Sheep, horses and rough grazing?

I have just bought a few fields for my horses and ponies. One of the fields is very rough with alot and i mean alot of rushes. Would this be suitable for grazing shetlands or would sheep be good or is it better to turn the land over and reseed ? Do sheep always have to be shaved or is there another animal that would eat the rough gr. Love the idea of sheep but would know alot about them or about shaving. Please give some good advice . Thanks