“A great number of bacteria and fungi have been incriminated in the

ADVANCED LESIONS.The integrity and weightbearing capability of a hoof can be destroyed
by advanced lesions caused by fungi.
“A great number of bacteria and
fungi have been incriminated
in the pathophysiology, but
sample collection techniques
used in previous studies have
been open to criticism...”
Editor’s Note: This article by Michael Wildenstein recounts a recent study he
conducted to isolate the cause of hoof wall separation attributable to white
line disease and to thereby validate a treatment approach. Wildenstein is the
resident farrier in the College of Veterinary Medicine at Cornell University
in Ithaca, New York. He is a certified journeyman farrier and a fellow of the
Worshipful Company of Farriers of Great Britian.
By Michael Wildenstein CJ, FWCF
WE CAN NOW SAY with confidence that we have a safe and effective treatment method for white line disease, which is a fungal infection of a horse’s
hoof. More specifically, my study eliminated any doubts that hoof wall separations attributable to white line disease are caused by fungi that can be
treated with a chlorine dioxide solution.
Fungi have long been thought to be a cause of white line disease, but bacteria
or yeast have also been blamed. Previous studies did not pinpoint the infectious
agent with certainty,leaving the most effective treatment method also open to question. The doubts surrounding the disease are mirrored in the many names by which
it has been known through the years.
December, 2003
SOLAR VIEW. Lesions of the stratum medium as
seen from the solar surface of the hoof. In such
cases a fungal infection creating a cavity may
be secondary to an injury, abscess or laminitis.
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“We hypothesize that mechanical stress created by excessive toe length, laminitis, poor
management or injury predispose horses to the collection of environmental contaminants
within the stratum medium. All of the identified fungi can be cultured from soil and wood...”
Historical Perspective
The term “white line disease” has been
given to the progressive separation of the
hoof wall of the horse. The term is used
prominently today, though it is used interchangeably with “onychomycosis” to
describe the cavities formed in the hoof
wall by fungal activity. Onychomycosis
is derived from Latin. Onych means claw
or nail, mycosis means infection or
disease caused by a fungus.
In 1864,Antonio Pires described hoof
wall separation and its treatment. His
anatomical description of the wall separations were accurate and define the
condition in the horse’s hoof that we call
white line disease.
In 1884, A. Lungwitz descri b e d
“hollow wall” as a separation between
the middle layer of the wall and the keraphyllous layer. Lungwitz said the condition was rare and that the cavity was
usually filled with crumpling, disintegrated horn.
In 1897, A . W. Dollar, M R C V S,
described the condition as “loose wall,”
a rare condition. Dollar said the condition
was due to a fungus-like organism that
entered the inner sheath of the wall and
induced change in the horn. In 1903, Prof.
William Russell referred to the condition
as “foot rot” or “seedy toe,” which manifests itself in the wasting away or drying
up of the sensitive laminae.
Sketches by Russell and Pires accurat e ly depict lesions in the strat u m
medium as we see them today. The
lesions start at the toe quarters and spread
in a proximal palmar direction and affect
the innermost stratum medium.
Modern Descriptions
Tracy A. Turner, DVM, MS, Dipl.
ACVS, found the condition referred to as
a yeast infection, candida and hoof rot.
Rob Sigafoos, farrier at the University of
Pennsylvania veterinary school, referred to
the condition as “subdural erosive lesion.”
In 1995, Doug Butler PhD, CJF,
FWCF, described a progressive pododermatitis that appeared like a granulated
cheese mixture, which was the digested
stratum medium left behind from the
fungi. When the residue was cultured, a
smorgasboard of fungi was found.
Hoof wall separation is mentioned
frequently in modern farrier literature.
Hickman’s Farriery, 1997, described
“seedy toe” as a cavity between the horny
and sensitive laminae filled with a mealy
type of horn. This description fits the
criteria for onychomycosis because of
the cavity described.
Dr. Ric Redden is said to have coined
the term “white line disease” to describe
a separation of hoof wall that is distinct
f rom laminitis. Fa rrier Burn ey
C h ap m a n , who spent more time
studying the condition than anyone else,
referred to it as onychomycosis, which
is well known in human medicine and
refers to a fungal infection affecting the
toenails or fingernails. It may involve
any component of the nail unit including
the nail matrix. Sometimes trauma or
damage to a nail predisposes the development of the condition.
The term onychomycosis is appropriate for horses when the disease is a
fungal infection of the hoof wall,usually
secondary to mechanical stresses related
to injury, poor management or other
disease processes.
