severe hoof disease in free-ranging roosevelt elk (cervus ...severe hoof disease in free-ranging...

SEVERE HOOF DISEASE IN FREE-RANGING ROOSEVELT ELK

(CERVUS ELAPHUS ROOSEVELTI ) IN SOUTHWESTERN

WASHINGTON, USA

Sushan Han1,3,4 and Kristin G. Mansfield2

1 Washington Animal Disease and Diagnostic Laboratory, Washington State University, Pullman, Washington 99164-7034, USA2 Washington Department of Fish and Wildlife, 2315 N Discovery Pl., Spokane Valley, Washington 99216-1566, USA3 Current address: Diagnostic Medicine Center, College of Veterinary Medicine and Biomedical Sciences, Colorado StateUniversity, 1644 Campus Delivery, Fort Collins, Colorado 80523-1644, USA4 Corresponding author (email: [email protected])

ABSTRACT: Reports of free-ranging Roosevelt elk (Cervus elaphus roosevelti) with abnormalhooves and lameness increased significantly in southwestern Washington, USA, during winter2008. In March 2009 we examined five severely affected elk with clinical lameness from this regionto characterize hoof lesions, examine the general health of affected elk, and potentially identifyetiologies causing hoof disease. Three clinically normal elk from an adjacent but unaffected regionwere also collected as normal controls. Grossly, affected elk had deformed hooves that wereasymmetrical, markedly elongated, and curved or broken, as well as hooves with sloughed horn.Most affected elk had severe sole ulcers with extensive laminar necrosis and pedal osteomyelitis.Histopathology of normal and abnormal hooves identified acute and chronic laminitis in allaffected elk and one control elk. Hepatic copper and selenium levels in all affected and control elkwere also deficient, and hoof keratin copper levels were low. No significant underlying systemic ormusculoskeletal disease was detected in the affected elk, and attempts to isolate bacterial and viralpathogens were unsuccessful. A primary cause of hoof deformity was not definitively identified inthis chronically affected group. Studies to identify infectious hoof disease and to characterize acuteand subacute lesions are underway.

Key words: Cervus elaphus roosevelti, copper deficiency, elk, hoof disease, lameness,laminitis, selenium deficiency, sole ulcer.

INTRODUCTION

Hoof disease in wild and captive cervidshas been described worldwide, and etiologiesinclude infectious diseases such as epizootichemorrhagic disease and infectious pododer-matitis (Sleeman et al. 2009; Handeland et al.2010), noninfectious diseases such as mineraldeficiencies and endophyte toxicity (Flynnet al. 1977; Handeland and Vikren 2005), andchronic laminitis (Gray et al. 2001; Clauss etal. 2009), which is generally related tonutritional imbalance. In many cases, hoofdisease in wild cervids may be multifactorialand influenced by diet, behavior, habitat use,range quality, and population genetics (Lavinet al. 2004).

Sporadic reports of free-ranging deer, elk,and moose with hoof or leg abnormalities andlameness are received yearly throughoutWashington. The majority of reports areisolated cases for which a variety of causes arediagnosed (Washington Department of Fish

and Wildlife [WDFW] unpubl. data). Duringthe winter of 2008, reports of free-rangingRoosevelt elk (Cervus elaphus roosevelti)with abnormal hooves and lameness in-creased significantly in southwestern (SW)Washington, and reports have continued toincrease in geographic distribution sincethat time (WDFW unpubl. data). Weundertook an investigation in March of2009 to characterize hoof lesions, identifypossible etiologies, and evaluate elk forunderlying diseases. Five clinically lame elkwith abnormal hooves were euthanized andexamined. Affected elk were from herdswithin the Cowlitz River Basin region ofSW Washington, an area from which themajority of hoof disease had been reported.Additionally, three clinically normal elkfrom a nonaffected herd outside of thisstudy area were euthanized and examined.Here we provide clinical and pathologicfindings and characterize chronic hoof

DOI: 10.7589/2013-07-163 Journal of Wildlife Diseases, 50(2), 2014, pp. 259–270# Wildlife Disease Association 2014

259

disease in a population of free-rangingRoosevelt elk of SW Washington.

