Look up “white line disease” in your equine veterinary book, and you might not find it. This name for the condition was first coined in 1990, and the disorder is also known as seedy toe, hoof or stall rot, hollow foot, yeast infection, Candida, wall thrush, and (incorrectly) onychomycosis. But when white line disease came to be recognized as a unique condition what it’s called is of no consequence if a serious case of the disease puts your horse out of commission. In its worst stages, white line disease can leave a horse with little hoof wall and can cause permanent loss of athletic ability.

Opportunistic Invasion

Simply stated, white line disease refers to hoof wall separation within the hoof’s non-pigmented layer. Explains Tracy A. Turner, DVM, Dipl. ACVS, professor of Large Animal Surgery at the University of Minnesota, “White line disease is characterized by progressive hoof wall separation that occurs in the non-pigmented horn at the junction between the stratum medium (middle layer of the hoof capsule) and laminar horn. The separation is usually progressive and typically involves most of the toe and quarters. The name is a misnomer, as the white line is not actually involved, but rather the deepest layer of the non-pigmented stratum medium.”

The cause of white line disease is unknown, but it’s thought to be a multifactorial condition linked to an invasion into the area by infectious organisms such as bacteria and/or fungi. Stephen O’Grady, DVM, MRCVS, of Northern Virginia Equine in The Plains, Va., says these organisms might be secondary opportunists that invade the area after some sort of hoof wall trauma.

“One researcher hypothesizes that bleeding from laminar tearing—which can be caused by bruising, a long toe, etc.—may set up a very, very good medium for bacteria to grow in,” he says. “In other words, white line disease may occur from the inside and work i