Question: are you saying that this photo is AFTER a trim? is your horse a barefoot horse? if so, i would say those walls have been left a bit too long. of course it's hard to tell just from one photo. it looks like a "pasture trim" to me, which most or at least some "regular" farriers will do. a "barefoot" trimmer would take the walls down to nearly the level of the sole, if not all the way to the sole. maybe it's just a stretched white line from walls that are left too long? that is my guess. a pic of the hoof taken from the heel forward while holding the foot up and a pic of hoof on the ground would help to see if the walls are too long and the hooves are flaring at the bottom. that would indicate a stretched white line. maybe i'm crazy but again, hard to be sure with just this one photo. otherwise, those are nice hooves!