MATERIALS AND METHODS

Study area

Elk were collected in March 2009 on privatelands in SW Washington. The study areaextended from Chehalis, Washington (46u39943.920N, 122u57946.080W) on the northernborder to Longview, Washington (46u8917.880N, 122u56912.840W) on the southernborder, including areas both west and east ofInterstate Highway 5 (Fig. 1). The study sitewas comprised of a mixture of cultivatedpasture, shared by domestic cattle (Bostaurus), sheep (Ovis aries), and horses (Equusferus caballus), interspersed with large regionsof native lowland maritime coniferous forestand managed timberlands composed of Dou-glas fir (Pseudotsuga menziesii), westernhemlock (Tsuga heterophylla), and wes-tern redcedar (Thuja plicata) (Franklin andDyrness 1973).

Necropsy

Five adult female elk with visible hoofabnormalities and lameness from within thestudy area (study elk) and three adult female

elk with grossly normal hooves from outside ofthe study area (control elk) were killed viagunshot and immediately necropsied in thefield. Field necropsies were performed oneach elk (Table 1) and the following freshspecimens were collected sterilely and main-tained chilled on wet ice until processing inthe laboratory: lung, liver, kidney, spleen,mesenteric lymph node, ileum, coronary band,feces, serum, whole blood, and all four distallimbs removed at the level of the carpus ortarsus. Representative specimens of all viscerawere collected for histopathology and pre-served at least 24 hr in 10% neutral-bufferedformalin prior to processing. In pregnant elk,the fetus was necropsied and representativetissues including distal limbs were collected,with fresh and formalin-preserved tissueshandled similarly to those of the adults. Anupper canine tooth was removed from eachadult elk for aging via cementum annulianalysis (Matson’s Lab LLC, Milltown, Mon-tana, USA) (Hamlin et al. 2000). Freshspecimens were processed at either WyomingState Veterinary Laboratory (Laramie, Wyo-ming, USA), Washington Animal Disease andDiagnostic Laboratory (WADDL, Pullman,Washington, USA), or Colorado State Univer-sity Diagnostic Medicine Center (CSUDMC,Fort Collins, Colorado, USA).

FIGURE 1. Cowlitz River Basin, Washington State, USA, study area with the euthanasia location of fiveRoosevelt elk (Cervus elaphus roosevelti) with hoof lesions noted by asterisks (*). Affected elk representedthree herds with several affected cohorts in each. The capture locations of three grossly normal Rooseveltcontrol elk are noted by squares (&). Control elk were from a nonaffected herd immediately east of thestudy area.

260 JOURNAL OF WILDLIFE DISEASES, VOL. 50, NO. 2, APRIL 2014

Radiology and histopathology

Paired abnormal limbs from three study elkand paired normal limbs from two control elkwere radiographed at Washington State Uni-versity Veterinary Teaching Hospital. Digitalimages of anterior-posterior and lateral viewswere obtained and were interpreted by aboard-certified veterinary radiologist.

Histopathology was performed at WADDLon all formalin-fixed tissues by routine meth-ods (Lillie 1965). Each hoof was sagittallysectioned toe to heel on a commercial bandsaw to an approximate thickness of 5 mm andfixed in 10% neutral buffered formalin for 24–48 hr. Formalin-fixed sections were thendecalcified in a solution of 5% formic acidand 37% formalin (Spencer and Bancroft1980) for 24–48 hr. Sections were then deke-ratinized using a paste solution of potassiumthioglycolate, calcium hydroxide, and sodiumhydroxide (NairH, Nair Industries, Marietta,Georgia, USA). Sections were packed in pasteand wrapped with plastic film until keratin waspliable (approximately 3 wk), routinely remov-ing and replacing the paste every 4 days(Bancroft and Gamble 1980, with modifica-tions). Once pliable, sections were paraffinembedded, sectioned 7–10 mm, and stainedwith hematoxylin and eosin for microscopicexamination. Replicate sections of slides wereGram stained with Brown and Hopp’s as

described (Luna 1968) and silver stained forspirochete bacteria (Steiner’s) and fungi (Gro-cott’s methenamine silver) (Crookham andDapson 1991). All prepared slides wereexamined by light microscopy by two board-certified anatomic pathologists who wereblinded to the gross findings.

