Virginia Therapeutic Farriery

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 themost common cause of acutelameness in horses encounteredby veterinarians and farriers.

A hoof abscess can be defined as alocalized accumulation of purulentexudates located between the germinaland keratinized layers of the epithelium,most commonly subsolar or submural.

Much debate still abounds betweenthe veterinary and farrier professions asto who should treat a hoof abscess andthe best method in which to resolve theabscess.

Remember the origin of the organismsthat are responsible for a hoofabscess gain entry through the hoofcapsule (epidermis) into the innersubsolar /submural tissue (dermis) wherethe organisms initiate an abscess. Foreignmatter (such as gravel, dirt, sand andmanure, coupled with infectious agentssuch as bacteria or fungal elements)generally gains entry into the hoof in oneof three ways:

  1. Through a break or fissure in the solewall junction (white line).
  2. A misplaced nail or a puncture wound somewhere in the solar surface of the foot.
  3. By way of a full thickness hoof wall crack or multiple old nail holes.

Formation Of An Abscess

FIGURE 1. Abscesses form when foreigndebris gain entry and accumulate in asmall separation or fissure located inthe sole-wall junction anywhere aroundthe perimeter of the foot.

It may be easier for us to understandhow to treat an abscess if we briefly look atthe mechanism by which an abscess forms.

Foreign debris will gain entry andaccumulate in a small separation orfissure located in the sole-wall junctionanywhere around the perimeter of thefoot, including the inner surface of thebars adjacent to the sole (Figure 1).

As the animal bears weight, foreignmatter will migrate through the fissureuntil it reaches the subsolar or submuraltissue (dermis). Once inside the hoofcapsule, the defense mechanism withinthe dermal tissue recognizes the matter asforeign and sets off a reaction. Thebacterium contained within the debrisinvades the dermal tissue and leads toinflammation, the bacteria continue togrow and cause neutrophils (white cells)to migrate into the area.

Enzymes released from the bacteriaand from the invading white cells lead toliquefaction tissue necrosis and the developmentof the gray/black exudate. Theinflamed area is quickly walled off witha thin layer of fibrous tissue to form anabscess. The inflammation and the pressurefrom the accumulation of theexudate exerted on the surrounding tissueleads to the clinical signs associated witha hoof abscess.

Dermal tissue can be inoculated bybacteria from a misplaced nail in twoways. The nail can be driven directlyinto the laminar corium. When the nailenters dermal tissue, the horse will showdiscomfort as the nail is driven into thefoot and there will be hemorrhagepresent where the nail exits the outerhoof wall.

Blood observed at the exit of theoffending nail will alert the farrier of themisplaced nail and the blood also acts asa "physiologic rinse" to dilute or eliminatebacterial contamination. Removal ofthe nail and application of an appropriateantiseptic will usually prevent infection.

Another scenario that occurs frequentlyis that while the farrier is driving a nail, thehorse shows pain indicating the nail isinvading sensitive tissue. The farrier willgenerally remove the nail, place it inanother spot or direction and again drive itinto the foot. When this occurs, the farriershould remove the shoe and examine thespot where the nail entered the foot. Whena nail enters dermal tissue (even ifremoved), it can seed the area with organismsand lead to an abscess.

If the nail has entered the foot insidethe sole-wall junction, the owner shouldbe alerted as to potential problems andthe horse could be placed on a broadspectrumantibiotic for 3 to 5 days as aprophylactic measure.

Finally, we have the conditiondescribed as a "close nail" where the nailis placed so that it lies against the borderof the dermal corium just inside the hoofwall. Pressure against the corium, themovement of the horse combined withthe organisms introduced with the nail,will lead to an abscess as describedabove. There is a lag period of 7 to 14days or even longer before clinical symptomsor discomfort is observed followingthe placement of a "close nail."

Another common cause of perceivedsubsolar abscesses is penetration of thebottom of the foot (sole) by a sharpobject. This is not actually an abscessbut rather a diffuse infection caused bythe solar corium being seeded with organisms from the penetrating object.

Pain is immediate and usuallyfollowed by infection within 3 days. Afull-thickness puncture wound in the solealways requires veterinary input.

Clinical Signs

Most affected horses show sudden(acute) lameness. The degree of lamenessvaries from being subtle in the earlystages to non-weight bearing. The digitalpulse felt at the level of the fetlock isusually bounding and the involved footwill be warmer than the opposite foot.With careful observation - unless theabscess is in the middle of the toe - theintensity of the digital pulse will be muchstronger on the side of the foot where theabscess is located.

