We have just moved and they have 40+ ac that they are grazing. The left there comfy lives about 3weeks ago so things have been a little different. However they have a salt and mineral block out and they are still getting oats at night.
It might be worth seeing what type of grass their on.... if its and old cattle station chances are its a grass with oxalates which could lead to the swelling.
I haven't had any dealing with the above mentioned problems as they are not common here. But if it gets worse and more facial bones begin to swell at least you will know what to do. :)