With 55 acres of pasture, perhaps you can find someone who will cut it for hay for you. [You can pay straight up, but the usual is a split with you keeping part and the hay guy keeping part.] Just let it grow, have it cut (I think there are recommendations on the list as to the best time of day for cutting, or check the safer grass website, they probably have the info) and baled, then test it; if it tests good, use it for your horses, if it doesn't sell it and buy some that does.
And look into the pasture paradise tracks (think that's what they are called, basically a fence corridor around the pasture) for exercise.
Chanda
MT 9/04