Horses were born to eat grass, it is their natural food. The supplemental feeding of grain was created by man in order to keep weight on horses as they were being used for beasts of burden. Horses pulling caravans across this vast country did not have time to graze, so man had to supplement their need for food. This is probably when feed bags were invented. As man settled and began to farm, horses were necessary for plowing and traveling long distances either for supplies or for herding cattle; again demonstrating the need for grain.
Horses can survive on grass alone. The need to give them grain will depend on the age of the horse, what kind of activity the horse is performing on a daily basis, the amount of pasture that is available for the individual and the quality of the pasture. Young horses that are weanlings (babies just weaned from their mother) and yearlings are growing at a fast pace. Actually any horse under the age of five for most breeds is still growing. If you want a horse that is strong and will grow to their full potential, giving them grain is the right thing to do. Horses that are being ridden often or on a daily basis should have grain. Now if your horse is in a pasture that has a lot of weeds or the grass stays short because there are too many horses in one pasture, then you may also want to supplement them with hay as well as grain. Another factor that comes into play is the breed of the horse. Certain breeds will need only a small amount of feed, others such as Thoroughbreds, need much more grain to accomplish the development of a healthy, strong animal.
Being a horse owner means that you must monitor your horses weight and condition constantly, whether they are in a stall or in a pasture. If you have a horse or pony that is an aggressive eater and is becoming too fat or even obese, when you are graining the other horses in the pasture, you will have to put that horse in a catch pen, usually built into a corner of a pasture, with no grain until the other horses are finished eating. Remember, if you are giving grain to pasture horses, the amount that you feed will be much less than that of winter time. Lets’ say you turn your horses out during the day in the winter. They will just forage around and pick a little on old dead grass that has little to offer as opposed to gorging themselves all day long and even during the nighttime. Horses can suffer from a severe condition called laminitis (founder) when they are carrying too much weight and producing too much heat in their bodies, and the heat travels to their feet. This condition is not only very painful for the horse but it is a permanent condition. They become more sensitive, can re-founder, will need extra care and specialized shoeing, and it can even cause them to loose their life if they are not removed from the environment that originally caused them to founder.
Horses have been around for millions of years and they survived without grain. The decision is yours and if you have horses in a rich pasture and they are not being ridden often and they have a healthy weight on them, then grain probably is not necessary. As long as your horse has a plentiful supply of rich grass, plenty of fresh water, trees or woods or a lean-to structure for protection, and you have them on a regimented worming program (will be discussed at a later date), life will be good for them without grain. Even though they seem to be self sufficient, horses always need to have a watchful eye on them at least once a day. It is necessary to check their water and clean the waterer or tubs often. Make sure all the horses seem happy, and are following their usual daily habits. You must also check them thoroughly making sure there are no serious cuts, wounds, or kick marks, and check their eyes for injuries or signs of illness or allergies.