Foot Structure and Terms
The wall of the hoof grows from the
epithelium covering the coronary dermis.
It consists of horn tubules that are
embedded in the intertubular horn, which
is attached to the coffin bone and hoof
PREVENTING WHITE LINE DISEASE
Careful management of equine stables and the picking of the
hooves on a daily basis will reduce the incidence of fungal
infections of the hoof responsible for white line disease.
In humans, toenail fungus commonly affects the traumatically stressed toes of runners, and the treatment is
focused on the fungal infection rather than the mechanical
stresses produced by running. Because a horse depends on
the integrity of the hoof wall to stand or move, the focus here
is prevention.
All of the horses with a severe fungal infection in the study
detailed in the accompanying article had previous damage
to the hoof. The damage was created by laminitis, an
abscess, hoof wall avulsions or cracks, and horseshoe nails.
Hot seating horseshoes in the application process will
eliminate the fungi between hoof and shoe, thus decreasing
the risk of transporting fungal spores into the hoof wall with
the horseshoe nail.
46
The application of shoes on hooves with avulsions or
cracks will help protect the affected area by preventing a
buildup of debris.
Reducing the use of hoof pours or urethane packing
(which create an environment condusive to fungal growth)
will reduce fungal activity. Properly placed shoes will protect
the hooves from the breaks and splits that provide access for
fungal spores.
Soaking laminitic or abscessed feet with chlorine dioxide
will prevent serious fungal infections. The use of iodine on
the sole will reduce fungal populations. Fungi can consume
the insensitive sole, leaving little or no natural protection.
Using a hoof antiseptic with povidine iodine will likewise
protect the hoof from serious fungal lesions. Activity and
movement of the horse improves circulation and the body’s
defense against fungal and bacterial infections.
—Michael Wildenstein
AMERICAN FARRIERS JOURNAL www.americanfarriers.com
December, 2003
TREATING WHITE LINE DISEASE
By Michael Wildenstein
The most effective treatment of white line disease
(onychomycosis) requires removal of the affected tissue and
sterilization of underlying tissue, followed by antifungal
treatments.
The use of antifungals alone produces negative results
until the overlying hoof wall is removed. The removal of
portions of the hoof wall allows the antifungals to be applied
directly to the fungal infection. Antifungal drugs such as
miconazole, clotrimazole and itraconazole are of benefit.
Exposing The Lesion
The most important aspect of treatment is carefully
removing all affected tissue and cleaning the area. It is
important that the wall is not pulled or pried off as this could
damage the laminae. Removal of the hoof wall over the
lesion is safely done with a half round nipper, a rasp and a
bone curet. The curet is helpful when opening the smaller
regions of the lesion. The lesion is identified by the chalky
subungual material.
The area is then cleaned by soaking the affected hoof in
a solution of chlorine dioxide at 20,000 parts per million. It
is important to soak the hoof using a bag or innertube to
prevent the gas from the solution from escaping. The gas is
effective in reaching the fungal spores on the hoof.
Chlorine dioxide is safe at 20,000 ppm and does not affect
the hoof in a negative way. Hoof ailments such as thrush and
canker have fungal and bacterial agents that are also eliminated with chlorine dioxide. Dentists use it to treat bacterial, fungal and yeast infections of the mouth, and it is also
cartilages. The three basic layers of the
wall structure consist of the stratum
externum, medium and internum.
The stratum externum consists of
horn tissue produced by the perioplic
dermis, which lies directly proximal to
the coro n a ry dermis. The strat u m
externum is only a few millimeters thick
and is somewhat rubbery near the coronary band and is dehydrated over the
distal hoof wall. The bulk of the hoof
wall is made up of the pigmented horn
tubules of the stratum medium. The
nonpigmented stratum internum consists
of approximately 600 laminae that interdigitate with the sensitive laminae of the
laminar dermis.
The dermis of the sole is fi rm ly
attached to the undersurface of the coffin
bone and produces a mixture of horn
tubules and intertubular horn. The junction between the sole and the wall is the
white line (zona alba). The white line
includes some of the non-pigmented
December, 2003
used in the food industry for cleaning vegetables and by food
processing plants.
Soaking The Hoof
Soaking the hooves is done on a weekly basis until the
lesion is grown out. It is also important to check the hoof for
active lesions on a weekly basis to avoid progression of lesions
not found during the initial debridement.
Covering the affected area with a hoof patch is contraindicated because fungal spores can be trapped, producing
another lesion.
The lesion is covered with felt to protect the hoof and
allow for the introduction of antifungals.
