Equine canker is a disease in search
of a definition since the cause
has not been determined. It could
be described as a pathological response
to an insult to the foot’s horn-producing tissues. Equine canker has been
defined as an infectious process that
results in the development of a chronic,
hypertrophic, moist pododermatitis of the hornproducing tissues, generally in the palmar
/ plantar sections of the foot. Usually originating in the frog, canker may remain focal
or invade the adjacent sole, bars and hoof
wall. Canker is generally confined to and
proliferates from the epidermal tissue and
rarely invades the underlying dermal tissue.
Although the etiology of canker remains
elusive, it can consistently and effectively
be treated and resolved.1,2,3,4
Etiology Of Canker
The etiology of canker remains evasive, but generally is seen in a frog that is
unhealthy and enters through a break in the
horn tissue. There is another disease entity
termed “coronary band dystrophy,” which
appears to have an immune-mediated component that is associated with or can lead
to canker (O’Grady SE. “Coronary Band
Dystrophy,” 2017, in review). Wet environmental factors may play a role as there
is a seasonal incidence of canker during
the rainy season in Florida from July until
Previously, it was felt that unhygienic
conditions were causative, but canker
is seen in horses that are well cared for
and receive regular hoof care. At one
time, canker was commonly seen in draft
breeds, but now is diagnosed in all breeds,
especially Thoroughbred and warmblood
horses. It can occur in one or multiple feet,
affect one or multiple horses on a given
farm and has no predilection to the age or
sex of the horse.
Figure 1: A foot with chronic thrush.
Note the unhealthy nature of the frog
and the loss of structural mass.
Figure 2: Early canker in the center of
the frog. Note the light brown epithelial tissue that is trying to surround
the ulcerated lesion.
Clinical Signs Of Canker
Canker generally originates in the frog
and can be mistaken for thrush in the early
stages. Thrush is limited to the frog and
results in a very recognizable deterioration
or loss of frog tissue where on the other
hand there is a proliferation of tissue with
canker (Figure 1).
Canker may present anywhere from a
focal area of granulation tissue in the frog
that bleeds easily when abraded to long
filamentous fronds of hypertrophic horn.
Canker is characterized by numerous small
finger-like papillae consisting of a soft,
off-white material that resembles a “cauliflower-like’ appearance and is covered
with a caseous white exudate that resembles cottage cheese (Figures 2 and 3a-3c).
Figures 3A, 3B & 3C: Figure 3A (left) shows filamentous fronds of hypertrophic horn. Figure 3B (center) shows
the finger like papillae that presents a “cauliflower” appearance. Figure 3C (right) shows a white caseous exudate
that resembles “cottage cheese” beneath the outer hard layer of the frog. The condition is frequently, but not
always, accompanied by a foul odor.
The condition is frequently, but not
always, accompanied by a foul odor.
However, if any type of antiseptic or caustic
medication has been used for treatment, the
smell will disappear. The affected tissue
will bleed easily when abraded and may
be extremely painful to the horse when
touched or pressure is applied. Varying
degrees of lameness will be present
depending on the extent and depth of the
infection. Most horses are not lame if the
disease is recognized and treated early.
Figure 4: Photomicrograph on the left shows normal epidermis/dermis of
frog. Photomicrograph on the right shows the tissue affected with canker.
Red arrow is papillary hyperplasia, green arrow is keratolysis, yellow arrow
is degeneration of the outer layer of the epidermis and blue arrow is a mixed
population of bacterial organisms.
Diagnosis Of Canker
A presumptive diagnosis of canker is
based on ruling out the presence of thrush,
the gross appearance of the affected horny
tissue covering the frog, a fetid odor and
the ease with which the abraded tissue
bleeds. However, a definitive diagnosis
may be confirmed with a biopsy. Biopsy
is most useful in recurrent cases or when
the lesions do not have the characteristic
appearance or location in the foot.