Laboratory testing

Virus isolation: For each elk, fresh lung, liver,spleen, kidney, mesenteric lymph node, ileum,and coronary band were pooled, and for eachfetus, fresh liver, spleen, kidney, and hooves werepooled. Tissue pools were chilled on wet ice forapproximately 48 hr before arrival in thelaboratory. Once in the laboratory, specimenswere chilled at 4 C and cultured for virus isolation(Wyoming State Veterinary Laboratory). Tissuecultures included bovine embryonic testicle(Schmidt and Lenneth 1964), white-tailed deer(Odocoileus virginianus) umbilical endothelialcells (Howerth and Stallknecht 1995), andcommercially available bovine cardiopulmonaryarterial endothelium (CPAE, No. CCL 209,ATCC, Rockville, Maryland, USA), using meth-ods for each culture as previously described.

Serology: Whole blood was collected fromthe heart, aorta, or vena cava at necropsy.Serum was separated, stored at 220 C, andlater thawed for analysis of antibody titers to

TABLE 1. Summary of gross lesions from affected study site Roosevelt elk (Cervus elaphus roosevelti) andnormal control elk harvested from southwestern Washington. Measurements of hooves (cm) provided for eachlimb and significant visceral lesions.

ElkNo.

Age(yr)

Status andorigina

Left fore Right fore Left hind Right hind

Other grosslesions

Medial(cm)

Lateral(cm)

Medial(cm)

Lateral(cm)

Medial(cm)

Lateral(cm)

Medial(cm)

Lateral(cm)

1 3 NP/NL,study site

8.2b 10.5 9.9 7.8b 9.0 9.1 9.4 9.0 Pulmonary abscesses,lung worms, left frontvalgus deformity

2 4 NP/L,study site

10.6 10.4 10.5 10.3 5.5c 14.5 19.6d 15.5 Lung worms, serousatrophy of marrow

3 5 P/NL,study site

9.5 9.0 10.0 9.3 14.0d 15.0 8.8 8.4 Serous atrophyof marrow

4 7 P/L, control 9.3 9.3 9.4 9.5 9.5 9.3 9.4 9.6 None5 2 P/NL, control 8.6 8.6 8.4 8.8 8.5 8.6 8.8 8.6 None6 5 NP/NL, control 8.9 9.1 8.5 8.4 8.5 8.5 8.4 8.4 None7 ,1 NP/NL,

study site9.9 11.1 9.4 9.0 11.6d 9.2 6.4b 11.6d None

8 2 NP/NL,study site

8.5d 8.7 10.2 9.5 9.2 8.5 8.1 8.0 None

a NP 5 nonpregnant; NL 5 nonlactating; L 5 lactating; P 5 pregnant.b Sloughed hoof wall.c Broken hoof.d Sole ulcer.

HAN AND MANSFIELD—HOOF DISEASE IN WILD ROOSEVELT ELK 261

viruses known to be associated with vasculardisease and hoof or coronary band lesions atWADDL. Specifically, antibodies to epizootichemorrhagic disease viruses (EHDVs) weremeasured by agarose gel immunodiffusionassay (Pearson and Jochim 1979) and antibod-ies to bluetongue virus (BTV) were measuredby a competitive enzyme-linked immunosor-bent assay commercially available kit (Veteri-nary Medical Research and Development,Pullman, Washington, USA) performed perthe manufacturer’s instructions. A cutoffinhibition value of 50% was used to determinepositive results. Bovine viral diarrhea virus(BVDV) type I was analyzed by virus neutral-ization (Hill 1977).

Parasitology: Feces were collected at necrop-sy and stored at 4 C until processed andexamined for intestinal parasite ova using theWisconsin sugar flotation method, lung wormlarvae (Dictyocaulus sp.) using the Baermanntechnique (Baermann 1917), and liver flukeova (Fasciola sp. or Fascioloides sp.) usingsedimentation (Zajac and Conboy 2006).Sample preparation and light microscopy wereoverseen by a parasitologist at WADDL.

