DefinitionA hoof abscess can be defined as a localized accumulation of purulentexudate (pus) located between the subsolar (beneath the sole) or submural(beneath the wall) horn. The origin of the organisms responsible for a hoofabscess gain entry through the hoof capsule into the innersubsolar/submural tissue where organisms spread and initiate the formationof an abscess. Foreign matter (such as gravel, dirt, sand and manurecoupled with bacteria or fungal elements) generally gain entry into the hoofthrough a break or fissure in the sole-wall junction (white line) somewhereon the solar surface of the foot.

MechanismIt may be easier to understand how to treat an abscess by looking at how itforms. Foreign debris gains entry and accumulates in a small separation orfissure located in the sole-wall junction anywhere around the perimeter ofthe foot including the surface of the bars adjacent to the sole (Figure 1A &

Volume 15: Issue 4

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Hoof Abscesses

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by Stephen E. O’Grady, DVM, MRCVS

Hoof abscesses are probably the most common cause of acute severe lameness in horses. Often thefirst person to see a foot abscess is a farrier. There is still much debate between the veterinary andfarrier professions as to who is qualified to treat a hoof abscess and the best method in which toresolve the abscess. Considering a walled off hoof abscess is an extension of the epidermis (hoofcapsule), it is the author’s opinion the infection could be treated by either clinician.

1B). As the animal bears weight,pressure causes the foreign matter tomigrate through the fissure, creatinga tract, until it gains entry into thesubsolar or submural tissue (dermis).Once it reaches the dermis inside thehoof capsule, the foreign materialactivates the host’s immune systeminitiating an inflammatory responsewithin the dermal tissue. Thebacterium within the debris invadesthe dermal tissue, furtheraccentuating the inflammatoryresponse. As the bacteria divides,inflammatory cells (white cells) fromthe circulatory system are drawn tothe area. Enzymes released from thebacteria and from the invading whitecells lead to liquefaction tissuenecrosis and the development of pus.The infection is quickly walled offwith a thin layer of fibrous tissue toform an abscess. The inflammationand the pressure from theaccumulation of the pus exerted onthe surrounding dermal tissue leadsto the pain associated with a hoofabscess.Fig. 1A

Fig. 1B

Clinical SignsMost affected horses show suddensevere lameness. The degree oflameness varies from being subtle inthe early stages to non-weightbearing. The digital pulse felt at thelevel of the fetlock is typicallyincreased and the involved foot willbe warmer than the opposite foot.With careful observation, unless theabscess is in the middle of the toe,the intensity of the digital pulse willbe much stronger on the side of thefoot where the infection is located. Ifthe abscess is long standing, theremay be soft tissue swelling in thepastern up to or even above thefetlock on the side of the limbcorresponding to the side of the footwhere the abscess is located. Thesite of pain can be localized to asmall focal area through the carefuluse of hoof testers. Sometimes withacute lameness, the pain will benoted over the entire foot with hooftesters and, in this case, veterinaryassistance should be sought to ruleout laminitis, a severe bruise or evena possible fracture of the distalphalanx (P3).

TreatmentThe most important aspect oftreating a subsolar/submural hoofabscess is to establish drainage. Theopening should be of sufficient sizeto allow drainage but not soextensive as to create furtherdamage. When pain is localized withhoof testers, a small tract or fissurewill commonly be found in the solewall junction. The fissure or point ofentry may not always be visible assome areas of the foot, such as the

sole-wall junction, are somewhatelastic and tracts in this area tend toclose. In this case, a poultice shouldbe applied to the foot daily in anattempt to soften the affected areaand eventually a tract will becomeobvious.

When a tract or fissure is found, itcan be explored within the whiteline using a small thin loop knife ora 2mm bone curette until the tract isnarrowed down to a small opening(Figure 2A & 2B). The tract is thenfollowed using a horseshoe nail as adrill until pus is released and the nailenters the ‘belly’ of the abscess. Atthis point, the tract is open into thecavity of the abscess. A smallopening is all that is necessary toobtain proper drainage (Figure 3A &3B). This can be determined byplacing thumb pressure or hoof

testers on the solar side of the tractand observing more exudates beingexpressed or a bubble forming at theopening of the track when pressureis applied (Figure 4). Care should betaken to avoid exposing any dermis,as it will invariably prolapse throughthe opening, preventing closure ofthe tract and possibly creating an

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Fig. 2A

Fig. 2B

Figure 2A -Narrow loop knives

and bone curette.Figure 2B - Bevel of thehorseshoe nail makes a

good drill.

Fig. 3A

Fig. 3B

Fig. 4

Figure 3A & 3B - Nail inserted in‘belly’ of abscess.

Figure 4 - Thumb pressurepromotes drainage.

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ongoing source of pain. Under no circumstances should an abscess beapproached through the sole. It has to be remembered that organisms gainentry through the sole-wall junction not the sole. The difference is that apuncture wound through the sole leads to an infection under the solerather than an abscess migrating under the sole from the sole-walljunction.