If the abscess is long standing, theremay be soft tissue swelling in the pasternor above the fetlock on the side of thelimb corresponding to the side of thefoot where the abscess is located.

The site of pain can be localized to asmall focal area through the careful use ofhoof testers. Sometimes with acute lameness,the pain will be noted over the entirefoot with hoof testers and, in this case,veterinary assistance is used to rule outlaminitis, a severe bruise or even apossible fracture of the distal phalanx (P3).

Treatment

The most important aspect of treatinga subsolar/submural abscess is to establishdrainage. The opening should be ofsufficient size to allow drainage, but notso extensive as to create further damage.

When pain is localized with hooftesters, a small tract or fissure willcommonly be found in the sole wall junction(white line). The wound or point ofentry may not always be visible, as someareas of the foot such as the white line aresomewhat elastic and wounds in this areatend to close. In this case, a suitable poulticeshould be applied to the foot daily inan attempt to soften the affected area andeventually a tract will become obvious.

FIGURE 2. Drainage of an abscess isaccomplished by opening theoffending tract or fissure using a thinsmall loop knife, a 2 mm bone curetteor other suitable probe.
FIGURE 3. A small opening created toestablish drainage. Note area of hoofwall separation (so-called white linedisease) palmar to the draining tract.

The offending tract or fissure isfollowed within the white line using athin small loop knife, a 2 mm bonecurette or other suitable probe (Figure 2).The tract is slowly followed until agray/black exudate (pus) is released andthe probe will enter the "belly" of theabscess. At this point, the tract is openinto the cavity of the abscess.

A small opening is all that is necessaryto obtain proper drainage (Figure3). This can be determined by placingthumb pressure on the solar side of thetract and observing more drainage beingexpressed or a bubble at the openingwhen pressure is applied. Care should betaken to avoid exposing any corium, asit will invariably prolapse through theopening, prevent closure of the tract andcreate an ongoing source of pain. Underno circumstances should an abscess beapproached through the sole.

The draining tract can be kept softand drainage promoted in many ways.The application of an Animalintex poulticethat has been soaked in hot water isapplied for the first 24 to 48 hours hasbeen useful in the author's hands. This isa self-contained, medicated poultice,which is commercially available throughyour veterinarian or tack shop.

The author prefers the sheet version ofthis poultice rather than the poultice paddistributed by this company, as the wholefoot, including the coronet, should beenveloped in the poultice.

Using Soak Bandages

Another method to encouragedrainage is to apply a soak bandage. Herelayers of practical cotton are crisscrossedto form a heavy bandage that envelopsthe foot. MgSo4 (Epson salts) is placedin the inner foot surface of the bandageand the bandage is attached to the foot.

The bandage is now saturated withhot water and saturated periodically overthe next 24 to 48 hours. Using either ofthese methods eliminates the need forcontinued foot soaking.

Ichthammol ointment is a coal tarderivative with mild antiseptic propertiesthat has been described for treating skindisease in both humans and animals. Theuse of an Ichthammol bandage fortreating hoof abscesses, both before andafter drainage, has become another traditionaltreatment among veterinarians andhorse owners with reportedly goodresults. The author has not used this formof treatment, therefore would be unableto render an opinion as to its efficacy.

The tetanus immunization status ofthe horse should always be determined.

The horse should show markedimprovement within 24 hours. Followingthe poultice or foot soak bandage, thehoof is kept bandaged with an appropriateantiseptic such as Betadine solution/ointment or 2 percent iodine until alldrainage has ceased and the wound isdry. At this point, the opening is filledwith Keratex Hoof Putty that keeps theaffected area clean and prevents the accumulationof debris within the wound. Theshoe is replaced when the horse is sound.

If The Infection Migrates

Many times the painful tract can belocated, but drainage cannot be establishedat the sole-wall junction. In thiscase, the infection is deep and may havemigrated under the sole or wall awayfrom the white line. Again, under nocircumstances should an opening becreated in the adjacent sole. This seldomleads to the abscess, generally leads to hemorrhage and may create a persistent,non-healing wound with increased potentialfor bone infection.

Instead, a small channel can be createdon the hoof wall side of the white lineusing a small pair of half-round nippers.The channel is made in a vertical directionfollowing the tract to the point whereit courses inward. Drainage can usuallybe established using a small probe in ahorizontal plane. Preferably this is doneat the onset of lameness, before the infectionruptures at the coronet.

If left untreated, a hoof abscess willfollow the path of least resistance alongthe outer margin of the dermal tissue andeventually rupture at the coronet forminga draining tract. Many horse owners actuallyconsider this to be an acceptable practiceand wait for this to take place. Froma humane standpoint, this practice oftenextends the amount of time the animalexperiences severe pain.

