A horse is a natural grazer, and for that reason their body is built to digest small amounts of food 24 hours a day. This includes the horse’s stomach, which is made to receive food on a continual basis.
That is why gastric acid production is also continuous. For a horse in the wild this function is incredibly useful, but for our domesticated horse, fed large portions on a few set occasions during the day, this continuous production of gastric acid that remains idle as it were inside the stomach, is not healthy and could cause serious problems.