The draining tract can be kept soft and drainage promoted in several ways.A poultice does not ‘draw’ out an infection as often described; rather apoultice will encourage drainage once it is established. The author willgenerally apply a medicated poulticea for the first 24-48 hours. Thepoultice is immersed in hot water, placed on the foot and attached with aroll of wide brown gauze, a cohesive bandage and waterproof tape. Thesheet version of this poultice is preferred rather than a poultice pad whichjust covers the solar surface of the foot. The whole foot including thecoronet should be enveloped in the poultice. Another method toencourage drainage is to apply a soak bandage, where layers of practical(pound) cotton are stacked together, enveloping the foot and forming aheavy bandage. Epson Salts (MgSO4) is placed on the inner foot surface ofthe bandage and the bandage is attached to the foot as described above.The bandage is now saturated with hot water and saturated periodicallyover the next 24-48 hours. Using either of these methods eliminates theneed for foot soaking.

There are numerous commercial products marketed to treat foot abscessesbut these products will only be helpful if they compliment the principlesof drainage described above.

AftercareOnce drainage is established the horse should show marked improvementwithin 24 hours. Once drainage has ceased, the hoof is kept bandaged withan antiseptic solution / ointment or 2% iodine applied over the tract untilthe wound is dry and sealed. When dry and sealed, the opening of thetract is filled with a medicated hoof puttyb which keeps the affected areaclean and prevents the accumulation of debris within the tract or wound.The shoe is replaced when the horse is completely sound.

A persistent hoof abscessOften, a painful tract can be located but drainage cannot be established atthe sole-wall junction. In this case, the infection is deep and may havemigrated under the sole or wall away from the sole-wall junction or whiteline. Again, under no circumstances should an opening be created in theadjacent sole. Invading the sole seldom leads to the abscess and often leadsto hemorrhage and may create a persistent, non-healing wound withpotential for osteomyelitis of the distal phalanx (P3). Instead, a small

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channel can be created on the hoof wall side of thesole-wall junction using a small pair of half roundnippers. The channel is made in a vertical directionfollowing the tract to the point where it coursesinward. Drainage can usually be established using asmall probe or horseshoe nail in a horizontal plane.Preferably, this is done at an early stage of thelameness before the infection ruptures at the coronet.

If left untreated, a hoof abscess will follow the path ofleast resistance along the outer margin of the dermaltissue and eventually rupture at the coronet forminga draining tract. Many horse owners actuallyconsider this to be an acceptable practice and elect towait for this to take place. This practice often extendsthe time the animal experiences severe pain. Ruptureat the coronet leads to a permanent scar under thehoof wall. The tract leading to the coronet may alsoresult in a prolonged recovery from the abscess, achronic draining tract, repeated abscesses andeventually a full thickness hoof wall crack. Effortshould be made to establish drainage on the solarsurface of the foot prior to a rupture at the coronet.

Infection from a misplaced horseshoenailDermal tissue can be inoculated by bacteria from amisplaced nail or so called ‘hot nail’ in two ways. Thenail can be driven directly into the laminar corium.When the nail enters dermal tissue, the horse willgenerally show discomfort and there will behemorrhage present where the nail exits the outerhoof wall. Blood observed at the exit of the offendingnail will alert the farrier of the misplaced nail. Theblood also acts as a “physiologic rinse” to dilute oreliminate bacterial contamination. Removal of thenail and application of an antiseptic will usuallyprevent infection and is generally all that is necessary.Another scenario that occurs frequently is while thefarrier is driving a nail, the horse shows discomfortindicating the nail is invading dermal tissue. Oftenthe farrier will remove the nail, place it in anotherspot/direction and again drive it into the foot.However, when this scenario occurs, the farriershould remove the shoe and examine the spot wherethe nail entered the foot. If a nail enters dermal tissue

(even if removed), it causes trauma to the dermaltissue and can seed the area with organisms whichmay lead to abscess formation. If the nail has enteredthe foot inside the sole–wall junction, theowner/trainer should be alerted to the potentialproblems and the horse could be placed on an oralbroad spectrum antibiotic for 3-5 days as aprophylactic measure.

Lastly, we have the condition described as a “closenail” where the nail is placed such that it lies againstthe border of the dermal tissue just inside the hoofwall. Pressure against the corium combined withconstant movement of the nail against the dermis asthe horse bears weight may cause an inflammatoryresponse and allow any bacteria that were introducedwith the nail to divide and form an abscess asdescribed above. There is a lag period of 7-14 days oreven longer before clinical symptoms or discomfortis observed following the placement of a “close nail.”Treatment again would be to establish and promotedrainage. ■

Dr. Steve O’Grady is a veterinarian and a farrier. He operatesVirginia Therapeutic Farriery which is a referral practicedevoted to therapeutic farriery located in Keswick, VA.

Disclaimer: Dr. O’Grady has no financial interest in FarrierProducts Distribution (FPD) or any products described in thisarticle.

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REFERENCESRedding WR, O’Grady SE. Septic Diseases Associated with theHoof Complex: Abscesses and Punctures Wounds. In O’Grady,SE, Parks, AH, ed. The veterinary clinics of North America:Equine Practice. 2012 vol. 28:2. Philadelphia: W.B. Saunders, pp423-440.

FOOTNOTESa. Animalintex poultice, 3M Companyb. Keratex Medicated hoof putty

GLOSSARYEpidermis – the outer most and nonvascular layer of the hoofcapsuleDermis – layer of tissue that liesbeneath the epidermis … containsnerves and blood vessels

A full Glossary of TherapeuticFarriery Terms is available on FPD'swebsite farrierproducts.com underthe Farrier Education Tab; or onFPD's Field Guide for Farriers atfarrierproducts.com/fieldguide.

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