They won't [shouldn't] get thrushy from having a mud spot they visit, like near the water trough, when it's super dry out. Up here in the NW, we ~really~ know how to grow fungus!
They get fungus when their feet are wet ALL the time, standing in mud, no dry spots, never a chance to dry out completely. Part of the good in letting them in stall when it's wet outside is to let their feet dry out and harden again every day. They get soft in wet, just like our nails do in a bath.
But Bay hasn't gotten thrushy yet, even in pads that might act to trap moisture.