As horses have become more intensively managed over the past few centuries, it's become quite normal for most domesticated horses to receive grain as a portion of their diet. And while grain can have some benefits for some horses - those in heavy work, senior horses and pregnant mares for example - it should never be the majority of an equine's diet.
Why is this? We have to look to the way the horse was designed. Horses are grazers and physically designed to take in small portions of forage for a majority of the day - there is no difference in this between domesticated horses and their wild relatives. Rather than creating diets for our horses based on what has become normalized and what is convenient, we need to look to their actual physical needs and fulfill them accordingly. Read below for more reasons why it's not only important for horses to get enough forage, but potentially dangerous not to.
As always, if you have concerns about your horse's diet, contact your veterinarian or a qualified equine nutritionist.