I'm not sure on the reasons behind it because she does eventually lose it, so it's not cushings, her nutrition is pretty good her paddocks are well stocked with grass she always has a good quality salt/mineral block available, and she is wormed regularly.
I've started giving her baths and grooming her more often. Does anyone have any ideas?
She does grown an abnormally long and thick winter coat but that is the only thing I can think of that might contribute anything.