Dear Charlotte

You don't say whether or not your area for the sheep has any shelter of any kind. They really do appreciate somewhere dry where they can get out of the wind and rain if it is really foul. Even a large open fronted pig arc will suffice.   The description of what you have available sounds reasonable but I would still be concerned about sheep standing out all winter on undrained clay. I would suggest that you try it out and see how they go but, if they don't have a field shelter on a dry base, be prepared to move them indoors if there is standing water on the pasture.

Feeding hay ad lib will be fine but they will also need a concentrate ration of some kind and a mineral feed bucket would also be a good idea.

Incidentally I don't know if you intend to mix sheep with the horses but be advised that we have found that this does not work if there is food around.   We have found that a greedy horse will kick sheep to keep them away from the food. We ended up having to put a ewe down who had been kicked and received a broken pelvis. We have never mixed sheep and horses since.

I hope this has been of some help to you.