Bacteriology: Fresh sections of coronary band,hoof wall, heel bulb, and full-thickness skinfrom the interdigital space were pooled forindividual elk, chilled at 4 C, and cultured bystreaking on trypticase soy agar with 5% sheepblood agar plates, MacConkey’s agar plates,and Columbia blood agar for aerobic cultureand anaerobic blood agar plates for anaerobes.Hoof wall lesions from each elk were culturedsimilarly, but separately. Aerobic plates wereincubated 48–72 hr under atmospheric condi-tions at 37 C, and Columbia blood agar wasincubated similarly under 5% CO2. Anaerobicplates were cultured under anaerobic condi-tions at 37 C. Anaerobic culture isolates weresequenced by PCR using 16s rDNA primers(Drancourt et al. 2000) and the speciesidentified. All samples were processed atWADDL.

Hepatic trace mineral analysis: Five grams offresh liver was collected from each elk, chilledat 4 C, and analyzed for copper, selenium,cobalt, zinc, manganese, and molybdenumlevels by inductively coupled plasma massspectrometry (Anderson 1996) at WADDL.Results were reported on a wet weight basisand compared to values reported for cattle(Kincaid 1999), California tule elk (Cervuscanadensis nannodes; Johnson et al. 2007), andRocky Mountain elk (Cervus elaphus nelsoni;Zaugg and Kinsel 1997).

Hoof keratin copper analysis: One normal andone abnormal hoof from each of three studyelk and two normal hooves from each of twocontrol elk were selected for analysis. Approx-imately 1 cm3 of keratin from the dorsal hoofwall was collected 2 cm distal to the coronaryband. Hoof wall samples were frozen at 220 Cuntil analysis at CSUDMC. Analysis wasperformed by digestion of the hoof specimenand flame atomic absorption spectroscopy aspreviously described for analysis of hair, withsome modifications (Helrich 1990). Briefly,fresh hoof wall without lamina was washed andapproximately 1 g of hoof was dried, ashed at600 C, and dissolved in 10 mL of 3.6 N HNO3

for spectroscopy. Results were compared tovalues reported for free-ranging Alaskanmoose (Alces alces gigas; Flynn et al. 1977)and domestic cattle (Hidiroglou and Williams1986; Sugg et al. 1996).

RESULTS

Necropsy

Gross hoof lesions and ancillary viscerallesions are summarized in Table 1. Elkhad a spectrum of gross hoof lesions,which occurred in medial or lateral hoovesof affected limbs, and paired forelimbsand hindlimbs, but rarely involved bothforelimbs and hindlimbs concurrently.Hoof lesions included overgrowth of thehoof wall and elongation of the toe (5/5elk) that varied from moderate (11.1 cm;Fig. 2B) to severe (19.6 cm) with twistingdeformation (Fig. 2C, D); complete sloug-hage of the hoof wall (3/5 elk; Fig. 2C, D)with secondary osteomyelitis and septicarthritis (2/5); hoof wall defects includingulcers, horizontal ridges, and vertical clefts(3/5 elk); full-thickness sole ulcers withlaminar necrosis and osteomyelitis of P3 (4/5 elk; Fig. 3A–D); and heel bulb ulcerationand hyperplasia (3/5 elk; Fig. 2E). Threecontrol elk had no gross hoof lesions(Fig. 2A). Significant gross visceral lesionswere detected only in study elk and includedserous atrophy of bone marrow fat andgeneralized emaciation (2/5 elk); mild pul-monary nematodiasis (Dictyocaulus sp.; 2/5elk); and small pulmonary abscesses (1/5 elk).Gross visceral lesions and emaciation werenot detected in control elk.


Radiology and histopathology

Hoof and fetlock radiographs of threestudy elk were performed, and findingsincluded P3 osteomyelitis in sloughed,broken, and ulcerated hooves (2/3 elk;Fig. 4A) with septic arthritis of the distalinterphalangeal joint (1/3 elk) and mildpedal osteitis of intact elongated hooves(2/3 elk; Fig. 4B, C). No bone abnormal-ities were noted in two radiographedcontrol elk.

