The white line of the foot can be seen by looking at the sole of your horse’s hoof. The area (that looks whitish) between the outside hoof wall and where it meets the sole is the white line. When this becomes damaged, it allows fungus and/or bacteria to invade and separate the layers of the hoof wall. When that happens, the infection can spread around the hoof and up the inside of the wall to gradually “eat away” at the hoof, making a horse very lame.

White line disease is actually a misnomer, as the white line is not actually involved, but rather the deepest layer of the non-pigmented stratum medium. White line disease has many other names: stall rot, hollow foot, wall thrush, and seedy toe. For ease of our discussion in this article, we’ll refer to this problem as white line disease.

What You See

White line disease is characterized by progressive hoof wall separation that occurs in the non-pigmented horn of the hoof at the junction between the stratum medium (middle layer of the hoof capsule) and laminar horn. The separation is usually progressive, and it typically involves the toe and quarters of the hoof.

“Back 10-15 years ago, every time you would open a magazine, you would see an ad for a topical treatment that said it would kill white line disease,” says Rob Spencer, farrier and co-owner of the Equine Podiatry Center located near Lexington, Ky. “You won’t find that anywhere now, and the reason is someone finally took the time to identify the (fungal) spores common in white line disease.”

Burney Chapman, a certified journeyman farrier and Susan Sharp, PhD, director