The nutritional requirements of a horse will depend on its age, stage of development, metabolism and workload. Hay alone will not meet the nutritional requirements of a young, growing horse, gestating or lactating mares or horses used for high levels of performance. However, high quality hay may well fill the requirement for a less active adult horse. Horses on strict hay diets do require a vitamin / mineral supplement. A mature horse will eat approximately two percent of its body weight on a daily basis, of which at least half should be roughage such as hay. Ideally, this amount of hay should be split into as many feedings as possible per day.