SPONTANEOUS PASTEURELLOSIS IN CAPTIVE ROCKY MOUNTAIN BIGHORN SHEEP (OVIS CANADENSIS CANADENSIS): CLINICAL, LABORATORY, AND EPIZOOTIOLOGICAL OBSERVATIONS Author(s): Michael W. Miller, N. Thompson Hobbs, and Elizabeth S. Williams Source: Journal of Wildlife Diseases, 27(4):534-542. Published By: Wildlife Disease Association DOI: http://dx.doi.org/10.7589/0090-3558-27.4.534 URL: http://www.bioone.org/doi/full/10.7589/0090-3558-27.4.534

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of Wildlife

Journal

Diseases, C Wildlife

SPONTANEOUS BIGHORN

PASTEURELLOSIS

(OVIS

SHEEP

LABORATORY, Michael

AND

W. Miller,2

IN CAPTIVE

CANADENSIS

CANADENSIS):

EPIZOOTIOLOGICAL

N. Thompson

Hobbs,3

ROCKY

27(4),

pp. 534-542

1991,

Disease

Association

1991

MOUNTAIN CLINICAL,

OBSERVATIONS

and Elizabeth

S. Williams4

‘Department of Rshery and Wildlife Biology, Colorado State University, Fort Collins, Colorado 80523, USA 2Present address: 3Colorado Division of Wildlife, Wildlife Research Center, 317 West Prospect Road, Fort Collins,

Colorado 80526, USA of Veterinary Sciences, Wyoming State Veterinary 1174 Snowy Range Road, Laramie, Wyoming 82070, USA

ABSTRACT: We observed clinical tests on 12 captive Rocky Mountain taneous outbreak of pasteurellosis.

signs,

compared

Laboratory,

University

of Wyoming,

responses, and performed diagnostic canadensis canadensis) during a sponCortisol in urine and feces was measured for bighorns sampled three times between 20 October and 1 November 1986. By 6 November, four of these had developed pneumonia, four showed only mild rhinitis, and four remained clinically normal. Bighorns that ultimately developed pneumonia showed elevated mean urinary (P = 0.003) and fecal (P = 0.046) cortisol excretion over the 12-day sampling period. Twenty-four hour mean urine cortisol : creatinine ratios ranged from 10 to 57 ng/mg dry matter for affected and 5 to 22 ng/mg for healthy individuals; 24 hr mean fecal cortisol concentrations ranged from 7.2 to 20 ng/g dry matter for affected and 3.6 to 9.1 ng/g dry matter for healthy individuals. Elevated cortisol excretion preceded clinical pneumonia in affected bighorns by 16 days. Beta-hemolytic Pasteurella haemolytlca biotype T, serotype 3 or 4, was isolated from nasal and pharyngeal swabs from all eight bighorns with pneumonia or mild rhinitis. We detected no evidence of parainfluenza 3, bovine respiratory syncytial virus, or Chiamydia psittaci using fluorescent antibody and/or serologic tests. Although elevated cortisol excretion was associated with pneumonia, we also believe age, reproductive physiology, and/or prior recovery from clinical pasteurellosis may have influenced individual susceptibility to pneumonia during this epizootic. Key words: Rocky Mountain bighorn sheep, Ovis canadensis canadensis, pneumonia, cortisol, stress, epizootiology, pasteurellosis, Pasteurella haemolytlca. bighorn

adrenal

sheep

INTRODUCTION Chronic predispose sis)

to

pneumonia

(Hudson,

et a!.,

1980;

1982;

Onderka

and

et a!.,

1984).

Anecdotal

monia Suggest

et al.,

Bailey,

1986;

Festa-Bianchet,

theory,

adrenal

responses

these

environmental

coid-mediated crease susceptibility diseases,

mortality

1984;

The

increase

observations stress may

suggests be associated

evidence that

1985; et re-

captive epizootic. and clini-

as diagnostic outbreak.

Colorado

Division

(CDOW) Wildlife Research West Prospect Road, Fort rado

circumstantial

et a!.,

find-

HISTORY

rates.

Although

not

by corti-

into infec-

thereby

(Hobbs

cal observations, as well ings, made during this

In

stimulated

immunosuppression, of bighorns

pneumonia

sponses of affected and unaffected bighorns during a pneumonia We also report epizootiological

1988). cause

data have

Harlow et al., 1987; Miller, 1988; Miller a!., 1991). Here, we describe adrenal

outbreaks et al.,

stressors

and

to induce

populations disturbances

Spraker

experimental

hypothesis

To the contrary, experimentallyimposed stress resulting in measurable adrenal responses in captive bighorns failed

of pneu-

disease

sheep,

this

emerged.

