|White line disease (WLD) is a term used to
describe a keratolytic process on the solar surface of the
hoof, which is characterized by a separation of the inner zone
of the hoof wall (Redden, 1991). The separation occurs in the
non-pigmented horn at the junction between the stratum medium
and the stratum lamellatum. This separation is invaded by
opportunistic bacteria/fungi at the toe, quarter and/or heel
leading to infection, which progresses to varying heights and
configurations toward the coronet. The disease process occurs
secondary to a primary hoof problem such as chronic laminitis,
abnormal hoof conformation, hoof imbalance or any other
condition that causes a hoof wall separation. The disease has
been termed seedy toe, yeast infection, Candida and
Onychomycosis is a mycotic disease that originates in the nail
bed of the human and the dog. In WLD the infection originates
at the solar surface of the hoof and migrates proximally
approaching the coronary band but never invading it. In many
cases of WLD, the pathogens cultured are purely bacterial.
Until proven otherwise, onychomycosis may not be the
appropriate term when referring to white line disease in the
Anatomy of the hoof wall
The hoof wall consists of three layers; the stratum
tectorium (external layer), the stratum medium (the middle
layer), and the stratum lamellatum (the inner layer). The
stratum tectorium is the thin layer of keratinized cells that
give the wall its smooth shiny appearance. The stratum medium
forms the bulk of the wall and is the densest part of the hoof
wall. It consists of cornified epidermal cells arranged in
parallel horny tubules surrounded by intertubular horn which
grow distally from the coronary groove to the basal border. In
dark hooves it is pigmented except in the deepest layer. The
stratum lamellatum arises from the laminae, is nonpigmented,
and is responsible for attaching the hoof wall to the third
Distally at the sole wall junction, the dermal laminae end in
terminal papillae. These papillae are lined by stratum
germinativum which produces intertubular horn that fills the
spaces between the non pigmented horny laminae. This
association forms the bond between the hoof wall and the sole
known as the white line or zone (Figure 1A, 1B) 1.
When observed from the solar surface, this white line or white
zone is actually yellow in color and is a different
consistency than the dorsal hoof wall.
Figure 1A. Solar surface of hoof
Figure 1B. Lateral cut-away view of hoof-Stratum medium
extends from solar surface to coronary corium
Multiple causes of white line disease have been proposed,
but none have been proven. WLD can affect a horse of any age,
sex or breed. One or multiple hoofs may be involved. One or
multiple horses on the same farm may be affected. The problem
occurs through out the world.
Moisture may play a role as WLD is seen more in wet humid
areas but it is also seen in hot arid conditions. Excessive
moisture softens the foot, allowing easier entry of dirt and
debris into a separation leading to a secondary infection.
Continual bathing of show horses especially during the warmer
months may contribute to the incidence of WLD in this
population of horses. Excessive dry hoofs may form cracks in
the wall or fissures in the white line allowing pathogens to
invade. Poor hygiene is questionable since WLD often appears
in well-managed stables.
Infectious organisms, bacteria, fungi or a combination of
the two have been continually incriminated as a cause. What is
not known is whether these organisms are primary invaders or
secondary opportunists. Given the nature of these pathogens
usually isolated (mixed flora of bacteria, Pseudoallsheria and
Scopulariopsis fungi) they are most likely secondary
opportunists, which further damage an existing hoof wall
separation. The fact that WLD can be resolved with debridement
alone further detracts from this as a primary cause.
Figure 2A. Focal area of White line disease-So called "seedy
"Seedy toe" refers to a small circular separated area at
the sole/wall junction (Figure 2A). It is located on the solar
surface of the foot in the middle of the toe. This damaged
area lies directly dorsal to the notch on the third phalanx.
Figure 2B. Radiograph illustrates dorsal notch in the third
Excessive toe length or a clubfoot may compromise the blood
supply associated with this normal anatomical notch in the
third phalanx called the crena marginalis (Figure 2B). If the
circulation is continually affected, the commonly found "seedy
toe" lesion may progress to WLD.
Figure 3A. Lateral view of long toe-underrun heel. Note the
Mechanical factors that lead to a separation appear to be a
logical cause. These would include excessive toe length, poor
hoof conformation and various hoof imbalances such as long
toe-underrun heel or a clubfoot (Figure 3A). Damage to the
stratum medium/laminar junction will cause increased stress on
the remaining junction. Weight bearing and the force of the
deep digital flexor tendon will cause cycling to occur,
further weakening the bond 2. The more the
sole/wall junction becomes damaged; it removes all remaining
exterior protection allowing the separation to become more
Vascular damage to the hoof associated with chronic laminitis
results in a compromised laminar bond and a loss of integrity
(separation) at the sole/wall junction. Trauma from a
localized blow to the hoof causing vascular damage will also
lead to a focal hoof wall separation. WLD can be a sequel to
extensive sub solar or sub mural abscesses.
White Line Disease offers no threat to the soundness of an
animal until damage is sufficient to allow mechanical loss of
the attachment between the laminae and the inner hoof wall
resulting in displacement of the coffin bone in a distal
direction (rotation). Only then does the horse begin to show
discomfort. Most commonly, WLD is noted as an unexpected hoof
wall separation found by the farrier during routine hoof care.
