Managing Hoof Abscesses
Options for treating this frequent and frustrating cause of lameness
Reprinted with permission from the American Farrier Journal.
Original printed in the 2007 July-August issue of the American Farriers Journal
By Stephen E. O'Grady, DVM, MRCVS
Hoof abscesses are probably the
most common cause of acute
lameness in horses encountered
by veterinarians and farriers.
A hoof abscess can be defined as a
localized accumulation of purulent
exudates located between the germinal
and keratinized layers of the epithelium,
most commonly subsolar or submural.
Much debate still abounds between
the veterinary and farrier professions as
to who should treat a hoof abscess and
the best method in which to resolve the
Remember the origin of the organisms
that are responsible for a hoof
abscess gain entry through the hoof
capsule (epidermis) into the inner
subsolar /submural tissue (dermis) where
the organisms initiate an abscess. Foreign
matter (such as gravel, dirt, sand and
manure, coupled with infectious agents
such as bacteria or fungal elements)
generally gains entry into the hoof in one
of three ways:
- Through a break or fissure in the solewall junction (white line).
- A misplaced nail or a puncture wound somewhere in the solar surface of the foot.
- By way of a full thickness hoof wall crack or multiple old nail holes.
Formation Of An Abscess
|FIGURE 1. Abscesses form when foreign
debris gain entry and accumulate in a
small separation or fissure located in
the sole-wall junction anywhere around
the perimeter of the foot.
It may be easier for us to understand
how to treat an abscess if we briefly look at
the mechanism by which an abscess forms.
Foreign debris will gain entry and
accumulate in a small separation or
fissure located in the sole-wall junction
anywhere around the perimeter of the
foot, including the inner surface of the
bars adjacent to the sole (Figure 1).
As the animal bears weight, foreign
matter will migrate through the fissure
until it reaches the subsolar or submural
tissue (dermis). Once inside the hoof
capsule, the defense mechanism within
the dermal tissue recognizes the matter as
foreign and sets off a reaction. The
bacterium contained within the debris
invades the dermal tissue and leads to
inflammation, the bacteria continue to
grow and cause neutrophils (white cells)
to migrate into the area.
Enzymes released from the bacteria
and from the invading white cells lead to
liquefaction tissue necrosis and the development
of the gray/black exudate. The
inflamed area is quickly walled off with
a thin layer of fibrous tissue to form an
abscess. The inflammation and the pressure
from the accumulation of the
exudate exerted on the surrounding tissue
leads to the clinical signs associated with
a hoof abscess.
Dermal tissue can be inoculated by
bacteria from a misplaced nail in two
ways. The nail can be driven directly
into the laminar corium. When the nail
enters dermal tissue, the horse will show
discomfort as the nail is driven into the
foot and there will be hemorrhage
present where the nail exits the outer
Blood observed at the exit of the
offending nail will alert the farrier of the
misplaced nail and the blood also acts as
a "physiologic rinse" to dilute or eliminate
bacterial contamination. Removal of
the nail and application of an appropriate
antiseptic will usually prevent infection.
Another scenario that occurs frequently
is that while the farrier is driving a nail, the
horse shows pain indicating the nail is
invading sensitive tissue. The farrier will
generally remove the nail, place it in
another spot or direction and again drive it
into the foot. When this occurs, the farrier
should remove the shoe and examine the
spot where the nail entered the foot. When
a nail enters dermal tissue (even if
removed), it can seed the area with organisms
and lead to an abscess.
If the nail has entered the foot inside
the sole-wall junction, the owner should
be alerted as to potential problems and
the horse could be placed on a broadspectrum
antibiotic for 3 to 5 days as a
Finally, we have the condition
described as a "close nail" where the nail
is placed so that it lies against the border
of the dermal corium just inside the hoof
wall. Pressure against the corium, the
movement of the horse combined with
the organisms introduced with the nail,
will lead to an abscess as described
above. There is a lag period of 7 to 14
days or even longer before clinical symptoms
or discomfort is observed following
the placement of a "close nail."
Another common cause of perceived
subsolar abscesses is penetration of the
bottom of the foot (sole) by a sharp
object. This is not actually an abscess
but rather a diffuse infection caused by
the solar corium being seeded with organisms from the penetrating object.
Pain is immediate and usually
followed by infection within 3 days. A
full-thickness puncture wound in the sole
always requires veterinary input.
Most affected horses show sudden
(acute) lameness. The degree of lameness
varies from being subtle in the early
stages to non-weight bearing. The digital
pulse felt at the level of the fetlock is
usually bounding and the involved foot
will be warmer than the opposite foot.
With careful observation - unless the
abscess is in the middle of the toe - the
intensity of the digital pulse will be much
stronger on the side of the foot where the
abscess is located.