The application of a hoof cast to protect the hoof when a
significant portion of the hoof has been removed will be
beneficial. The hoof cast is temporary and should be checked
on a daily basis for irritation to the heel bulbs. The cast will need
to be removed within 21 days. The application of a cast
requires the horse to be stalled in a clean and dry environment.
Shoeing May Help
A shoe can be applied to the cast to prevent wear and
further protect the hoof. A treatment boot or hoof boot may
be of temporary help during the treatment period.
If enough hoof wall exists to allow for nailing a support
shoe to the hoof, it will provide more permanent protection
than a cast or hoof boot. Nail holes can be punched in the
shoe to allow for nailing to healthy wall. Clips on the horseshoe will stabilize the shoe and prevent stress on the existing
hoof wall. The application of a shoe will ease the soaking and
medicating process.
stratum medium of the wall, the distal
ends of the horny laminae and the
pigmented horn produced over the
terminal papilliae of the laminal dermis.
The condition is restricted to the
inner-most area of the stratum medium.
This area has a moisture content of 75
percent in a normal hoof. The first indication would be a separation between
sole and wall as viewed from the solar
surface. Material removed from the separation with a thin probe will yield dirt,
manure, digested horn and residue that
resembles dry cheese.
The separation may advance to the
coronary corium. The extent of the separation can be seen by taking radiographs.
By gently tapping on the hoof wall the
affected area will sound hollow. In a
chronic case, a bulge will be present in
the hoof wall at the most proximal point
of the infection. As with all fungal infections of the hoof wall, a distinct odor
will be present.
The Controversy
White line disease has been a debated
issue for years and has been a source of
contention among farriers and veterinarians. A great number of bacteria and
fungi have been incriminated in the
pathophysiology, but sample collection
techniques used in previous studies have
been either unreported or open to criticism for possibly allowing contamination of the samples.
There is one report in the veterinary
literature (Pathomorphological Findings
in a Case of Ony ch o mycosis of a
Racehorse, by Kuwano, et al, from the
Japan Racing Association, Journal of
Veterinary Medical Science 58 (110:
1117-1120, 1996)) that demonstrates,
with histopathology, that disease of the
white-line area is caused by a fungus.
In the 1990s, Burney Chapman urged
horseshoers to send samples from lesions
in horses hooves to Mt. Sinai Medical
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47
AVOIDING CONTAMINATION. Here the hoof is sterilized and
an iodine-impregnated surgical sticky drape is applied.
Center to be analyzed by Susan Sharp,
Ph.D. She cultured 156 separate fungi
from 100 samples. Chapman defined the
disease as a fungal infection of the hoof
wall secondary to mechanical stresses
related to poor management or other
disease processes.
Lay equine literature and farrier trade
journals contain many anecdotal reports
and uncontrolled mini-studies postulating
a great number of causes and predisposing factors of hoof wall separation.
In 2000, a study done by M. Keller, S.
Krehon, C. Stanek and R. Rosengarten
found 26 species of molds and five
species of dermatophytes on 187 hooves.
This study as well as others show a great
variety of fungi on the horses hooves.
But the questions remained: Is the
disease a primary or secondary infection
caused by bacteria, by fungi, or both? If
it is secondary, what are the predisposing factors?
Study Overview
Poor hoof quality can result from
genetics, environment, management,
nutrition and infectious agents. The goal
of this study was to define one type of
fungal lesion and to secure samples taken
in a way that the primary fungi could be
collected while ruling out yeast and
bacterial factors.
In an effort to isolate the causative
factor in hoof wall lesions, one type of
lesion, hoof wall separation, was studied.
The type of hoof wall lesions looked at
48
COMPLETE REMOVAL.The dorsal hoof wall over the lesion
was completely removed in this case to provide access to
and elimination of the cavity-causing fungi.
in this report were cavities created by
fungi in the innermost stratum medium
of the hoof wall. These lesions can create
large voids that can separate the wall
from the laminae that connects the hoof
wall to the third phalanx. This type of
lesion can have devastating effects on
the integrity of the hoof wall.
In an effort to identify the infectious
agents, I took samples from poor quality
hooves and had them examined for the
presence of fungi and bacteria.
Case Selection
All horses presented to the farrier
service were evaluated for the clinical
signs of “white line disease.” The hooves
identified as having a visible separation
of hoof wall with a dry/chalky texture or
those with bulges and abnormal percussion were selected for the study.
A total of five infected hooves were
evaluated, with the average age of 5 years
old. The hooves were of four geldings
and one mare. These horses had visible
separation of hoof wall with a dry/chalky
texture or wall bulges and abnormal
percussion.