In the early stages of White Line Disease, the only noticeable
change on the solar surface of the foot is a small powdery
area located anywhere along the hoof wall/sole junction. This
area may remain localized or it may progress to involve a
larger area of the hoof wall. Other early warning signs of
White Line Disease may be tender soles as seen with hoof
testers, occasional heat in the feet, and the sole will become
increasingly flat. A concavity ("dish") can be seen forming
along one side of the hoof and a bulge will present be on the
opposite side directly above the affected area at the coronary
band. There may be slow hoof wall growth, poor consistency of
hoof wall and a hollow sound will be noted when the outer hoof
wall is tapped with a hammer (Figure 3B) 3. Often
the disease goes undetected until the horse begins to show
Figure 3B. AP view showing concavity on medial side of foot
and bulge above defect on lateral side.
Lameness may or may not be observed. Hoof tester
examination does not always elicit a response The clinical
signs along with examination of the solar surface of the hoof
will confirm the diagnosis. On the solar surface of the hoof,
the sole/wall junction (white line) will be wider, softer and
have a chalky texture. Exploring the inner hoof wall which
lies dorsal to the white line will generally reveal a
separation filled with a white/grey powdery horn material.
Further exploration with a probe will give the depth and
extent of the cavitation. There may be a black serous drainage
from the separation.
If lameness is present a thorough lameness examination
should be performed including nerve blocks to confirm the
suspected area followed by radiographs. With extensive hoof
wall damage, WLD accompanied by pain can mimic laminitis both
clinically and radiographically.
Figure 4. Radiograph of Fig. 3A &3B showing severe rotation
Radiology can be very informative and should be considered
necessary. Good quality radiographs will show the extent of
the hoof wall separation and if rotation of the third phalanx
within the hoof capsule has occurred. They allow the clinician
to differentiate between white line disease and laminitis
(Figure 4). Radiographically, the separation in the lamina
will originate at the ground surface in white line disease
where as the separation will originate at the junction of the
inner hoof wall and the terminal laminar papillae in
laminitis. Pedal osteitis may be noted in the chronic case of
white line disease. Finally, radiographs can be used as a
guide when trimming and shoeing the horse.
Cultures are extremely difficult since the samples taken
from the separations are contaminated with dirt and
opportunistic organisms. Aerobic cultures usually reveal a
mixed bacteria flora while anaerobic cultures are negative.
Fungal cultures require a special media and time. The most
common fungal species cultured are Pseudoallsheria,
Scopulariopsis and Aspergillus. A biopsy taken at the juncture
between the normal and affected hoof wall shows a mixed
population of microorganisms. These will generally include
coccobacilli, yeast organisms and fungal spores. Inflammation
in the laminar dermis will be seen deep to the affected area
2. Laboratory findings have been unrewarding with
regards to treating this disease.
Correct the primary cause of the hoof wall separation (i.e.
excessive toe length, hoof imbalance, etc) if possible.
Therapy of White Line Disease is directed at treating the
affected area of the foot and supporting the foot with
therapeutic shoeing if hoof wall damage is extensive. Complete
hoof wall resection (removal of outer hoof wall to expose
diseased area) and debridement of all tracts and fissures in
the affected area is necessary. The veterinarian or farrier
should not reach blood during debridement. Thorough
exploration and debridement of any remaining tracts should
take place at 10-day intervals. When all tracts are removed, a
thorough examination is indicated at re-shoeing intervals
every 4 to 5 weeks.A wire brush is used daily to keep the
resected area clean.
Medical treatment follows hoof wall resection. Medical
treatment is of no value without resection of the affected
hoof wall. Disinfectants/astringents such as methiolate act as
a good disinfectant as well as a dye marker of the remaining
tracts. The dye marker will serve as an aid in making the
remaining tracts more visible at subsequent examinations. A
solution composed of equal parts gentian violet, acetone and
alcohol is also a suitable disinfectant and dye marker (Blue
Stuff R). Either preparation should be applied twice weekly as
not to make the hoof too hard. After thorough hoof wall
resection, the affected area can be left to grow out with
debridement at frequent intervals. Medical treatment may not
be necessary in many cases as debridement alone is sufficient.
The records from twenty cases of extensive white line disease
treated in this practice over a four- year period were
reviewed (O'Grady, SE. unpublished data). Fifteen of these
cases were treated with resection and continuous debridement
only. The remaining cases were treated with resection,
debridement and a dye marker. In all cases the resected
portion of the foot grew out and the hoof returned to normal.
Acrylic repair (medicated Equilox R) a should only be
considered after all tracts are resolved 4. It
should only be used in selected cases where the client is
unable to treat the resected area and where cosmetics are
important. The composite may hide and/or foster infection and
it tends to weaken surrounding normal hoof wall, which can
encourage re-infection. The antibiotic in the composite is
only effective against selected bacteria not fungi.