If the abscess is long standing, there
may be soft tissue swelling in the pastern
or above the fetlock on the side of the
limb corresponding to the side of the
foot where the abscess is located.
The site of pain can be localized to a
small focal area through the careful use of
hoof testers. Sometimes with acute lameness,
the pain will be noted over the entire
foot with hoof testers and, in this case,
veterinary assistance is used to rule out
laminitis, a severe bruise or even a
possible fracture of the distal phalanx (P3).
The most important aspect of treating
a subsolar/submural abscess is to establish
drainage. The opening should be of
sufficient size to allow drainage, but not
so extensive as to create further damage.
When pain is localized with hoof
testers, a small tract or fissure will
commonly be found in the sole wall junction
(white line). The wound or point of
entry may not always be visible, as some
areas of the foot such as the white line are
somewhat elastic and wounds in this area
tend to close. In this case, a suitable poultice
should be applied to the foot daily in
an attempt to soften the affected area and
eventually a tract will become obvious.
|FIGURE 2. Drainage of an abscess is
accomplished by opening the
offending tract or fissure using a thin
small loop knife, a 2 mm bone curette
or other suitable probe.
|FIGURE 3. A small opening created to
establish drainage. Note area of hoof
wall separation (so-called white line
disease) palmar to the draining tract.
The offending tract or fissure is
followed within the white line using a
thin small loop knife, a 2 mm bone
curette or other suitable probe (Figure 2).
The tract is slowly followed until a
gray/black exudate (pus) is released and
the probe will enter the "belly" of the
abscess. At this point, the tract is open
into the cavity of the abscess.
A small opening is all that is necessary
to obtain proper drainage (Figure
3). This can be determined by placing
thumb pressure on the solar side of the
tract and observing more drainage being
expressed or a bubble at the opening
when pressure is applied. Care should be
taken to avoid exposing any corium, as
it will invariably prolapse through the
opening, prevent closure of the tract and
create an ongoing source of pain. Under
no circumstances should an abscess be
approached through the sole.
The draining tract can be kept soft
and drainage promoted in many ways.
The application of an Animalintex poultice
that has been soaked in hot water is
applied for the first 24 to 48 hours has
been useful in the author's hands. This is
a self-contained, medicated poultice,
which is commercially available through
your veterinarian or tack shop.
The author prefers the sheet version of
this poultice rather than the poultice pad
distributed by this company, as the whole
foot, including the coronet, should be
enveloped in the poultice.
Using Soak Bandages
Another method to encourage
drainage is to apply a soak bandage. Here
layers of practical cotton are crisscrossed
to form a heavy bandage that envelops
the foot. MgSo4 (Epson salts) is placed
in the inner foot surface of the bandage
and the bandage is attached to the foot.
The bandage is now saturated with
hot water and saturated periodically over
the next 24 to 48 hours. Using either of
these methods eliminates the need for
continued foot soaking.
Ichthammol ointment is a coal tar
derivative with mild antiseptic properties
that has been described for treating skin
disease in both humans and animals. The
use of an Ichthammol bandage for
treating hoof abscesses, both before and
after drainage, has become another traditional
treatment among veterinarians and
horse owners with reportedly good
results. The author has not used this form
of treatment, therefore would be unable
to render an opinion as to its efficacy.
The tetanus immunization status of
the horse should always be determined.
The horse should show marked
improvement within 24 hours. Following
the poultice or foot soak bandage, the
hoof is kept bandaged with an appropriate
antiseptic such as Betadine solution/
ointment or 2 percent iodine until all
drainage has ceased and the wound is
dry. At this point, the opening is filled
with Keratex Hoof Putty that keeps the
affected area clean and prevents the accumulation
of debris within the wound. The
shoe is replaced when the horse is sound.
If The Infection Migrates
Many times the painful tract can be
located, but drainage cannot be established
at the sole-wall junction. In this
case, the infection is deep and may have
migrated under the sole or wall away
from the white line. Again, under no
circumstances should an opening be
created in the adjacent sole. This seldom
leads to the abscess, generally leads to hemorrhage and may create a persistent,
non-healing wound with increased potential
for bone infection.
Instead, a small channel can be created
on the hoof wall side of the white line
using a small pair of half-round nippers.
The channel is made in a vertical direction
following the tract to the point where
it courses inward. Drainage can usually
be established using a small probe in a
horizontal plane. Preferably this is done
at the onset of lameness, before the infection
ruptures at the coronet.
If left untreated, a hoof abscess will
follow the path of least resistance along
the outer margin of the dermal tissue and
eventually rupture at the coronet forming
a draining tract. Many horse owners actually
consider this to be an acceptable practice
and wait for this to take place. From
a humane standpoint, this practice often
extends the amount of time the animal
experiences severe pain.