Four horses determined to have no
hoof irreg u l a rities or lesions we re
selected for the control group.
Careful Sample Collection
On the diseased hooves, the leading
edge of the lesion was found by using
hoof wall percussion and radiographs.
In all suspected cases, there was a distinct
hollow sound to percussion that disappeared half the distance or greater from
the sole to the coronary band.
A marker was placed at the point that
the percussion changed, and radiographs
were used to verify the edge of the lesion.
Samples were taken at that point.
An attempt was made to sterilize the
hoof wall prior to sample collection. The
hoof wall was painted with concentrated
fo rm a l d e hyde three times, with 5
minutes between applications.
At that time, a 1-centimeter diameter
portion of the stratum externum was
removed with a sterilized dremel bit and
the fo rm a l d e hyde ap p l i c ation wa s
rep e ated with a final swabbing of
concentrated iodine placed on the created
wall defect.
The hoof wall and pastern were then
covered with an iodine impregnated
surgical sticky drape and a small window
was cut out over the created wall defect;
sterile surgical gloves were worn. Sterile
bone curettes were used to remove the
stratum medium.
Approximately 70 percent of the
stratum medium was removed, revealing
the edge of the lesion. The stratum
medium removed for culture was dry
and chalky and not of normal texture or
integrity. The material was transferred
into a sterile container for culture.
All samples we re asep t i c a l ly
submitted to the New Yo rk Stat e
Diagnostic Laboratory for aerobic/anaerobic bacterial and fungal culture.
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December, 2003
Fungi Found
Closing Statement
The four control hooves did not grow
any bacteria or fungi, whereas the five
diseased hooves grew four types of fungi.
The same species of fungi were found in
samples taken from soil. The hooves with
lesions did not grow any bacteria.
Foot Bacterial
Fungal
No.
Culture
Culture
The goal of this study was to find a
valid method to aseptically collect and
culture material from cases of hoof wall
separation. The results support a primary
onychomycosis as the causative factor in
hoof wall separation.
Once it was determined that fungi was
the sole infective factor involved, I
looked to find a potent yet safe antifungal
for use in the treatment. A solution of
chlorine dioxide at 20,000 parts per
million proved to be an excellent choice.
This potent disinfectant used on a
properly prepared hoof eliminated the
presence of fungal spores. I have had
positive results using this chemical on
thrush, canker, scratches and rainrot.
Chlorine dioxide at 20,000 ppm is activated using 1 deciliter chlorine dioxide,
1 deciliter of vinegar with 4 liters of water
for a safe effective method of treating
fungal infections of the horse’s hoof.
This study does not include a large
number of cases, but the results were
very consistent. It is my hope to continue
building on this foundation by culturing
more cases. The most exciting part about
this study was finding a safe and effective treatment method for fungal infections of the horses hoof.
1.
2.
3.
No growth
No growth
No growth
4.
5.
No growth
No growth
Trichoderma sp
Mucor sp
Aspergillus
glaucus
Gliocladium sp
Gliocladium sp
Preliminary Conclusion
The fact that all of the controls were
negative for both bacterial and fungal
growth validates the sample acquisition
as a methodology for collection of sterile
samples of the stratum medium for
culture. The absence of bacteria and positive growth of fungi supports the role of
a fungal infection and, t h e re fo re,
supports the term “onychomycosis” in
describing this disease.
All four species of fungi cultured are
known to be keratinophilic. This does
not mean that they have the ability to
cause primary keratin disease, but they
have the ability to grow well on keratin.
Trichoderma readily degrades cellulose and will grow on other fungi. Mucor
is found in horse dung, leather products,
animal hair and jute. Aspergillus glaucus
is a common outdoor fungus in the
winter and can be found growing on
leather, grain and wool. Gliocladium is
structurally similar to penicillin.
We hy p o t h e s i ze that mech a n i c a l
stress created by excessive toe length,
laminitis, poor management or injury
predispose horses to the collection of
environmental contaminants within the
stratum medium. All of the identified
fungi are environmental organisms and
can be cultured from soil and wood.
The inner environment of the stratum
medium (chemical composition, oxygen
tension and the limited availability of
microbial substrates) selects for species
of fungi that can survive and grow well
on keratin.
December, 2003
r
TRAPPING GASES. The use of an IV
bag or an inner tube to while soaking
the hoof in a chlorine dioxide solution allows gases from the solution to
attack fungal sprores.
HOOF CAST. If a shoe cannot be used to protect the hoof during treatment, a hoof
cast can be another option.
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