Histologically, the lesion is read as a
“chronic hypertrophic moist pododermatitis.” It is characterized by a proliferative
papillary hyperplasia of the epidermis
with dyskeratosis, keratolysis and ballooning degeneration of the outer layers
of the epidermis. A mixed population
of bacterial organisms are observed in
the stratum germinativum layer of the
epidermis of the frog (Figure 4). Cultures
per se are unrewarding as they typically
produce an assortment of environmental
organisms such as “Bacteroides sp.” and
“Fusobacterium necrophorum,” the usual
opportunistic bacteria found in the solar
surface of the horse’s foot.
Figure 5: No canker present in the
frog, but note how the foot should be
prepared prior to debridement. Note
the slope of the bars for exposure of
Treatment Of Canker
Treatment of canker is a realistic
example of a joint venture between a veterinarian and a farrier. From a legal and
ethical standpoint, working with dermal
tissue is the practice of veterinary medicine. The effective veterinary treatment of
canker requires sedation, local anesthesia,
surgery (debridement without hemorrhage)
and medication. Many veterinarians are
not familiar with farrier tools or their use,
unable to trim and prepare the foot prior
to debridement, are unable to explore the
hoof capsule appropriately and are unable
to provide the necessary follow-up farriery
care. This describes the farrier’s role and
input. Treatment should be considered a
team approach with the veterinarian, farrier and owner/caregiver
Trimming and preparation of foot. An
important aspect that is often overlooked
is to trim the foot prior to surgery. Try to
address any hoof capsule distortion at the
onset in order to give the foot a mechanical advantage. All loose exfoliating sole
is removed from the solar surface of the
foot. The bars and sole of the hoof capsule
adjacent to the frog are explored to be sure
the horn in this area is not involved. All
underrun or loose horn is removed down
to solid structures (Figure 5).
Figure 6: Esmark bandage in place.
The heels are trimmed such that the hoof
wall at the heels and the frog are on the
same plane or approach the same plane.
The frog should not be recessed between
the heels of the hoof wall at the beginning
of treatment or the affected tissue will not
heal. I also trim the bars on more of a slope
than usual because I want good exposure
to the sulci around the frog. After the foot
is prepared with the appropriate farriery,
soaking the foot with any of the various
cleaning solutions or products is unnecessary. The foot is now placed in a bucket
of clean water and the foot is scrubbed
thoroughly with an antiseptic soap using a
firm brush. I prefer to do the debridement
standing under local anesthesia but it can
be done under general anesthesia if there
are behavior issues with the horse or at the
discretion of the clinician.
Debridement. A tourniquet such as an
Esmark bandage or a length of tire inner
tube cut at a 3-inch width is placed starting
at mid-pastern to above the fetlock (Figure
6). It is essential to create a bloodless field
so the demarcation between normal and
diseased tissue can be seen during debridement. All abnormal tissue is removed until
the tissue resembles a pink velvet color with
numerous pin-point hemorrhages, which
are the dermal papilla (Figure 7).
Remember that canker is generally limited to the epidermis, so debridement needs
to be careful, gentle, thorough and wide
rather than aggressive, deep and radical,
which often leads to unnecessary removal
of the dermal tissue under the lesion. This
tissue is necessary for re-growth of healthy
horn and cornification. For debridement, I
use a small pair of rongeurs to remove the
bulk of diseased tissue, a sharp loop knife
and a #12 scalpel blade (Figure 8).
Figure 7: Frog surgically debrided.
Papillae can be seen but any hemorrhage has been wiped off. Note thin
strips of healthy tissue left intact
Figure 8: Tools / instruments used
to facilitate debridement.
After the bulk of the diseased tissue is
removed, the remaining layers of diseased
tissue just peel off in strips with the loop
knife and the blade is used in the tighter
more obscure areas. The debridement is
followed by cryotherapy to freeze the area
that has been debrided to remove residual bacteria from the surface in a double
freeze-thaw, freeze-thaw pattern using a
commercially available coolant spray.
