E d i t o r ’s Note: This art i cle by Michael Wildenstein recounts a recent study heconducted to isolate the cause of hoof wall sep a ration at t ri bu t able to wh i t eline disease and to thereby va l i d ate a tre atment ap p ro a ch. Wildenstein is theresident fa rrier in the College of Ve t e ri n a ry Medicine at Cornell Unive rs i t yin Ithaca, N ew Yo rk. He is a cert i fied journ eyman fa rrier and a fe l l ow of theWo rshipful Company of Fa rri e rs of Gre at Bri t i a n .

By Michael Wildenstein CJ, FWCF

WE CAN NOW SAY with confidence that we have a safe and effe c t ive tre at-ment method for white line disease, wh i ch is a fungal infection of a hors e ’sh o o f. More specifi c a l ly, my study eliminated any doubts that hoof wall sep a-rations at t ri bu t able to white line disease are caused by fungi that can bet re ated with a ch l o rine dioxide solution.

F u n gi have long been thought to be a cause of white line disease,but bacteri aor yeast have also been bl a m e d. Previous studies did not pinpoint the infe c t i o u sagent with cert a i n t y, l e aving the most effe c t ive tre atment method also open to ques-tion. The doubts surrounding the disease are mirro red in the many names by wh i chit has been known through the ye a rs.

December, 2003 AMERICAN FARRIERS JOURNAL www.americanfarriers.com 45

“A great number of bacteria andfungi have been incriminated

in the pathophysiology, butsample collection techniquesused in previous studies have

been open to criticism...”

A DVANCED LESIONS.The integrity and weight-bearing capability of a hoof can be destroye dby advanced lesions caused by fungi.

SOLAR V I E W.Lesions of the stratum medium asseen from the solar surface of the hoof. In suchcases a fungal infection creating a cavity maybe secondary to an injury, abscess or laminitis.

Historical PerspectiveThe term “ white line disease”has been

given to the progre s s ive sep a ration of thehoof wall of the hors e. The term is usedp ro m i n e n t ly today, though it is used inter-ch a n ge ably with “ o ny ch o my c o s i s ” t od e s c ribe the cavities fo rmed in the hoofwall by fungal activ i t y. Ony ch o my c o s i sis derived from Latin. Ony ch means cl awor nail, mycosis means infection ordisease caused by a fungus.

In 1864,Antonio Pires described hoofwall sep a ration and its tre atment. Hisa n atomical description of the wall sep a-rations we re accurate and define thecondition in the hors e ’s hoof that we callwhite line disease.

In 1884, A. Lungwitz descri b e d“ h o l l ow wa l l ” as a sep a ration betwe e nthe middle layer of the wall and the ke ra-p hyllous laye r. Lungwitz said the condi-tion was ra re and that the cavity wa su s u a l ly filled with cru m p l i n g, d i s i n t e-grated horn.

In 1897, A . W. Dollar, M R C V S,d e s c ribed the condition as “loose wa l l ,”a ra re condition. Dollar said the conditionwas due to a fungus-like organism thate n t e red the inner sheath of the wall andinduced ch a n ge in the horn. In 1903,P ro f.

William Russell re fe rred to the conditionas “ foot ro t ” or “ s e e dy toe,” wh i ch mani-fests itself in the wasting away or dry i n gup of the sensitive laminae.

S ke t ches by Russell and Pires accu-rat e ly depict lesions in the strat u mmedium as we see them today. Th elesions start at the toe quart e rs and spre a din a proximal palmar direction and affe c tthe innermost stratum medium.

Modern DescriptionsTra cy A. Tu rn e r, DV M , M S, D i p l .

AC V S, found the condition re fe rred to asa yeast infe c t i o n , candida and hoof ro t .Rob Siga fo o s , fa rrier at the Unive rsity ofPe n n s y l vania ve t e ri n a ry sch o o l , re fe rred tothe condition as “ s u b d u ral ero s ive lesion.”

In 1995, Doug Butler PhD, C J F,F W C F, d e s c ribed a progre s s ive podo-d e rm atitis that ap p e a red like a gra nu l at e dcheese mixture, wh i ch was the dige s t e ds t ratum medium left behind from thef u n gi. When the residue was culture d, as m o rga s b o a rd of fungi was fo u n d.

