It depends how hard they are worked, but most do.
No because if it said The horses eat hay and grain then it would be a compound predicate:)
hay and grain Horses eat a varity of things. Grass, hay, grain etc
Horses primarily eat grass. hay, and grain.
Grain.
Grain, Grass, and hay, just like normal horses eat
How much grain a horse eats depends on how much work it is doing. Horses that do not do any work usually don't need any grain, just hay and grass. Some horses that are hard to keep weight on need grain, even if they don't do much work.
Hay,grain,and grass
Horses can eat chickpeas without any ill effect. Horses can eat almost any grain without consequence. Some horses do have preferences and will not eat all grains.
The same thing as other horses. Hay, grain, horse feed, etc.
Frequently exercised horses need extra minerals and grain.
Same as any other horse- grass and grain.
senior grain for horses provides the nutrients they need without as much fat because their bodies cannot metabolize it as fast.