How
to Treat Equine Canker
Stephen E. O’Grady, BVSc, MRCVS, John
B. Madison, VMD, Diplomate ACVS †
Reprinted with permission
from the American Association of Equine Practitioners.
Original printed in the 2004 AAEP Convention proceedings
Take-Home Message: The incidence of
equine canker appears to be more prevalent than once thought.
The treatments outlined in the literature for this disease
are sparse, varied and generally ineffective. The authors
outline a treatment protocol for canker, that when coupled
with owner compliance, will resolve the disease.
Introduction
Equine canker is described as an infectious process that
results in the development of a chronic hypertrophy of
the horn-producing tissues.1 It generally originates in
the frog; may remain focal, but has the capacity to become
diffuse and invade the adjacent sole, bars and hoof wall.
Canker can occur in one foot or multiple feet may be involved.
The disease is commonly seen in draft breeds but can affect
any breed or sex. Recently, one author (SEO) has seen
severe canker in two imported Warmblood horses. The etiology
of canker remains elusive but wet environmental or moist
unhygienic conditions have traditionally been thought
to act as a stimulus, however, canker is commonly seen
in horses that are well cared for and horses who receive
regular hoof care. One author (JBM) observed a seasonal
incidence of canker in Florida as the majority of cases
presented to his hospital were during the months of July
through December. The treatments described in the literature
have consisted of debridement and the application of topical
medications including antibiotics, astringents, antiseptics,
and caustic powders. No treatment to date has been consistently
effective in treating this disease and the prognosis has
always been guarded...
Clinical Signs
Canker generally originates in the frog and can be mistaken
for thrush in the early stages. Thrush is limited to the
lateral and medial sulci or the base of the frog if a
fissure is present whereas canker invades the horn of
the frog anywhere throughout its structure. There is a
proliferation of tissue with canker versus a loss of tissue
as with thrush. In the early stages canker may present
as a focal area of granulation tissue in the frog that
bleeds easily when abraded. Upon closer inspection a light
brown or grey tissue will surround this focal area (Fig
1).
If left untreated, the disease will become diffuse and
involve the frog, bars, sole and the stratum medium of
the hoof wall in the palmar/plantar aspect of the foot.
The infection results in abnormal keratin production or
dyskeratosis, which is seen as filamentous fronds of hypertrophic
horn.2 Canker is characterized by numerous small finger-like
papillae of soft off-white material that resembles a cauliflower-like
appearance (Fig 2).
1 The condition is frequently but not always accompanied
by a foul odor and is covered with a caseous white exudate
that resembles cottage cheese (Fig 3).
The frog is often undermined with the horny frog covering
the bulk of the disease. The affected tissue will bleed
easily when abraded and may be extremely painful when
touched. Varying degrees of lameness will be present depending
on the extent and depth of the infection. Most horses
are not lame when the disease is recognized and treated
early. The presence of lameness frequently indicates that
the disease involves more than the superficial horny frog
and warrants an aggressive approach to resolving the problem.
Diagnosis
A presumptive diagnosis of canker is based on the gross
appearance of the affected horny tissue along with a fetid
odor; 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 they appear in unusual locations of the foot. Care
must be taken to remove the superficial necrotic tissue
before the biopsy is taken from the margin of the lesion.
The biopsy should include both normal and abnormal tissue.3
A 6 mm biopsy punch works well. Histologically, the lesion
is read as a chronic, hypertrophic, moist pododermatitis
of the frog. 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.2 Cultures per se are unrewarding as they
typically produce an assortment of environmental organisms,
Bacteroides sp.and Fusobacterium necrophorum. 3, 4
Treatment
Canker always carries a guarded prognosis but recently
these authors have been successful with the following
approach. Treatment consists of thorough careful debridement
of the affected tissue followed by a regimen of topical
therapy applied daily and continued until the disease
is resolved. To debride the affected tissue, the horse
can be placed under general anesthesia or regional anesthesia
can be used with the horse standing. The horse’s foot
is trimmed appropriately removing all loose exfoliating
sole as well as any excess toe or heel. The use of a tourniquet
is essential. Firm pressure is placed across the vascular
bundles over the abaxial surface of the sesamoids using
either an Esmarch a bandage or simply a few tight turns
of a cohesive bandage. Debridement can be performed in
two ways. One author (JBM) uses electric cautery with
the horse under general anesthesia while the other author
(SEO) uses a sharp hoof knife and a number 12 scalpel
blade followed by cryotherapy with the horse standing.
All abnormal tissue is removed down to normal corium.
A clear demarcation will be seen between normal and abnormal
tissue. It is important not to remove excessive corium
as this will retard cornification following surgery and
may decrease the quality and depth of new sole being produced.
It may be helpful to remove 1-2cm of normal tissue around
the wound margins to ensure all abnormal tissue is removed.
5 If the decision has been made to place the horse under
general anesthesia, use of a typical cautery handle in
the cut mode allows accurate excision of hoof tissue including
frog and normal horny sole. The handle used in this way
will rapidly cut through sole and frog leaving only a
dry eschar behind. The cautery tip may be bent as needed
to undermine the base of the mass. Debridement can be
carried out in the same manner using a sharp hoof knife
and is followed by cryotherapy to freeze the area that
has been debrided. Liquid nitrogen has always been used
for this purpose but another practical method is to freeze
the debrided area with a coolant spray b that is available
for electrical circuits. The area of the foot that has
been debrided will be soft and pliable. Freeze this affected
area until the tissue becomes hard (known as hard freeze),
allow the area to thaw and then repeat the freeze once
more. Gauze 4 x 4 sponges soaked in a solution of 10%
benzoyl peroxide in acetone c and sprinkled with a fine
powder made by crushing metronidazole tablets with a mortar
and pestle or a pill grinder are then packed in the defect.
