I've never had thrush problems either, and for a couple years my horses
stood in mud 24/7 during the spring. We still deal with mud, but they are
able to get onto drier land now. Cheers and Earen are unshod and Dezi is
shod during the ride season. Dezi and Cheers stay out all the
time, Earen comes in at night. I have also dealt with horses getting
thrush who are kept in pristine conditions. I wonder if there's as much a
genetic or conformational reason as a sanitary one.