Sorry I'm late to the party guys...
Thrush is caused by moist conditions, having mud packed in their hoofs.
She gets thrush in the middle of summer during a drought. Thrush doesn't just come when it's wet that's why I battle it year round.
I was hoping the cold would prevent it but I suppose she had thrush last February too....I've decided it's because I see my horse everyday to care for her that all this stuff happens to me.
My horse also had thrush this summer during the draught.
Everything was bone dry and he still had it. No one else did though.
I was frustrated and did some research on the various things to use and somewhere (I forget where) I found articles and data that showed high iron levels, as well as some other diet imbalences, could confound the issue and possibly set a horse up to have problems with it.
The data showed that raising the zinc and copper levels could be beneficial.
I live in a naturally high iron area (soils and water-despite filters too) and unknowingly had my horse on a vitamin supp with iron included.
I knew the iron was in it, but didn't know about the connection to the possible thrush issues with the hoof.
Anyway, in addition to using the various things to treat (I found the dry cow mastitis antibiotic cream to work the best initially) I switched my horse over to a hoof supp. Without added iron, but with higher levels of zinc and copper as well as higher biotin levels.
That seemed to really make a difference.