There are many things that can cause a line in the hoof... Stress is the big one; whether its stress from founder, a major weather change, serious illness (other than founder), or whatever might seriously stress your horse. Changes in feed can cause a ring to occur. Injury to the coronary band can cause a line to show in the hoof. Laminitis/founder also can cause the ring. I'm sure there are other things, but these are things I know of.MY mini Giddy has a line on his back hoof on the front. He acts fine and it made me wonder??
Giddy will be 2 in July... We have had alot of rain here .You definitely had something happen.
It kind of looks like a blow out but way too big.
Does not look like a founder line to me and it appears to be growing out just fine.
I sometimes see foals feet that look like this when they're growing out the baby hoof.
The other possibility could be damage to the periople area about 2 - 3 months ago.
Have you ever noticed the part of the hoof right at the coronery back looking white ?
The periople will look that way sometimes when we have a lot of rain and it is easier to damage at that time.
Do you see any thrush in the white line area at the toe ? You'll see separation right behind the hoof wall that has dirt packed in it. Check for that and it you do have separation treat with a good thrush remedy.
Doesn't look like anything to worry about to me.