Page 94 - June 2018 Speedhorse

WHITE LINE DISEASE
by Heather Smith Thomas
The key to prevention is to keep the feet well balanced so there is a tight white line junction and no flares.
White line
disease is the
common term
for a progressive infection
and subsequent separa-
tion of the hoof wall, with
the wall coming loose
from the foot. This prob-
lem usually starts at the
bottom of the foot and
travels upward as this area
becomes hollowed out.
The hoof wall consists of
three layers, the stratum
externum, the stratum
medium and the stratum
internum. The visible
“white line” at the bottom of the foot between the hoof wall and the sole is not affected by this hoof infection.
Paul Goodness, Chief of Farrier Services at Virginia Tech’s Equine Medical Center in Leesburg, Virginia, says white line disease is an infection of the stratum internum and/or the junction between the stratum internum and the stratum medium of the hoof wall. This is the area just beneath the outer horny hoof wall between the hoof wall and the actual “white line” layer that is visible at the bottom of the foot. Pathogenic microbes that like to live in an airless environment can eat away at this part of the hoof just outside the white line.
The cause of this hoof deterioration is usually a com- bination of bacteria and fungi that are commonly found in the horse’s environment. “This is what we find when that disintegrating material inside the hoof is cultured,” Goodness says. “The infection usually, but not always, begins with separation in the hoof or intrusion into that area. The farrier usually discovers this disease by finding an odd opening into the foot.” Upon closer inspection, the opening may be very small compared to a larger hol- lowed out area up inside the hoof wall.
The infection may get started in a toe crack, quarter crack or in some old nail holes. Any hole
or break that goes through that area can allow microbes to enter. The severity of white line disease can range from small pockets in the white line
on the bottom of the foot, to large hollow areas
that extend all the way up to the coronary band. Sometimes you won’t see a cavity if the infection entered through a small pinpoint opening higher
in the wall. Then, there may be a hollow area in
the hoof wall, with little or no sign at the ground surface. Or, there may be a small tract at the ground surface and a huge cavity higher up inside the wall. You might hear a hollow sound when the hoof is tapped with a hoof pick or some other tool. One of the old terms for this condition was hollow hoof.
“This infection can affect any age, breed or gender—shod or unshod. It may affect only one hoof or multiple hoofs. It has been reported in almost any environment, from dry/arid to wet/humid.” People used to think it occurred mainly in wet, humid con- ditions, but it has been found in every environment. In the past, no one knew what caused it, and horse- men called the early stages seedy toe—due to the separation, debris and damaged material at the toe.
“This problem is usually discovered by a farrier when doing normal, routine hoof care, trimming
or shoeing, or by a veterinarian doing a lameness workup,” says Goodness. “It almost always is associ- ated with some type of poor hoof conformation, which can either be a cause or an affect. I rarely run across white line disease in a hoof that is perfect. There is usually some kind of imbalance that puts stress or strain on the foot, causing distortion, and it may be this poor conformation that causes the initial separation that allows an access for the microbes.”
White line disease has a characteristic appearance, with white, crumbly, chalky material in the affected area instead of healthy hoof tissue. White line disease by itself does not cause pain or lameness. If the hollow area in the wall becomes extensive enough, however, there will be some separation of the hoof wall that compromises support for the coffin bone.
“This generally results in some distal displacement
of that bone,” Goodness explains. “It tends to move or sink within the foot. The leg bones depend on support from the whole hoof to hold it up and if part of that hoof is compromised, something shifts and moves.” This can result in lameness and may hinder future soundness.
The foot loses some of the attachment that nor- mally binds the coffin bone to the hoof wall. It looks like laminitis, but is not. With laminitis, the laminae attaching the bone to the hoof wall fail and the bone drops. But with white line disease, the hoof wall attachment between the two epidermal layers fails. On radiographs, it looks like laminitis since the bone will move or displace, depending on where the wall damage is. The bone may rotate or it may sink to one side or the other at the quarter.
“As things start to shift, there may be some laminar sheering or solar compression by the bone, essentially bruising the sole from inside out. This can all happen very quickly,” Goodness says. Sometimes the coffin bone may drop so much that it detaches from the hoof wall and penetrates the sole. Thus, it is very important to catch it early.
“I recall an instance that occurred many years
ago before I knew about white line disease, when I noticed a slight separation in the toe of a broodmare,” Goodness says. “She was heavy with foal, which put even more weight on the feet. I was in a hurry, building
Paul Goodness, Chief of Farrier Services at Virginia Tech’s Equine Medical Center in Leesburg, Virginia,
Heather Smith Thomas
92 SPEEDHORSE, June 2018
equine health