Detailed histologic examination wasperformed on all study and control elk,including full-sagittal sections of hooves;incisional biopsies of the coronary band,interdigital space, and heel bulb; andrepresentative incisional biopsies of allviscera. Histologic findings in the limbsof the study elk were moderate to severe

lymphoplasmacytic perivasculitis of thehoof lamina (Fig. 5B; 5/5 elk) and of thedermis of the heel bulb and coronary band(5/5 elk); suppurative, necrotizing lamini-tis with vasculitis and arteriolar thrombosis(Fig. 5C) in broken, sloughed, and ulcer-ated hooves (5/5 elk); mild to severechronic hypertrophic arteriosclerosis withvacuolar degeneration of the tunica mediaand adventitial fibrosis (Fig. 5D; 5/5 elk);and normal parallel keratin tubules of thehoof wall and sole (5/5 elk). Histologicfindings in the limbs of control elkincluded moderate laminar perivasculitisand arteriosclerosis (1/3 elk) and nohistologic hoof lesions (Fig. 5A; 2/3 elk).Special stains (GMS, Gram, Steiner’s) ofsagittal sections of study elk hooves,coronary band, interdigital space, and heel

FIGURE 2. Hooves from clinically normal and clinically lame Roosevelt elk (Cervus elaphus roosevelti).(A) Hooves from clinically normal control elk 5. (B) Forelimbs from lame study elk 8, which had moderateovergrowth and scissoring of the hooves and clinical lameness. (C) Hindlimbs from lame study elk 7 withsevere overgrowth and deformity of the hooves, sloughing of the hoof wall at the coronet band (asterisk), anddissecting laminitis from necrotizing sole ulceration (arrowhead). (D) Forelimbs from lame study elk 1 withsevere overgrowth of hooves and sloughed (asterisk) and broken hooves (arrow). (E) Palmar surface of theforelimbs from lame study elk 1 showing hyperkeratosis and ulceration of the heel bulbs. Numbers on rule atleft are at 10-mm intervals.


FIGURE 3. Gross photographs of sole ulcers from clinically lame Roosevelt elk (Cervus elaphus roosevelti)euthanized in the study area. (A) Plantar surface of the right hind lateral hoof from lame study elk 7 showingsevere sole ulceration and marked overgrowth and scissoring of the hooves bilaterally. (B) Sagittal crosssection of the right hind lateral hoof from lame study elk 7 (image A) showing severe sole ulceration anddiffuse laminar necrosis with osteomyelitis of the third phalanx (P3) and granulation tissue (asterisk).(C) Dorsal surface of the left forelimb from lame study elk 8 showing moderate overgrowth of the hooves, butgrossly normal hoof walls. (D) Palmar surface of the same left forelimb (image C) shows severe sole ulcerationand laminar necrosis with extensive granulation tissue surrounding P3.

FIGURE 4. Anterior-posterior radiographs of three clinically lame Roosevelt elk (Cervus elaphusroosevelti) from the study site. (A) Forelimbs from elk 1 showing osteomyelitis and interphalangealosteoarthritis associated with broken and sloughed hooves, but minimal bony changes on intact hooves despitesevere overgrowth of the hoof wall. (B) Forelimbs from lame elk 8 showing minimal bony changes butosteomyelitis of the third phalanx (P3) of the left front medial toe (arrowhead) associated with sole ulceration.(C) Left hindlimb from elk 3 with markedly overgrown hooves and minimal bony lesions but osteomyelitis ofP3 of the medial hoof (arrowhead) associated with a sole ulcer.


bulb showed only a superficial mixture ofgram-negative and -positive noninvasivebacteria, which was often not directlyassociated with inflammation.

Histologic examination of viscera showedseveral minor spontaneous lesions instudy and control elk. Lesions includedmoderate hepatic portal and bridgingfibrosis (3/8 elk); mild lymphocytic peri-vasculitis of the meninges, brain, heart, orgastrointestinal tract (4/8 elk); mild non-suppurative myocardial degeneration (1/8elk); mild glomerulonephritis (1/8 elk);mild lymphoplasmacytic renal interstitialnephritis (4/8 elk); chronic small abscess-es in the lungs, tongue, or kidney (3/8elk); and moderate numbers of skeletal

muscle sarcocysts (Sarcocystis sp.) notassociated with inflammation (8/8 elk).