Rupture at the coronet also leads to a
permanent scar under the hoof wall. This
tract leading to the coronet may result in
a prolonged recovery from the abscess, a
chronic draining tract, repeated abscesses
and a full-thickness, hoof-wall crack.
Every effort should be made to establish
drainage on the solar surface of the foot.
Abscess Or Infection?
Please be advised that the following
comments are the author's opinion and do
not reflect the position of the American
Association of Equine Practitioners
(AAEP) or any other veterinary medical
Members of the veterinary and farrier
professions have debated the topic of who
should treat hoof abscesses for ages. If we
go back and consider how an abscess is
formed, it is a cavity filled with exudate
surrounded by a thin fibrous membrane.
The cavity of the abscess could be
thought of as an extension of the entry
tract located in the hoof capsule.
Therefore, when a farrier follows a tract
through the sole-wall junction and creates
a small opening into the cavity of the
abscess, he or she may not be invading
There is no hemorrhage or pain
involved with this process. It could be
considered much the same as removing a
splinter from under the skin in a person.
In this context it would appear justified for
a farrier to drain an abscess and initiate the
aftercare described previously.
Again, it could be argued and/ debated
whether this is the practice of veterinary
medicine. Furthermore, it would be
prudent and in the farrier's best interest to
inform the horse owner at the onset as to
his or her intention of draining the
abscess, to give the owner the option of
contacting a veterinarian and explaining
to the owner that hoof abscesess can and
often do persist to a point where veterinary
intervention would be necessary.
On the other hand, when an infection
is present from a puncture wound in the
sole or a "close nail," the treatment should
be a joint venture with a veterinarian.
To establish drainage in this case, a
larger opening may need to be created
and sedation may be necessary, dermal
tissue will need to be invaded and
possibly debrided, there may be hemorrhage
and medications such as antibiotics
and anti-inflammatory drugs will need
to be prescribed.
If a farrier were to treat an established
infection in the hoof, it would be practicing
veterinary medicine and the farrier
could be held liable.
Prevention is achieved through proper
hoof care and centers on promoting a
strong, solid sole-wall junction (white
line) that resists penetration by debris.
Hoof abscesses are less likely to occur
when a solid sole-wall junction (white
line) is maintained.
Excessive toe length increases the
bending force exerted on the toe, leading
to a widening and weakening of the
white line. Other conditions that cause
mechanical breaks or weakness in the
continuity of the white line are hoof
capsule distortions (long toe-under run
heels, excessive toe length, heels too high
or a club foot, sheared heels), hoof wall
separations (white line disease, seedy
toe) and chronic laminitis. Excessive
moisture or dryness may also contribute
to weakness in the white line.
To prevent abscesses, it is important
that the foot be trimmed in a manner that
accentuates a strong healthy foot. A few
basic principles can be used when trimming
to create a strong foot and
strengthen the white line.
First is the creation of a good heel
base where the bars are preserved and the
heels are trimmed to the base of the frog,
or as far back as possible. This increase
in ground surface allows a substantial
amount of weight bearing to occur in the
palmar portion of the foot. Sole is only
removed adjacent to the white line to
identify excess hoof wall that should be
removed. It is not necessary to concave
the sole as this occurs naturally.
The toe is trimmed appropriately and
backed up from the dorsal surface (front)
of the hoof wall, such that a line drawn
across the widest part of the foot will be
in the middle of the foot.
This assures that there is no excessive
toe length. In some cases, fitting the
shoes hot may be helpful to seal the sole
wall junction. The use of hoof hardeners
(Keratex) and bedding the horse on shavings
or sawdust may be useful to harden
the feet during extremely wet weather or
when the horse is being washed
frequently, such as during horse shows.
During dry weather, a hoof dressing,
such as a combination of cod liver oil and
pine tar (mixed in a ratio of 3:1) painted
on the entire foot, may help to soften the
Preventing indirect penetration
through the white line is therefore
dependent on providing adequate protection
to the underlying sensitive structures.
The hoof capsule has a natural
ability to provide such protection and it
is imperative that we strive to enhance
these strong features through proper
trimming. Excessive removal of protective
horn is a common practice, as
emphasis is often placed on eye appeal
instead of functional strength.
Dr Steve O'Grady is both a veterinarian
and a farrier. He operates
Northern Virginia Equine in Marshall,
Va., which is an equine podiatry practice
and also offers a podiatry
consulting service. He is the chairman
of the AAEP veterinarian-farrier
committee and a member of the
International Equine Veterinarians
Hall of Fame.