|
Hoof
Abscesses
Stephen E. O'Grady, DVM, MRCVS
Hoof abscesses are probably the
most common cause of acute lameness in horses. Foreign matter
(such as gravel, dirt, sand, etc.) or infectious agents
such as bacteria or fungal elements gains entry into the
hoof through a separation in the sole-wall junction (white
line). This foreign debris will migrate in the hoof to the
sensitive subsolar or submural tissue leading to infection.
Another common cause of subsolar abscesses is penetration
of the bottom of the foot (sole) by a sharp object. Infection
may also gain entry into the foot by way of a hoof wall
crack or multiple old nail holes.
Hoof abscesses are less likely to occur with a solid sole-wall
junction (white line). Conditions that cause mechanical
breaks or weakness in the continuity of the white line are
hoof imbalance (long toe-underrun heel syndrome, excessive
toe length, heels too high) hoof wall separations (white
line disease, seedy toe), aggressive removal of sole and
chronic laminitis. Excessive moisture or dryness may also
contribute to weakness in the white line. If left untreated,
the subsolar abscess will follow the path of least resistance
up the hoof wall, rupture and then form a draining tract
at the coronet. This often leads to a permanent scar in
the hoof wall.
Clinical Signs
Most affected horses show sudden (acute) lameness. The degree
of lameness varies from subtle 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. The site of pain can be localized through the use
of hoof testers. A small tract or fissure will commonly
be observed in the white line where the pain is noted. The
wound or point of entry may not always be visible, as some
areas of the foot such as the white line and frog are somewhat
elastic and wounds in these areas typically close. Sometimes
pain will be noted over the entire foot with hoof testers
and, in this case, the veterinarian may want to rule out
a severe bruise or a possible fracture of P3 (coffin bone)
Treatment
The object of treating a simple subsolar abscess is to open
and drain the infection. The opening should be of sufficient
size to allow drainage but not so extensive as to create
further damage. Establishing drainage is the most important
aspect of therapy. Preferably, this is done at the onset
of lameness before the infection ruptures at the coronet.
The offending tract or fissure is opened on the hoof wall
side of the white line using a 2 mm bone curette or other
suitable probe. A small opening is sufficient to obtain
proper drainage and care must be taken to avoid exposing
solar corium, as it will invariably prolapse through the
opening and create an ongoing source of pain. The draining
tract is kept soft and drainage is enhanced by the application
of an Animalintex® poultice for the first 48 hours. This
is a self-contained, medicated poultice, which is commercially
available through your veterinarian or tack shop. In most
cases, this eliminates the need for continued foot soaking.
The horse should show marked improvement within 24 hours.
The hoof is kept bandaged with a suitable antiseptic such
as Betadine® ointment or 2% iodine until all drainage has
ceased and the wound is dry. At this point, a small gauze
plug is used to fill the opening of the tract and is held
in place with super glue. This keeps the affected area clean
and prevents the accumulation of debris within the wound.
The shoe is replaced when the horse is sound. Many times
the painful tract can be located but drainage cannot be
established at the white line. In this case, the infection
has migrated under the sole away from the white line.
Under no circumstances should an opening be created in the
adjacent sole. This only leads to a persistent, non-healing
wound and increased susceptibility to bone infection. Instead,
a small channel should be made on the hoof wall side of
the white line in a vertical direction following the tract
to the point where it courses inward. Drainage can be established
here in a horizontal plane. Tetanus immunization status
of the horse should be determined. Use of systemic antibiotics
is optional and based on the needs of the individual horse.
Prevention
Prevention is achieved through proper hoof care and centers
around promoting a strong, solid white line which resists
penetration by debris. Excessive toe length increases the
bending force exerted on the toe, leading to a widening
and weakening of the white line. This, along with toe cracks
and hoof wall separations, is the most common cause of foot
abscesses.
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, the bars of the
foot are left untouched and the heels are trimmed back toward
the widest part of the frog, or as far back as possible.
This allows a large amount of weight bearing to occur in
the posterior portion of the foot and not the toe area.
Sole is only removed adjacent to the white line to identify
excess hoof wall to be removed. It is not necessary to concave
the sole as this occurs naturally. The toe is then backed
up from the dorsal surface (front) of the hoof wall and/
or the breakover is set back accordingly. This assures that
there is no excessive toe length. A good rule of thumb to
use when trimming the foot is to leave the last few rubs
on the bottom of the foot. When applying shoes, fitting
the shoes hot may be helpful to seal the sole wall junction.
The use of hoof hardeners (Keratix®) 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 contain moisture.
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.
|
|
|