Laboratory testing

Virus isolation from fresh tissues of allstudy and control elk and three fetuseswas negative, and no elk had detectableantibody to EHDV, BTV, or BVDV type I.Parasitologic examination of fresh fecesfrom four study elk and two control elkwas performed. All elk had low numbersof some or all of the following parasites:Dictyocaulus sp., Trichuris sp., Capillariasp., Strongylus sp., and coccidia. Bacterialculture of the interdigital space, coronaryband, heel bulb, and hoof lesions fromfour study elk and two control elk yielded

FIGURE 5. Photomicrographs of hooves from Roosevelt elk (Cervus elaphus roosevelti) that were clinicallynormal or lame. (A) Normal lamina (white arrowhead), laminar epithelium (white asterisk), and hoof wall(white arrow) from a clinically and grossly normal control elk 5. H&E stain. 403. Bar5500 mm. (B) Markedlymphoplasmacytic laminar perivasculitis (black arrowheads) from lame study elk 1. Similar chronic lesionsare noted in all five study elk and one clinically normal control elk. H&E stain. 1003. Bar5100 mm.(C) Suppurative laminar vasculitis and thrombosis (black asterisks) from lame study elk 2 consistent with acutenecrotizing laminitis in association with a broken hoof. Similar lesions are noted in three of five study elk andno control elk. H&E stain. 2003. Bar525 mm. (D) Chronic arteriosclerosis of laminar blood vessels (blackarrows) from lame study elk 3. Note intimal hypertrophy, medial smooth muscle proliferation and vacuolardegeneration, and extensive fibrosis of the tunica adventitia. Similar lesions are noted in all five study elk andone control elk. H&E stain. 1003. Bar5100 mm.


mixed aerobic and anaerobic culturesconsistent with overgrowth of contami-nants. Anaerobic cultures grew coloniesthat were identified by 16s rDNA PCRand sequencing as opportunistic environ-mental pathogens Helcococcus ovis andAnaerovorax sp. (2/4 study elk). Hepatictrace mineral concentrations (Table 2)showed copper deficiency in study elk (4/5 elk, range 3.1–9.6 mg/g), and control elk(3/3 elk, range 2.5–6.0 mg/g), as well asselenium deficiency in study elk (5/5 elk,range 0.056–0.41 mg/g) and control elk (3/3 elk, range 0.11–0.12 mg/g). Hepaticcobalt was elevated in study elk (3/5 elk,range 0.091–0.12 mg/g) but normal incontrol elk (3/3 elk). No elevated ordeficient levels of hepatic zinc, manga-nese, molybdenum, chromium, nickel,arsenic, cadmium, or lead were detectedin any of the study or control elk (Table 2).Copper levels of hoof keratin were deter-mined for three study elk and two controlelk (Table 2). In study elk, both abnormaland normal hooves from each animal wereexamined and keratin copper levelsranged from 0.87 to 3.15 parts per milliondry weight, similar to copper levels innormal hooves from control elk.

DISCUSSION

Hoof disease in herds of free-rangingRoosevelt elk has been a growing concernin SW Washington in the last 4 yr, with thenumber of affected elk and distribution ofaffected herds steadily increasing. Afterdetailed gross and histologic evaluation offive affected elk from the Cowlitz RiverBasin study area, no underlying systemicor bone related disease was detected,indicating hoof disease is likely a primarylesion. Elk had moderately (10 cm) toseverely (19.6 cm) elongated and de-formed hooves with histologically normalhorn. Accelerated hoof growth, resulting inabnormally long hooves, has been welldescribed in wild and domestic ruminantsand is associated with chronic hoof inflam-mation from various causes, including