Hoof wall sep a ration is mentionedf re q u e n t ly in modern fa rrier literat u re.H i ck m a n ’s Fa rri e ry, 1 9 9 7 , d e s c ri b e d“ s e e dy toe” as a cavity between the hornyand sensitive laminae filled with a mealy

type of horn. This description fits thec ri t e ria for ony ch o mycosis because ofthe cavity descri b e d.

D r. Ric Redden is said to have coinedthe term “ white line disease” to descri b ea sep a ration of hoof wall that is distinctf rom laminit is. Fa rrier Burn eyC h ap m a n , who spent more t imes t u dying the condition than anyone else,re fe rred to it as ony ch o my c o s i s , wh i chis well known in human medicine andre fe rs to a fungal infection affecting thetoenails or fi n ge rnails. It may invo l vea ny component of the nail unit incl u d i n gthe nail mat rix. Sometimes trauma ord a m age to a nail predisposes the deve l-opment of the condition.

The term ony ch o mycosis is ap p ro-p ri ate for horses when the disease is af u n gal infection of the hoof wa l l ,u s u a l lys e c o n d a ry to mechanical stresses re l at e dto injury, poor management or otherdisease pro c e s s e s .

Foot Structure and TermsThe wall of the hoof grows from the

epithelium cove ring the coro n a ry derm i s .It consists of horn tubules that aree m b e dded in the intert u bular horn ,wh i chis at t a ched to the coffin bone and hoof

46 AMERICAN FARRIERS JOURNAL www.americanfarriers.com December, 2003

“We hypothesize that mechanical stress created by excessive toe length, laminitis, poor management or injury predispose horses to the collection of environmental contaminants

within the stratum medium. All of the identified fungi can be cultured from soil and wood...”

Careful management of equine stables and the picking of thehooves on a daily basis will reduce the incidence of fungalinfections of the hoof responsible for white line disease.

In humans, toenail fungus commonly affects the trau-matically stressed toes of runners, and the treatment isfocused on the fungal infection rather than the mechanicalstresses produced by running. Because a horse depends onthe integrity of the hoof wall to stand or move, the focus hereis prevention.

All of the horses with a severe fungal infection in the studydetailed in the accompanying article had previous damageto the hoof. The damage was created by laminitis, anabscess, hoof wall avulsions or cracks, and horseshoe nails.

Hot seating horseshoes in the application process willeliminate the fungi between hoof and shoe, thus decreasingthe risk of transporting fungal spores into the hoof wall withthe horseshoe nail.

The application of shoes on hooves with avulsions orcracks will help protect the affected area by preventing abuildup of debris.

Reducing the use of hoof pours or urethane packing(which create an environment condusive to fungal growth)will reduce fungal activity. Properly placed shoes will protectthe hooves from the breaks and splits that provide access forfungal spores.

Soaking laminitic or abscessed feet with chlorine dioxidewill prevent serious fungal infections. The use of iodine onthe sole will reduce fungal populations. Fungi can consumethe insensitive sole, leaving little or no natural protection.

Using a hoof antiseptic with povidine iodine will likewiseprotect the hoof from serious fungal lesions. Activity andmovement of the horse improves circulation and the body’sdefense against fungal and bacterial infections.

—Michael Wi l d e n s t e i n

PREVENTING WHITE LINE DISEASE

c a rt i l ages. The three basic laye rs of thewall stru c t u re consist of the strat u mex t e rnu m , medium and internum.

The stratum ex t e rnum consists ofh o rn tissue produced by the peri o p l i cd e rm i s , wh i ch lies dire c t ly proximal tothe coro n a ry dermis. The strat u mex t e rnum is only a few millimeters thickand is somewh at ru bb e ry near the coro-n a ry band and is dehy d rated over thedistal hoof wall. The bulk of the hoofwall is made up of the pigmented hornt u bules of the stratum medium. Th enonpigmented stratum internum consistsof ap p rox i m at e ly 600 laminae that inter-d i gi t ate with the sensitive laminae of thelaminar derm i s .

The dermis of the sole is fi rm lyat t a ched to the unders u r face of the coffi nbone and produces a mixture of hornt u bules and intert u bular horn. The junc-tion between the sole and the wall is thewhite line (zona alba). The white linei n cludes some of the non-pigmented

s t ratum medium of the wa l l , the distalends of the horny laminae and thepigmented horn produced over thet e rminal papilliae of the laminal derm i s .

