I was picking out my horse's hooves today, and noticed this white chalky debris which easily came off. Parts of it were in chunks which looked like rocks at first. I lunged her and she was great, no lameness whatsoever. I've never seen this before which is why I was somewhat worried it could be a sign of thrush, although there was no odor or black on top over the white debris. The only thing over was some dirt.
Is this anything I should be concerned over?