Aftercare Of Canker
There are a variety of topical preparations that can be used following
debridement but the astringents (drying
agents) may play the most important role.
I use 4-inch x 4-inch gauze sponges moistened in a solution of 10% benzoyl peroxide
in acetone, sprinkled with metronidazole
powder placed over the debrided site. There
are other topical products available such as
dry dressings that have been soaked in a
solution of tricide/gentocin/lincomycin and
an oxytetracycline/metronidazole paste that
may be equally effective. No caustic preparations should ever be used as they will
burn or damage the dermal tissue trying
to restore healthy horn.
The foot is then bandaged using any
combination of products — baby diapers
attached with a cohesive bandage is a very
inexpensive option. A shoe with a treatment plate has become popular with canker
cases, but I feel it is contraindicated as it
neither keeps the foot as clean or as dry
as necessary post debridement. Once the
surface has a complete layer of thin cornification, a treatment plate can be used if
Client compliance. Owner compliance
for the aftercare is critical for a successful
outcome. The bandage is changed daily
for the first 7 to 10 days, and then at least
every second day. At each bandage change,
the affected area is cleaned gently with an
antiseptic solution (not antiseptic soap),
rinsed with free-flowing saline and dried
with a paper towel. The topical medication
of choice is applied and the foot is rebandaged. It is crucial to keep the animal in a
dry environment such as a small dry lot or a
stall bedded in saw dust or wood shavings
The owner should look for any focal
or small reoccurrences of disease in the
debrided surface at each bandage change. If
an area of abnormal growth is noted, these
are managed with light debridement using a
dry gauze sponge followed by cryotherapy.
The foot should be fully cornified within
3 to 6 weeks and a treatment plate can be
applied at that time if desired (Figure 9).
Figure 9: Before and after pictures of a canker case. After picture is 2 weeks post debridement.
Corticosteroids. There appears to be an
immune-mediated component to canker as
the corticosteroids make a profound difference in the outcome of the case. I put all
cases on a descending dose of oral prednisolone during the treatment phase of canker
(generally 4 weeks).3,4
I reported with Florida veterinarian John
Madison on 60 horses with canker in 2004
and then published an update on equine
canker with North Carolina State University
vet Rich Redding in Veterinary Clinics of
North America —Equine Practice in 2012.
I now have over 150 horses in the database.
The treatment of equine canker has always
presented a dilemma for veterinarians and
farriers due to the historically poor prognosis. The etiology of canker remains obscure.
However, the disease can be consistently
and effectively treated. It does not appear to
be a disease of horses caused by poor care or
unhygienic conditions. In the database, most
of the horses treated were well cared for
and received routine hoof care. While the
hind limbs seemed to be affected more frequently, forelimb involvement is common.
Trimming the foot, thorough debridement
and owner commitment are important for a
successful outcome of this condition. Careful
and thorough wide debridement of the lesion
is essential, rather than aggressive radical
debridement with the common connotation
“cut it all out.” The dermis has to be spared
in order for healthy epidermis to be produced
and cornified. Emphasis must be placed on
keeping the surgical wound clean and dry
until the defect has completely cornified.
Owner compliance to perform the daily
footcare is always a critical and essential
element in the treatment of equine canker.
Moyer, W.A., Colohan, P.T.: Canker. Equine
Medicine & Surgery, 5th edition, Mosby, St.
Louis (1999); 1544-1546.
O’Grady SE., Madison JM. How to
treat equine canker. Proceedings: Am
Assoc Equine Pract 2004; 50:202-205
Oosterlinck, M., Deneut, K., Dumoulin,
M., Gasthuys, F. and Pille, F.
Retrospective study of 30 horses with
chronic proliferative pododermatitis (canker). Equine Vet Educ, 2011;
Redding R., O’Grady SE. Nonseptic
Diseases Associated with the Hoof
Complex. Vet Clin N Am Equine 2012;