The white line of the hoof is where the sole and the hoof wall meet:
Laminitis is a common cause of the white line widening (as the laminae die the hoof wall and sole move apart), this can lead to seedy toe or white line disease and infection can track up and cause abcesses. Instead of a neat thin white line you end up with a fibrillated looking wide line with long toe conformation.
Have very limited experience in that (now ex!) farrier said my old pony had it and took great chunks out of her wall. She did not have it, changed farriers and now all is well. I think it is treated with anti-fungal/bacterial sprays and can take a while to clear. Can make the hoof wall weak so prone to further breaking/splitting. Farrier said area needed to be opened in order to treat it and that she would need eggbars. Sounds like a doom- story doesn't it so wait till soemone who has proper experience of it comes on.
It really isn't a doom story. Barefoot owners are on the case of WLD the whole time, because so some extent we're more vulnerable as there is no shoe to cover the white line and grit can get embedded in it and start off a fungal infection.
But we are also better prepared to treat it as there is no shoe to get in the way. My podiatrist supplies a product called Cleantrax you dilute and soak for 45 minutes each hoof in a long soaking boot. The gravity of the water helps force the solution upward to reach the whole of the infection. You can do two hooves with one Cleantrax solution; after 90 minutes, it is inactive.
If you can't get Cleantrax you can use a 50% Milton solution, or Borax although I don't know the dilution.
I also have a product called Absorbine Thrush Remedy that I squirt round the white line periodically on a maintenance basis.
Rock had it mildly (enogh to make him lame) in the summer, was off for 2months but it cleared up well with the antibiotics and stuff i was given by the vet though its something i'll have to monitor all the time
My mare had it really bad. At first we did'nt know what was wrong, but her trot was terrible. The farrier suspected it, and was coming every four weeks to keep an eye on things.
One day when we tapped the hoof wall, it made that terrible hollow sound. We kept the hoof intact for as long as possible so that we could keep her shoes on.
Eventually the hoof had to be cut away, but we still managed to keep the shoe on. It has taken the best part of a year for the hoof to repair, and she has only been ridden since September.
My mare has had things wrong like this since the age of two, she is now seven and done nothing. I despair with her.
From all I have seen and heard about most horses when shoes are removed if inspected correctly would have this in some form or another.
It can be treated and treatmenst vary. From simple boraxing or hibiscrub and use of anti fungal treatments to something very good called Cleantrax.
But if on a shod horse it is near impossible to really get to the problem to treat.
Many have found one treatment works and another doesnt, we feel this might be due to differing water content and how it affects the product used.
I personally have my horse unshod and he has some WLD shown as small black spots along the white line. I wire brush after washing his feet with hibiscrub and then applying a athelets foot treatment balm all along the white line and this seems to be working as the black spots are going. I also cleantrax regularly approx every 3 - 4 months as my horse is still recovering from seedy toe from damage that the shoeing caused.
I would do a search on many of the BF web sites ie possible KC le Pierres web site for more information.
I am not selling you to BF only passing on what I have had experience of. I know my vet said the statement of most horses have it when inspected.