Whenever I have seen what I call "feed rings" on one of my horses, it's always been one ring and is almost a change in color but, nonetheless it is a ring. Oddly enough this isn't the horse that foundered last March
It is, however, my horse that has severe allergies to oats/corn/soy, dust/mold, Spring & Fall. In other words life in general seems to affect him and it shows on his front hooves from time-to-time but it is not laminitis nor founder.
Founder rings are multiple on each hoof and wider at the back than in front.
This link may help you as it has pictures. Founder and Laminitis
Also there are some very wise and well-written Trimmers on this forum that hopefully will come in, to answer your questions better than I can.
If the horse is always dry lotted, the owners are really shoving it full of oats and hay for this to have happened.
Horses like this need frequent trims (every four weeks) but it sounds like that won't be happening either? The horse can't rehab itself, they have somehow got to understand it needs help, starting now.
Do you have a printer to where you could print off the key pages of the link above and show it to them?
This is the worst hoof on my foundered horse in December; 9 months after he foundered. He should not have looked this bad at this point in time but he was not getting handled properly by the people I hired to take care of his hooves. The wraps are on him due to one farrier cutting too much heel at one time and the result was torn ligaments & sesamoiditis; yes there are X-rays to back that up
The new Trimmers file those ridges down, to help retain integrity of the hoof as the ridges grow closer to the toe. The day this trim was done, the vet was here, along with the Trimmers. One thing this horse has in its favor is very thick and otherwise healthy wall. He does have wall separation from the founder but does not have White Line Disease because I monitor his hoof condition almost daily.
These hooves look a lot better today but this is pretty ugly isn't it -- the left hoof has the deepest dish; that is the hoof that rotated 8-9 degrees. It's a miracle the coffin bone didn't sink right thru the sole.