you are what you eat is the corect way to say it because if you eat something unhealthy then you are unhealthy and if you eat something healthy then you are healthy.
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....
because they have all the essantial needs in the food you eat what you eat to stay alive you can also eat just because of the way it tastes or to eat not because you want to or to stay alive but to...