Hoof Disease threat Grows
Stephen E. O'Grady, D.V.M.
Farriers and veterinarians are noticing a growing problem in
horses' hooves called White Line Disease. It appears to be more
prevalent in hot, humid areas but has been occurring in all parts
of the United States with increasing frequency. It doesn't seem
to be an issue of poor hygiene, as the problem is seen in
well-managed stables. Yet it's difficult to prevent because
veterinarians and farriers are unsure of its cause.
Just what is White Line Disease? Simply put, it is deterioration
of the inner part of the hoof wall. The "white line" refers to
the distinct non-pigmented inner layer of the hoof wall. On the
ground surface of the foot, it lies next to where the hoof wall
joins the sole.
In the disease's early stages, the only noticeable change on the
ground surface of the foot is a small powdery area located along
the hoof wall/sole junction. This may remain localized, or it may
progress to a larger area of the hoof wall.
White Line Disease may be found in one foot or all four and is
found among all breeds of horses. It begins with a separation
between the hoof wall and the sole. This can occur in several
places-the toe area, the toe and quarter of the foot, or the
heel. This separation removes the protective part of the hoof
wall/sole junction and allows bacteria and fungi-pathogens
readily found in the environment-to enter. These organisms may
also gain entry through cracks in the feet, nail holes or
fissures at the white line.
The destructive effects of these pathogens lead to progressive
deterioration of the inner hoof wall.
The term is also used to describe seedy toe in its early stages-a
small, circular powdery area in the hoof wall at the center of
the toe in many horses.
Factors contributing to separation at the hoof wall/sole junction
are excessive moisture; unbalanced feet; improper trimming, an
acute hoof angle such as that seen with long toe-underrun
conformation; flexure deformities (contracted tendons); clubfoot
and concurrent hoof problems such as hoof cracks; chronic
infection (abscesses or gravel); or direct trauma with subsequent
bleeding.
White Line Disease can also occur secondarily to chronic
laminitis where the laminae and associated hoof wall are
compromised.
White Line Disease poses no threat to the animal's soundness
until extensive damage is done. The horse will only appear lame
after the disease has caused the laminae and the hoof wall to
separate, resulting in the rotation of the coffin bone.
Early warning signs of the disease may be tender soles as seen
with hoof testers; occasional heat; the sole becoming flat; a
dish forming along one side of the hoof, with a bulge on the
opposite side directly above the affected area; slow hoof wall
growth; poor consistency of hoof wall; and a hollow sound when
the outer hoof wall is tapped with a hammer. On the ground
surface of the foot, the white line becomes wider and softer and
has a chalky texture.
In the early stages, keen observation by your farrier is
necessary to detect subtle changes in the ground surface of the
foot. More often, the disease goes undetected until the horse
begins to show discomfort. At this point, the affected area can
be readily found on examination of the foot, and the extent of
the hoof wall loss can be determined with X-rays. With extensive
hoof wall damage, the painful stage can mimic laminitis both
clinically and in x-rays.
Treatment of White Line Disease is directed at the affected area
of the foot and supporting the foot with therapeutic shoeing if
hoof wall damage is extensive. Regardless of the extent of
damage, the affected area must be treated through
resection-removal of the outer hoof wall to expose the diseased
area-and debridement-removal of damaged tissue.
The exposed area is debrided every two weeks until there is a
solid junction between the inner hoof wall and the lamina. At
this point, the area can be left to grow out with periodic
debridement, or the defect can be repaired with an acrylic
substance.
Alternatively, various medications such as merthiolate, betadine
ointment or two percent iodine can be applied to the debrided
area. All of these preparations are used to treat infections and
have a drying effect. These medications are applied to the
affected area, and the area is packed with gauze and held in
place with duct tape.
Another method is to use a piece of sheet metal cut and molded to
fit over the defect on the outer hoof wall and attached with
screws. This keeps the area clean and allows the packing to be
changed at regular intervals. Whatever the treatment, it must be
combined with thorough debridement.
The type of shoe needed depends on the extent of the damaged hoof
wall. If the defect is small, the hoof is balanced and the foot
shod normally. If the resection is extensive, a full-support shoe
(heart bar or egg bar-heart bar combination) is used. The shoe
must allow any diseased area of the hoof wall from the toe to the
heels to be resected and treated while providing adequate
support. The full-support shoe supports the heel and allows some
weight-bearing to be transferred from the hoof wall to the frog.
The extent of the damage determines the amount of time required
to treat the disease, as the affected area has to grow out. For
example, if the affected area extended up near the coronary band
in the toe area, it will take about 10 months for the defect to
fully grow out. However, it is not usually necessary for the
horse to be out of work this entire time. The amount of exercise
permissible while treating White Line Disease depends on the
severity of the damage.
Discussing the problem with your farrier and having him examine
each foot when the horse is shod is extremely important. Any
small abnormal area should be explored and treated. Proper
trimming, balancing of the foot and correct shoeing are also
vital to maintaining a healthy foot.
Stephen E. O'Grady, D.V.M., operates Northern Virginia Equine
Podiatry Center near Marshall, Va.
