Contrary to what it's name implies, white line disease is not truly a "disease" and it does not actually affect the "true white line" according to The Horse.com
. White line disease is more accurately described as a bacterial or fungal infection in the nonsensitive layer go the outer hoof wall that progresses to the layers of the hoof. The infection slowly moves up the "nonpigmented" space in the stratum medium layer of the hoof. The tissue affected by the infection turns to a chalky powder and eventually separates the the laminae and coffin bone allowing for the rotation of the coffin bone.
The infection that causes white line disease in the horse starts very small in a damaged area of the hoof between the sole and the wall. It can also start in the small spaces created in the hoof where tearing and weakening occur due to the "failure of the white line." According to one farrier
, it is more commonly contracted in hotter, more humid areas as well.
Many times, white line disease can be detected by a farrier in a normal appointment when the shoe is removed. The initial sign is a "dark crumbly spot in the white line area" this is referred to as a "seedy spot." At this point, the horse feels little to no pain. If the infected area of the hoof is not trimmed away, the infection will continue to grow due to the presence of anaerobic bacteria that thrive on the lack of oxygen. Other signs of white line include a "soft, cheesy hoof horn" and a bulging appearance of the hoof wall. Lameness does not occur right away with this condition, in fact, horses may not exhibit lameness until the condition become serious.
A hoof showing the bulging symptoms of white line disease.
If white line disease is not taken care of immediately it can become far more serious. The entire infected part of the hoof needs to be removed and completely exposed to oxygen. In these cases of white line, a farrier will be able to "hear the hollowness" in the hoof as the tissue behind the hoof wall becomes more and more infected. First, the farrier removes the the infected part of the outer hoof capsule, after this the remaining dead tissues are removed as well as the previously mentioned chalky powder created from the deterioration of the hoof. The process of removing all the infected tissue on a horse's hoof is called resection. After resection, the horse's hoof is shod with a "bar shoe." This bar shoe is put on the help handle the weight of the horse after the hoof wall has been removed. Glue is preferred over typical nails to attach the shoe.
Oxygen must continue to get to the area that was infected by whittling to assure that the infection does not come back and the hoof is able to heal.
An infected hoof after a resection procedure.
White line can be prevented in most cases. Simple precautions such as regular, proper hoof trimming and care; and, keeping areas where horses are clean and free of areas where fungus and bacteria can grow. Additionally, the regular inspection and cleaning of hooves help to maintain overall hoof health.
This picture shows the "soft, cheesy" appearance of an affected hoof.