Join Date: Aug 2009
Location: secret mountain valley
Thrush can definitely pop up quickly, especially in conditions like you're having. There is not a lot of rhyme or reason to whether it develops in all 4 or just front, etc. unless there is an injury or weakness in a particular foot. Some horses seem to be more prone to it too, probably not something you did, or something a barn manager or something did, just something your guy gets and since you know how to treat it, no worries.
Although (and you didn't ask for advice so feel free to disregard this, just MHO) I think Koppertox and Thrushbuster are all fairly harsh chemicals that aren't totally necessary, especially if the thrush is not particularly bad. Apple cider vinegar, diluted and applied to clean hooves 1-2 times daily will clear it up as well. If you can get him out of the muck, all the better, but at the very least daily picking and treating and giving some "dry time" is the best way to treat thrush.