chronic laminitis (Boosman et al. 1991;Singh et al. 1992; Gray et al. 2001) andinfection with contagious hoof diseasebacteria (Handeland et al. 2010). Hoofelongation can be exacerbated by disusefrom pain and lack of normal mobility andwear. Most study elk had severe sole ulcersat the heel-sole junction with laminarnecrosis in at least one hoof. Sole ulcersoccurred in severely elongated hooves aswell as relatively normal-length hooves,which may indicate that ulceration is aprimary lesion with secondary horn over-growth accelerated by chronic inflamma-tion and lack of weight bearing. Sole ulcersare common sequelae to chronic laminitisin domestic ruminants and are thought tobe due to vascular compromise of thecorium, leading to laxity in the suspensoryapparatus of P3 and compressive damageof the digital pad and sole by P3. Concur-rently, chronic inflammation results inproduction of weak hoof wall and solekeratin, which can culminate in ulcerationof the sole at the heel-sole junction(Lischer and Ossent 2001; van Amsteland Shearer 2006). Three study elk hadsloughed or broken hooves with scarringof the coronary bands and necrosis of thedermal corium. Sloughing of the hoof wallin ruminants is most commonly associatedwith severe laminitis, where prolongedvascular compromise leads to laminarnecrosis and shearing and detachmentof the dermal corium and hoof wall(Thoefner et al. 2005). This may havebeen exacerbated by mechanical torquecaused by extraordinarily long hooves.Histologically, all study elk and onecontrol elk had prominent laminar peri-vascular inflammation and hypertrophicarteriosclerosis with thrombosis, lesionsclassically described in chronic laminitisof domestic ruminants. These lesionsindicate that hoof deformity is at leastultimately associated with chronic lamini-tis. Unfortunately, it is unclear whetherlaminitis is the primary cause of hoofdisease or secondary to chronic hoofdeformity and inflammation.


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96

).


Study elk had limited soft tissue lesionsinvolving the interdigital skin, heel bulb,and coronary band, including those withseverely deformed hooves. These regionsare key sites for both early and advancedinfectious hoof disease lesions as de-scribed in many species of domestic andnondomestic ruminants (Wani and Sa-manta 2005; Belloy et al. 2007; Bennettet al. 2009; Evans et al. 2009). Though softtissue lesions were not consistently detect-ed, the five study elk had chronic disease,and earlier lesions may have been nolonger apparent. Importantly, infectioushoof diseases that are well described indomestic animals may present differentlyin this nondomestic species. We per-formed aerobic and anaerobic bacterialculture of hoof lesions and soft tissues, andno pathogenic bacteria or fungi wereisolated. However, the interval of tissuecollection in the field and processing inthe laboratory was prolonged and subop-timal for important fastidious aerobes andspirochetes such as Dichelobacter nodo-sus, Fusobacterium necrophorum, andTreponema sp., respectively. Additionally,these organisms, even under optimalconditions, require specialized growthmedia and conditions that were notutilized in this study. Attempts to evaluateyounger animals with more acute lesionsare underway, and fresh tissues are beingcollected into appropriate medium andrefrigeration in the field for optimalculture and PCR.

Virus isolation and serology of study elkdid not identify an underlying viral etiol-ogy and showed lack of serum antibodyand, therefore, exposure to viruses thatcould potentially cause vascular and hoof-related disease, specifically BTV, EHDV,and BVDV I. Mineral analysis of livershowed that all elk were generally seleni-um deficient and all but one study elkwere copper deficient (Hidiroglou andWilliams 1986; Zaugg and Kinsel 1997;Johnson et al. 2007). Copper levels in hoofwall of all elk were below limits previouslyestablished for wild Alaskan moose (Flynn