The condition is re s t ricted to thei n n e r-most area of the stratum medium.This area has a moisture content of 75p e rcent in a normal hoof. The fi rst indi-c ation would be a sep a ration betwe e nsole and wall as viewed from the solars u r fa c e. Mat e rial re m oved from the sep a-ration with a thin probe will yield dirt ,m a nu re, d i gested horn and residue thatre s e m bles dry ch e e s e.

The sep a ration may advance to thec o ro n a ry corium. The extent of the sep a-ration can be seen by taking ra d i ograp h s .By ge n t ly tapping on the hoof wall thea ffected area will sound hollow. In ach ronic case, a bu l ge will be present inthe hoof wall at the most proximal pointof the infection. As with all fungal infe c-tions of the hoof wa l l , a distinct odorwill be pre s e n t .

The ControversyWhite line disease has been a deb at e d

issue for ye a rs and has been a source ofcontention among fa rri e rs and ve t e ri n a r-ians. A gre at number of bacteria andf u n gi have been incri m i n ated in thep at h o p hy s i o l ogy, but sample collectiont e chniques used in previous studies havebeen either unrep o rted or open to cri t i-cism for possibly allowing contamina-tion of the samples.

Th e re is one rep o rt in the ve t e ri n a ryl i t e rat u re (Pat h o m o rp h o l ogical Fi n d i n g sin a Case of Ony ch o mycosis of aR a c e h o rs e, by Ku wa n o , et al, f rom theJapan Racing A s s o c i at i o n , Jo u rnal ofVe t e ri n a ry Medical Science 58 (110:1 1 1 7 - 1 1 2 0 , 1996)) that demonstrat e s ,with histopat h o l ogy, t h at disease of thewhite-line area is caused by a fungus.

In the 1990s, B u rn ey Chapman urge dh o rs e s h o e rs to send samples from lesionsin horses hooves to Mt. Sinai Medical

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By Michael Wildenstein

The most effective treatment of white line disease(onychomycosis) requires removal of the affected tissue andsterilization of underlying tissue, followed by antifungaltreatments.

The use of antifungals alone produces negative resultsuntil the overlying hoof wall is removed. The removal ofportions of the hoof wall allows the antifungals to be applieddirectly to the fungal infection. Antifungal drugs such asmiconazole, clotrimazole and itraconazole are of benefit.

Exposing The LesionThe most important aspect of treatment is carefully

removing all affected tissue and cleaning the area. It isimportant that the wall is not pulled or pried off as this coulddamage the laminae. Removal of the hoof wall over thelesion is safely done with a half round nipper, a rasp and abone curet. The curet is helpful when opening the smallerregions of the lesion. The lesion is identified by the chalkysubungual material.

The area is then cleaned by soaking the affected hoof ina solution of chlorine dioxide at 20,000 parts per million. Itis important to soak the hoof using a bag or innertube toprevent the gas from the solution from escaping. The gas iseffective in reaching the fungal spores on the hoof.

Chlorine dioxide is safe at 20,000 ppm and does not affectthe hoof in a negative way. Hoof ailments such as thrush andcanker have fungal and bacterial agents that are also elimi-nated with chlorine dioxide. Dentists use it to treat bacte-rial, fungal and yeast infections of the mouth, and it is also

used in the food industry for cleaning vegetables and by foodprocessing plants.

Soaking The HoofSoaking the hooves is done on a weekly basis until the

lesion is grown out. It is also important to check the hoof foractive lesions on a weekly basis to avoid progression of lesionsnot found during the initial debridement.

Covering the affected area with a hoof patch is contraindi-cated because fungal spores can be trapped, producinganother lesion.

The lesion is covered with felt to protect the hoof andallow for the introduction of antifungals.

The application of a hoof cast to protect the hoof when asignificant portion of the hoof has been removed will bebeneficial. The hoof cast is temporary and should be checkedon a daily basis for irritation to the heel bulbs. The cast will needto be removed within 21 days. The application of a castrequires the horse to be stalled in a clean and dry environment.

Shoeing May HelpA shoe can be applied to the cast to prevent wear and

further protect the hoof. A treatment boot or hoof boot maybe of temporary help during the treatment period.

