comes from physiology, natural instinct and the conditions in which they are kept. What matters is constant access to forage, limiting any excess of starch and sugar, and creating conditions in which natural behaviour can be expressed. These are the things that leave the horse calmer and without the need to search for food all the time!