et al. 1977) and domestic cattle (Sugg et al.1996). Copper is a vital component ofkeratin, and deficiency may lead toabnormal sulfur cross-linking, resulting indefective hoof keratin, but generally alsodefective antlers and hair coat (Goganet al. 1989; Johnson et al. 2007), which wasnot identified in this study or in affectedelk in this region in general. Copperdeficiency in cattle is associated withincreased incidence of infectious hoofdisease, heel cracks, and sole ulcersthought to be due to weak, fragile hoofand sole keratin (Tomlinson et al. 2004). Apopulation of Alaskan moose was de-scribed with lameness and severe over-growth of the hooves (Flynn et al. 1977),and the cause of this lesion, called ‘‘slipperfoot,’’ was speculated to be copper defi-ciency. The role of dietary copper defi-ciency in hoof deformity, laminitis, andsole ulcers in the Cowlitz River BasinRoosevelt elk has not been determined,though elk in this region have historicallycohabited with low dietary selenium andcopper without previous outbreaks of hoofdisease. Studies in moose and domesticcattle, however, would suggest copperdeficiency may be an important predis-posing factor, or at least an additionalcomplication, to hoof disease in thispopulation. Future studies will continueto elucidate the role of copper in thisdisease process, as well as to examine thebiotin status of these elk. Biotin is animportant component of normal hoof,skin, and hair development in mostspecies and is associated with degenerativeand necrotic hoof disease in states ofdeficiency, particularly reported in swine(Misir and Blair 1986).

Much remains to be learned about theinfluence of environmental factors on hoofdisease in these wild elk. Factors ofinterest include forage contamination withtoxic endophytes, specifically ergot andfescue toxicity, the latter of which wasanecdotally described in domestic cattle inthis region in the 1980s (C. Gay unpubl.).Endophytic toxins are capable of causing


digital vascular compromise leading tolaminitis and distal gangrenous devitaliza-tion of the hooves and limbs (Handelandand Vikøren 2005). Diagnosis of toxicendophytes requires detailed range stud-ies, which will be incorporated in futureprojects. Additionally, basic understandingof herd dynamics in affected regions will beessential, including knowledge of foragingbehavior, nutrition, daily movements, mi-gration, habitat usage, and interaction withdomestic livestock. As SW Washington is avery wet maritime habitat, the roles ofhumidity and climate change also need tobe considered. The winter of 2007–2008,when cases of hoof disease were first noted,was a historically wet year with remarkablerainfall and areas of flooding, which mayhave concentrated both wildlife and do-mestic livestock, allowing for transmissionof contagious hoof diseases. Importantly,no hoof disease has been reported indomestic livestock by area veterinariansand landowners.

In conclusion, adult Roosevelt elk inSW Washington with chronic and severelameness had severely overgrown anddeformed hooves with sole ulcers andsloughed hoof walls. Study elk and onecontrol elk had laminar vascular lesionsconsistent with chronic laminitis. Affectedand control elk were copper and seleniumdeficient. Initial screening did not identifyan underlying viral or infectious bacterialpathogen. However, an infectious etiologyseems plausible to explain rapid andcontinued spread of hoof disease. Studiesto identify and characterize acute hooflesions and to optimize conditions forbacterial isolation are necessary and un-derway. Investigation of habitat use, prin-cipal diet, and behavior may be necessaryto completely understand the dynamicsand influence of these factors on thepathogenesis of hoof disease in thispopulation of free-ranging Roosevelt elk.

ACKNOWLEDGMENTS

A special thank you to Gary J. Haldorsonand the late Lindsay Oaks at Washington

Animal Disease and Diagnostic Laboratory(WADDL) for additional review of histopatholo-gy and bacteriology, respectively; Pat Miller,Annemarie Prince, Ella Rowan, Eric Holman,Scott Shroeder, and Ted Holden of WashingtonDepartment of Fish and Wildlife for fieldassistance and sample handling; Tom Besserand Dan Bradway from WADDL for bacterialPCR; Patricia Talcott from WADDL andDwayne Hamar from Colorado State UniversityVeterinary Diagnostic Laboratory for hepatictrace element and heavy metal levels and hoofcopper analysis, respectively; Michael Garner(Northwest Zoopath); Richard Whittington (Uni-versity of Sydney, Australia), and Steve Parish(Washington State University College of Veteri-nary Medicine) for consult and valued opinions;and Jay Oaks for technical assistance with figures.This research was funded by the WashingtonDepartment of Fish and Wildlife with minorcontributions from Colorado State UniversityDiagnostic Medicine Center.

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Submitted for publication 12 July 2013.Accepted 9 October 2013.


severe hoof disease in free-ranging roosevelt elk (cervus ...severe hoof disease in free-ranging...

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