In large defects, to help insure contact of the medication
in the depths of the wound and to minimize the production
of exuberant granulation tissue, a putty elastomer material
is used to form an insert to fit in the bottom of the
foot (Fig 4).
The impression material should not extend below the bearing
surface of the hoof wall as this will create excessive
pressure and make the horse sore. The foot is then bandaged
with a dry bandage. The affected area is cleaned daily
with surgical scrub, rinsed with saline, dried with a
paper towel and the topical medication reapplied. It is
crucial to keep the animal in a dry environment. A shoe
with a treatment plate can also be used but it is sometimes
hard to keep the foot as dry as necessary with this method.
The authors prefer the use of bandages. Small reoccurrences
may be managed with the horse standing and local anesthesia
using either laser photoablation or cryotherapy. The use
of systemic antibiotics such as chloramphenicol or oxytetracycline
have been advocated but these authors question the use
as the cases treated have resolved with local treatment
only.4 A commitment is necessary from the owners, as aftercare
will take several weeks to months depending on the stage
of the disease until the affected tissue is cornified
(Fig 5).
Results
The records of 56 cases of canker that were
treated with the above protocol from 1998 - 2004 were
reviewed. The affected limb(s) were recorded in 54 cases.
There were 21 with forelimb involvement, 29 with hindlimb
involvement and one horse with one forelimb and one hindlimb
limb affected. Five horses were affected bilaterally.
Three horses were affected in all four limbs. Only one
reoccurrence was recorded and that horse was treated with
laser photoablation. Two horses are still undergoing treatment.
Discussion
The treatment of equine canker has always presented
a dilemma for veterinarians and farriers due to the poor
prognosis. The etiology of canker remains obscure; however,
the disease as seen by the authors differs in some respects
from the disease that was described in the old surgical
texts. It does not appear to be a disease of poorly cared
for horses. In fact most of the horses in the study were
well cared for and received routine hoof care. While the
hindlimbs seemed to be affected more frequently, forelimb
involvement is common. In the majority of cases, the condition
starts on the frog near the heel lateral or medial to
the sulcus. From that point, it can extend anywhere in
the foot and even break through the hoof capsule.
A variety of systemic and topical therapies have been
tried for canker. While a given treatment protocol would
seem to work in some instances, results were inconsistent.3
In 1997, one author (JBM) began using a topical therapy
reported by a Texas farrier consisting of benzoyl peroxide
in acetone and metronidazole.6 Since that time all horses
have been managed with surgical debridement followed by
this combination of topical therapy with excellent success.
The combination of thorough surgical debridement coupled
with topical benzoyl peroxide in acetone and metronidazole
have yielded consistent predictable results in 56 cases.
While the cause of canker remains obscure, there are several
principles of therapy for this condition for which the
authors consider to be important. Thorough debridement
of the lesion is essential. The method used to achieve
this is probably of less importance. Electrocautery or
cold steel excision followed by cryotherapy both cause
tissue necrosis away from the surgical margins ensuring
complete resection of the mass. It is important that the
entire mass be followed to its extent wherever it takes
you and removed. Lastly, methodical topical treatment
is important. Cleaning the affected area with an antiseptic
solution daily removes surface bacteria and provides an
environment conducive to wound healing, 10% benzoyl peroxide
in acetone is a excellent astringent and keeps the tissue
dry with no caustic effect and finally the bacteria cultured
from canker cases are usually anaerobic making metronidazole
a good choice as a topical antibiotic. Emphasis must be
placed on keeping the surgical wound clean and dry until
the defect begins to cornify. Owner compliance to perform
the daily foot care is another essential element in the
treatment of equine canker.
References
1) Moyer, W.A., Colohan, P.T.: Canker. In Equine Medicine
& Surgery, 5th edition, Mosby, St. Louis (1999); 1544-1546.
2) Reeves, M.J., Yovich, J.V., Turner, A.S. Miscellaneous
Conditions of the Equine Foot. In Veterinary Clinics of
North America – equine practice. Vol 5 (1) (1989); 236-237.
3) Wilson, D.G.: Equine Canker. In Current Therapy in
Equine Medicine 4. Edited by Robinson, N.E., W.B. Saunders
Co., Philadelphia (1997); 127-128.
4) Steckel, R.R.: Puncture Wounds, Abscesses, Thrush,
and Canker. In Current Therapy in Equine Medicine 2. Edited
by Robinson, N.E., W.B. Saunders Co., Philadelphia (1987);
271.
5) Turner, T.A.: Treatment of equine canker. Proc 34th
Annu Conv Am Assoc Equine Pract, 1988, pp 307-310.
6) Chapman B. Lubbock, TX. (personal communication)
a Medvet International, Libertyville, IL 60092
b Component Cooler, RadioShack Corp, Fort Worth, TX 76102
c Frank’s Pharmacy, Ocala, FL 34474
d Equilox Pink, Equilox International., Pine Island, MN
55963
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