Rupture at the coronet also leads to apermanent scar under the hoof wall. Thistract leading to the coronet may result ina prolonged recovery from the abscess, achronic draining tract, repeated abscessesand a full-thickness, hoof-wall crack.Every effort should be made to establishdrainage on the solar surface of the foot.

Abscess Or Infection?

Please be advised that the followingcomments are the author's opinion and donot reflect the position of the AmericanAssociation of Equine Practitioners(AAEP) or any other veterinary medicalorganization.

Members of the veterinary and farrierprofessions have debated the topic of whoshould treat hoof abscesses for ages. If wego back and consider how an abscess isformed, it is a cavity filled with exudatesurrounded by a thin fibrous membrane.

The cavity of the abscess could bethought of as an extension of the entrytract located in the hoof capsule.Therefore, when a farrier follows a tractthrough the sole-wall junction and createsa small opening into the cavity of theabscess, he or she may not be invadingdermal tissue.

There is no hemorrhage or paininvolved with this process. It could beconsidered much the same as removing asplinter from under the skin in a person.In this context it would appear justified fora farrier to drain an abscess and initiate theaftercare described previously.

Again, it could be argued and/ debatedwhether this is the practice of veterinarymedicine. Furthermore, it would beprudent and in the farrier's best interest toinform the horse owner at the onset as tohis or her intention of draining theabscess, to give the owner the option ofcontacting a veterinarian and explainingto the owner that hoof abscesess can andoften do persist to a point where veterinaryintervention would be necessary.

On the other hand, when an infectionis present from a puncture wound in thesole or a "close nail," the treatment shouldbe a joint venture with a veterinarian.

To establish drainage in this case, alarger opening may need to be createdand sedation may be necessary, dermaltissue will need to be invaded andpossibly debrided, there may be hemorrhageand medications such as antibioticsand anti-inflammatory drugs will needto be prescribed.

If a farrier were to treat an establishedinfection in the hoof, it would be practicingveterinary medicine and the farriercould be held liable.

Prevention

Prevention is achieved through properhoof care and centers on promoting astrong, solid sole-wall junction (whiteline) that resists penetration by debris.Hoof abscesses are less likely to occurwhen a solid sole-wall junction (whiteline) is maintained.

Excessive toe length increases thebending force exerted on the toe, leadingto a widening and weakening of thewhite line. Other conditions that causemechanical breaks or weakness in thecontinuity of the white line are hoofcapsule distortions (long toe-under runheels, excessive toe length, heels too highor a club foot, sheared heels), hoof wallseparations (white line disease, seedytoe) and chronic laminitis. Excessivemoisture or dryness may also contributeto weakness in the white line.

Proper Trimming

To prevent abscesses, it is importantthat the foot be trimmed in a manner thataccentuates a strong healthy foot. A fewbasic principles can be used when trimmingto create a strong foot andstrengthen the white line.

First is the creation of a good heelbase where the bars are preserved and theheels are trimmed to the base of the frog,or as far back as possible. This increasein ground surface allows a substantialamount of weight bearing to occur in thepalmar portion of the foot. Sole is onlyremoved adjacent to the white line toidentify excess hoof wall that should beremoved. It is not necessary to concavethe sole as this occurs naturally.

The toe is trimmed appropriately andbacked up from the dorsal surface (front)of the hoof wall, such that a line drawnacross the widest part of the foot will bein the middle of the foot.

This assures that there is no excessivetoe length. In some cases, fitting theshoes hot may be helpful to seal the solewall junction. The use of hoof hardeners(Keratex) and bedding the horse on shavingsor sawdust may be useful to hardenthe feet during extremely wet weather orwhen the horse is being washedfrequently, such as during horse shows.

During dry weather, a hoof dressing,such as a combination of cod liver oil andpine tar (mixed in a ratio of 3:1) paintedon the entire foot, may help to soften thehoof capsule.

Preventing indirect penetrationthrough the white line is thereforedependent on providing adequate protectionto the underlying sensitive structures.The hoof capsule has a naturalability to provide such protection and itis imperative that we strive to enhancethese strong features through propertrimming. Excessive removal of protectivehorn is a common practice, asemphasis is often placed on eye appealinstead of functional strength.

Dr Steve O'Grady is both a veterinarianand a farrier. He operatesNorthern Virginia Equine in Marshall,Va., which is an equine podiatry practiceand also offers a podiatryconsulting service. He is the chairmanof the AAEP veterinarian-farriercommittee and a member of theInternational Equine VeterinariansHall of Fame.