White line disease (WLD) is a pathology that has long frustrated
farriers, veterinarians, owners, and other members of the equine
profession. WLD is described as a progressive hoof wall
separation originating at the solar surface of the hoof and
migrating proximally. It is thought to be the result of
opportunistic keratinopathogenic organisms invading the nonpigmented
stratum medium. The separation does not affect the
stratum internum or dermal tissues.
1 Historically, WLD has been
referred to by many other terms, including seedy toe, hollow
hoof, hoof rot, onychomycosis, etc. 1,2 Even though “white line
disease” has become the commonly utilized term for this
disease, it is a misnomer as the disease process does not actually
affect the white line of the horse’s hoof capsule. Therefore it is
this author’s opinion that the equine community should begin to
use the term “white zone disease” or another term that
describes the anatomy affected (non-pigmented stratum
medium/white zone).
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Fig. 1 - Cases of WLD are often first noticed by farriers
during routine trimming/shoeing visits. An area of
separation in the hoof wall that is filled with dirt/debris
is noted. |
The cause of WLD has long been debated. Although several
theories have been described, none have been proven. The
current theory of WLD etiology as described by O’Grady, Moyer
and others is that opportunistic, keratinopathogenic
microorganisms invade the non-pigmented stratum medium of
the hoof wall following an initial separation caused by a
mechanical stress or weakness, trauma, abnormal or excessive
moisture exposure, or some combination. 1,2 These organisms
degrade the keratin in the hoof wall exacerbating the separation. Furthermore, dirt and debris typically fill the separation,
acting as a mechanical wedge forcing the wall apart.
Although WLD has been reported all over
the world in many different environments,
the highest incidence of WLD appears to be
in areas with exposure to high
moisture/humidity. It affects horses of all
ages, breeds, sex, and type. Many factors
appear to predispose horses to WLD that
include but are not limited to: poor
environment, repetitive cycling of the hoof
from wet to dry conditions, various hoof
wall distortions, flexural limb deformities,
chronic laminitis and weak/brittle hoof
walls resulting from genetic or nutritional
abnormalities.
 |
Fig 2. - There can be rather large
areas of separation filled with
dirt/debris despite maintaining a
healthy appearance of the outer
hoof wall. |
| Fig. 3. - Lameness is usually only
noted when extensive separation
has occurred, resulting in an
instability of the distal phalanx
within the hoof capsule |
 |
Cases of WLD are often first noticed by
farriers during routine trimming/shoeing
visits. An area of separation in the hoof
wall that is filled with dirt/debris is noted (Fig 1). When removing the dirt/debris with a hoof knife or curette, an area of
undermined hoof of varying degree is revealed. After the dirt/debris is removed, portions of white/grey powder like hoof
wall are typically seen before reaching a healthy margin. There can be rather large areas of separation filled with
dirt/debris despite maintaining a healthy appearance of the outer hoof wall (Fig 2). Lameness is usually only noted when
extensive separation has occurred, resulting in an instability of the distal phalanx within the hoof capsule (Fig 3).
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Fig. 4 & 5 - The preferred packing of the
EPS at VMCVM is a mixture of oakum,
venice turpentinea and copper sulfate. |
Many cases of WLD are treated/managed by farriers during routine
visits. Farriers should be encouraged to debride small areas of
separation to a healthy margin whenever possible. If areas of
separation are to be covered by a horse shoe they should first be
packed with an antiseptic packing. The preferred
packing of the Equine Podiatry Service (EPS) at the
Virginia Maryland College of Veterinary Medicine
(VMCVM) is a mixture of oakum, venice turpentinea
and copper sulfate (Figs 4 & 5). For barefoot horses
with small separations, affected portions of hoof
wall should be removed to prevent mechanical
prying on the affected area as well as to prevent
further packing of dirt/debris while allowing the
owner to clean and treat the area (Fig 6).
 |
 |
| Fig. 7 - Carbide
cross cut burrsc |
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| Fig. 6 - Affected portions of hoof wall should
be removed to prevent mechanical prying on
the affected area. |
|
Areas of separation that are extensive, expand, or do
not resolve should be managed by a team consisting
of a veterinarian and a farrier. Radiographs,
specifically 0° lateromedial and 0° dorsopalmar,
should be used to identify the extent of the
separation and to guide trimming/shoeing. The
principles of treatment are to resect the affected
hoof wall and debride to as healthy of a margin as
possible (exposes the area to UV light and air),
stabilize the hoof capsule, recruit the sole and frog
for load sharing, and remove predisposing factors
(environment, excess leverage, etc.).
To resect the hoof wall a combination of half round
nippers, hoof knives, loop knives, and motorized
rotary tools (Dremel
b
) are used. Carbide cross cut
burrsc are useful to prevent dust and heat buildup (Fig 7). Following resection many topical products can be applied to
further disinfect and dry the hoof. The preferred topical treatment at the VMCVM is 2% tincture of iodine. It is important
to note that all topical treatments are of little to no value when there is insufficient debridement. Figures 8, 9, & 10 show a
sequence of debridement prior to topical treatment. If there is enough healthy hoof wall remaining a shoe
should be applied.
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Fig. 8, 9, 10 - A sequence of debridement prior to topical treatment |
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Fig. 11 - It is important to note that affected areas should
not be covered with adhesive. |
For areas of small resections a normal shoe can be applied.
For larger more extensive resections, utilizing a shoe/setup
to spread load away from the wall onto the sole and frog
and to support the distal phalanx within the hoof capsule
should be used. Such shoe/setups include but are not
limited to heart bars, heel plates with impression material,
Equi-Pakd
, and frog pads. When there is not enough hoof
wall to safely and securely attach a shoe with nails, a glue
on shoe can be applied. It is important to note that
affected areas should not be covered with adhesive (Fig 11).
Ultimately, if there is not enough healthy wall to attach a
shoe the foot should be bandaged or placed into boots
until there is sufficient wall to nail or glue to
In conclusion, horses being treated for WLD should be kept
in a clean and dry environment with minimal variations in
moisture level. The hooves should be cleaned out and
treated at least once daily. They should be rechecked by the
vet/farrier team at 4 week intervals for continued
debridement and to monitor the hooves for appropriate
growth.