If enough hoof wall exists to allow for nailing a supportshoe to the hoof, it will provide more permanent protectionthan a cast or hoof boot. Nail holes can be punched in theshoe to allow for nailing to healthy wall. Clips on the horse-shoe will stabilize the shoe and prevent stress on the existinghoof wall. The application of a shoe will ease the soaking andmedicating process.

TREATING WHITE LINE DISEASE

Center to be analy zed by Susan Sharp ,P h . D. She cultured 156 sep a rate fungif rom 100 samples. Chapman defined thedisease as a fungal infection of the hoofwall secondary to mechanical stre s s e sre l ated to poor management or otherdisease pro c e s s e s .

L ay equine literat u re and fa rrier tra d ej o u rnals contain many anecdotal rep o rt sand uncontrolled mini-studies postulat i n ga gre at number of causes and pre d i s-posing fa c t o rs of hoof wall sep a rat i o n .

In 2000, a study done by M. Ke l l e r, S.K re h o n , C. Stanek and R. Rosenga rt e nfound 26 species of molds and fivespecies of derm at o p hytes on 187 hoove s .This study as well as others show a gre atva riety of fungi on the horses hoove s .

But the questions re m a i n e d : Is thedisease a pri m a ry or secondary infe c t i o ncaused by bacteri a , by fungi , or both? Ifit is secondary, wh at are the pre d i s-posing fa c t o rs?

Study OverviewPoor hoof quality can result fro m

ge n e t i c s , e nv i ro n m e n t , m a n age m e n t ,nu t rition and infectious agents. The go a lof this study was to define one type off u n gal lesion and to secure samples take nin a way that the pri m a ry fungi could becollected while ruling out yeast andb a c t e rial fa c t o rs .

In an effo rt to isolate the causat ivefactor in hoof wall lesions, one type ofl e s i o n , hoof wall sep a rat i o n , was studied.The type of hoof wall lesions looked at

in this rep o rt we re cavities cre ated byf u n gi in the innermost stratum mediumof the hoof wall. These lesions can cre at el a rge voids that can sep a rate the wa l lf rom the laminae that connects the hoofwall to the third phalanx. This type oflesion can have deva s t ating effects onthe integrity of the hoof wa l l .

In an effo rt to identify the infe c t i o u sage n t s , I took samples from poor qualityh o oves and had them examined for thep resence of fungi and bacteria.

Case SelectionAll horses presented to the fa rri e r

s e rvice we re eva l u ated for the cl i n i c a lsigns of “ white line disease.”The hoove si d e n t i fied as having a visible sep a rat i o nof hoof wall with a dry / ch a l ky tex t u re orthose with bu l ges and ab n o rmal perc u s-sion we re selected for the study.

A total of five infected hooves we reeva l u at e d, with the ave rage age of 5 ye a rso l d. The hooves we re of four ge l d i n g sand one mare. These horses had visibl es ep a ration of hoof wall with a dry / ch a l kyt ex t u re or wall bu l ges and ab n o rm a lp e rcussion.

Four horses determined to have nohoof irreg u l a rities or lesions we reselected for the control gro u p .

Careful Sample CollectionOn the diseased hoove s , the leading

e d ge of the lesion was found by usinghoof wall percussion and ra d i ograp h s .In all suspected cases, t h e re was a distinct

h o l l ow sound to percussion that disap-p e a red half the distance or gre ater fro mthe sole to the coro n a ry band.

A marker was placed at the point thatthe percussion ch a n ge d, and ra d i ograp h swe re used to ve rify the edge of the lesion.Samples we re taken at that point.

An attempt was made to steri l i ze thehoof wall prior to sample collection. Th ehoof wall was painted with concentrat e dfo rm a l d e hyde three times, with 5m i nutes between ap p l i c ations.

At that time, a 1-centimeter diameterp o rtion of the stratum ex t e rnum wa sre m oved with a steri l i zed dremel bit andthe fo rm a l d e hyde ap p l i c ation wa srep e ated with a final swabbing ofc o n c e n t rated iodine placed on the cre at e dwall defe c t .

The hoof wall and pastern we re thenc ove red with an iodine impreg n at e ds u rgical sticky drape and a small windowwas cut out over the cre ated wall defe c t ;s t e rile surgical gloves we re wo rn. Steri l ebone curettes we re used to re m ove thes t ratum medium.