The type of shoe used depends on the extent of the damaged
hoof wall. If the defect is small, the hoof can be shod
accordingly. As the toe is involved in most cases of WLD, the
breakover is moved in a palmar/plantar direction as much as
possible. Fit the shoe so breakover is under the toe toward
the apex of the frog to remove the "lever arm" at the toe.
This will eliminate stress and pressure from the dorsal hoof
wall. It will also stop the "pinching" that often occurs at
the junction of normal hoof wall and the resection. If the
resection is extensive and/or if rotation of the third phalanx
is present, a support shoe (heart bar or egg bar-heart bar
combination) can be used. This type of shoe provides support
to the heel area of the foot and allows weight bearing to be
transferred from the affected part of the hoof wall
(toe/quarters) to the frog.
An alternative method would be to use a bar shoe or open shoe
combined with some type of impression material. The impression
material could be applied to the entire solar surface of the
foot as long as it was molded thicker at the heels to provide
the necessary support. It can be applied with or with out a
pad. If no rotation is present, a good "rule of thumb" is if
over half the dorsal hoof wall (distance from ground to
coronet) is resected, use palmar/ plantar support.
Figure 5A. White line disease with
Figure 5B Figure 5A with glue on shoe.
Note all pressure taken off sole in toe area
Glue on shoes utilizing the ground surface of the foot may be
the method of choice for shoeing the horse with WLD (figure
5A, 5B) 5. Hoof wall separations have historically
been treated by resection and acrylic repair so that nails can
be placed in the affected area to attach the shoe. However,
the disease process often will continue under the repair,
prolonging the time required for the hoof wall to grow out. By
gluing the shoes to the ground surface of the foot, the
resected area can be left open to be observed, debrided and
medicated regularly. Good palmar/plantar support can also be
provided with this procedure.
A change in environment is important. The feet should be kept
as dry as possible. Keeping the bedding clean and dry is
helpful. No turnout in rain or wet weather. Turnout can be
delayed in the morning until the sun can dry the pasture. A
well balanced diet with the addition of biotin and methionine
can be helpful (Hoof Rite R)b. The shoeing schedule should be
maintained at four week intervals.
Commitment from the owner with regards to a continuous
treatment schedule is necessary until all signs of disease
have been eliminated and then the foot/feet must be monitored
monthly until the hoof wall grows out. The extent of the
damage will determine the amount of time required for the
treatment process. For example, if the affected area extended
up near the coronary band in the toe area, it would take
approximately 10 months for the defect to fully grow out.
However, it is not always necessary for the horse to be out of
work for this entire period of time. The amount of exercise
permissible while treating WLD is dependent on the severity of
Prevention of WLD is difficult because the exact cause is
unknown. Discussing the problem with the farrier and having
him/her examine each foot when the horse is shod is extremely
important. Any small abnormal area involving the sole/wall
junction should be explored and treated. Proper trimming and
shoeing along with maintaining a short toe are essential for
creating a strong sole/ wall junction that offers protection.
Equally important is the necessity to carefully monitor hoses
that have previously had white line disease. A year or two
after WLD has been treated and resolved, it will suddenly
reappear in some horses with strong hoof walls that show no
sign of separation. WLD will often recycle time and again over
the horse's life (Jim Randell, 2000 personal communication).
Treating WLD has created a dilemma for owners, veterinarians
and farriers. Owners have been deluged with many different
causes and treatments. Many commercially available
preparations have been marketed for treating WLD, all claiming
success. Claims as to the efficacy of these products are
anadotal as there is no scientific evidence reported.
Veterinarians may be unaware of the magnitude of this problem
as they only see the severe cases that present with lameness
and radiographic changes. WLD may be a subtle contributor to
other causes of lameness within the foot. Farriers are very
aware of this disease as they are worried about nailing in
compromised hoof wall or lack there of and keeping the shoe on
between resets. They continually search for medical treatments
since owners are reluctant to have parts of their horse's hoof
wall removed at the farrier's recommendation.
An epidemiological study of the causes and relationships of
this disease would be valuable. Research, owner education and
continued farrier awareness appears to be the direction of the
1. Freeman LE, Dept of Anatomy, College of Veterinary
Medicine, Virginia polytechnic Institute, Blacksburg, VA
Personal Communication, 1993.
2. Turner TA, White line disease Equine Veterinary Education
2: 73-76, 1998.
3. O'Grady SE: White line disease. Journal of Equine
Veterinary Science 17(5); 236-237, 1997.
4. Turner TA, Anderson BH. Use of antibiotic-impregnated hoof
repair material for the treatment of hoof wall separation. A
promising new treatment. Proc 42nd Annu. Conv. Am Assoc Equine
Practnr. 205-207, 1996.
5. O'Grady SE, Watson E., How to glue on therapeutic shoes.
Proc. 45th Annu. Conv. Am. Assoc. Equine Practnr. 115-119,
a.) Equilox® - Equilox Int'l, 110 NE 2nd Street, Pine
Island, MN 55963
b.) Hoof Rite R---Professional Equine Products, P.O. Box 25,
Black Canyon City, AZ 95324
Dr. Steve O'Grady is veterinarian and farrier from the
Northern Virginia Equine Practice in The Plains, VA.