The horse is an herbivor, which means he only eats plant life, grasses mostly. If no grass is available they will need hay and some kind of grain to make sure they get all the nutrition they require....
A horse can eat many grains, grasses, and oats. But a horse cannot eat anything that has high fructose corn syrup, it would kill a horse. And NO Anomaly. This is what i saw on National Geographic....
Horse apples = manureYes, sometimes horses eat manure. This is called coprophagia. Foals start to eat manure at about two weeks of age. It is speculated that this is how they get good gut bacteria...