Ap p rox i m at e ly 70 percent of thes t ratum medium was re m ove d, reve a l i n gthe edge of the lesion. The strat u mmedium re m oved for culture was dryand ch a l ky and not of normal tex t u re ori n t egri t y. The mat e rial was tra n s fe rre dinto a sterile container for culture.

All samples we re asep t i c a l lysubmitted to the New Yo rk Stat eD i agnostic Lab o rat o ry for aero b i c / a n a e r-obic bacterial and fungal culture.

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COMPLETE REMOVAL.The dorsal hoof wall over the lesionwas completely removed in this case to provide access toand elimination of the cavity-causing fungi.

AVOIDING CONTA M I N AT I O N . Here the hoof is sterilized andan iodine-impregnated surgical sticky drape is applied.

Fungi FoundThe four control hooves did not grow

a ny bacteria or fungi , wh e reas the fivediseased hooves grew four types of fungi .The same species of fungi we re found insamples taken from soil. The hooves withlesions did not grow any bacteri a .

Foot B a c t e rial F u n gal N o . C u l t u re C u l t u re

1 . No growth Tri ch o d e rma sp2 . No growth Mucor sp3 . No growth A s p e rgillus

g l a u c u s4 . No growth G l i o cladium sp5 . No growth G l i o cladium sp

Preliminary ConclusionThe fact that all of the controls we re

n egat ive for both bacterial and funga lgrowth va l i d ates the sample acquisitionas a methodology for collection of steri l esamples of the stratum medium fo rc u l t u re. The absence of bacteria and posi-t ive growth of fungi supports the role ofa fungal infection and, t h e re fo re,s u p p o rts the term “ o ny ch o my c o s i s ” i nd e s c ribing this disease.

All four species of fungi cultured arek n own to be ke rat i n o p h i l i c. This doesnot mean that they have the ability tocause pri m a ry ke ratin disease, but theyh ave the ability to grow well on ke rat i n .

Tri ch o d e rma re a d i ly degrades cellu-lose and will grow on other fungi. Mucoris found in horse dung, l e ather pro d u c t s ,animal hair and jute. A s p e rgillus glaucusis a common outdoor fungus in thewinter and can be found growing onl e at h e r, grain and wool. Gliocladium iss t ru c t u ra l ly similar to penicillin.

We hy p o t h e s i ze that mech a n i c a ls t ress cre ated by ex c e s s ive toe length,l a m i n i t i s , poor management or injuryp redispose horses to the collection ofe nv i ronmental contaminants within thes t ratum medium. All of the identifi e df u n gi are env i ronmental organisms andcan be cultured from soil and wo o d.

The inner env i ronment of the strat u mmedium (chemical composition, ox y ge ntension and the limited ava i l ability ofm i c robial substrates) selects for speciesof fungi that can surv ive and grow we l lon ke rat i n .

Closing StatementThe goal of this study was to find a

valid method to asep t i c a l ly collect andc u l t u re mat e rial from cases of hoof wa l ls ep a ration. The results support a pri m a ryo ny ch o mycosis as the causat ive factor inhoof wall sep a rat i o n .

Once it was determined that fungi wa sthe sole infe c t ive factor invo l ve d, Il o o ked to find a potent yet safe antifunga lfor use in the tre atment. A solution ofch l o rine dioxide at 20,000 parts permillion proved to be an excellent ch o i c e.

This potent disinfectant used on ap ro p e rly prep a red hoof eliminated thep resence of fungal spores. I have hadp o s i t ive results using this chemical ont h ru s h , c a n ke r, s c rat ches and ra i n ro t .C h l o rine dioxide at 20,000 ppm is acti-vated using 1 deciliter ch l o rine diox i d e,1 deciliter of vinegar with 4 liters of wat e rfor a safe effe c t ive method of tre at i n gf u n gal infections of the hors e ’s hoof.

This study does not include a largenumber of cases, but the results we reve ry consistent. It is my hope to continu ebuilding on this fo u n d ation by culturi n gm o re cases. The most exciting part ab o u tthis study was finding a safe and effe c-t ive tre atment method for fungal infe c-tions of the horses hoof.

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TRAPPING GASES. The use of an IVbag or an inner tube to while soakingthe hoof in a chlorine dioxide solu-tion allows gases from the solution toattack fungal sprores.

HOOF CAST. If a shoe cannot be used to protect the hoof during treatment, a hoofcast can be another option.

r