Spraker

accounts

1980;

to

Hibler,

1984;

in bighorn

supporting

1973;

and

Wishart,

precede

(Feuerstein

field mental

1972,

Spraker

outbreaks in bighorn that environmental

frequently

tious

monia

stress is one factor believed bighorn sheep (Ovis canaden-

Feuerstein

(Ovis

from

80526,

USA)

of captive Rocky (0. canadensis

environwith pneu-

purposes 534

since

has

Wildlife

Center Collins,

maintained

Mountain canadensis) 1977.

of

Most

(317 Coloa herd

bighorn sheep for research of

these

sheep

MILLER

have

been

adapted spread

hand-raised,

and

to captivity. through our

all appear

nia,

histologic of acute and

lung

examinations fibrinous

first during

Pasteurella

tissue.

developed ber, and

In

sp. all,

revealed bronchopneumowas

seven

isolated of

19

clinical pneumonia three of those (two

6-yr-old ewe) died. and prolonged oral acting oxytetracycline York,

bighorns a

Isolation procedures and injectable long(Liquamycin#{174}

Agricultural Division, York 10017, USA) therapy

New

le-

by Decemlambs and

New were

credited with halting this outbreak and saving four affected ewes (A82, C83, G78, T82) (Table 1). It is possible that Pasteurella sp. was introduced by one of eight bighorns that had been added to our herd within the previous year, but no samples were collected to screen to their introduction. Aside

from

new

animals

born ewes

Gross

lesions

third

lamb

nasal

discharge

with and Pasteurella lungs of both lambs. developed

afJuly. acute sp.

The in

from the Reto CDOW’s Facility (Fort

Collins, Colorado 80521, USA; 40#{176}35’N, 105#{176}10’W). That lamb recovered after a 3-wk course of injectable long-acting oxmonths,

therapy. no

other

(Table 1). In October our

foothills

cortisol concentrations feces for detecting ited

by

chronic

Over

bighorns

1986, facility

N(A)

N

P/Dd

CM

N (A)

N

P/R’

M86

M

-

-

P/R’

Q86

F

-

-

P/R’

A85

F

-

P/R

RH’

C83

F

P/R

RH

RH’

we

the were

initiated

to examine

next affected a study

at

utility

of

in bighorn urine adrenal responses adrenocorticotropic

12

and elichor-

1985

1986

D83

M

N

N

RH’

T82

F

P/R

RH

RH’

A82

F

P/R

N

N

E83

F

N

N

N

G78

F

P/R

N

N

H83

M

N

N

N

N,

normal;

rhinitis; Ear

N (A), P/R,

tag

(1977

1982

and

1986);

1985,

A82

and

(A-T) A85

RH,

pneumonia, are

died.

and

related,

year

of

born

in

Pasteurella

haemolytlca

pharyngeal

swabs.

biotype

T, serotype

P. haemolytica

biotype

T, serotype

4 isolated

P. haemolytica

biotype

T, serotype

3 isolated

swabs.

‘Unserotyped

a!.,

name/lineage

i.e.,

facility;

P/D,

swabs.

nasal

beta-hemolytic

from

mone

alternate

male.

‘Beta-hemolytic

lated

at

respectively.

from

nasal

held recovered;

indicate

to

castrated

from

normal,

pneumonia,

numbers

birth

3 isolated

in

pneumonia

September, after bighorns search Center were moved Foothills Wildlife Research

ytetracycline

CM’

G77

from

consistent

(A85)

B82

Beta-hemolytic

prior

in May 1985 to previously (C83, T82) died by late

bronchopneumonia, was isolated from

1984

‘Beta-hemolytic

occasional

were

$

conditionto October’

Sex

‘CM,

two ewes (C83, T82) and one ram, none of the adult bighorns showed respiratory signs after the outbreak subsided in December 1984. However, two of three dam-raised lambs fected

Clinical September

Ear tag numberb

from

LA200#{174}, Pfizer

535

1. Abbreviated health histories emphasizing prior pneumonia experience for 12 captive bighorns sampled during the 1986 pasteurellosis outbreak. See text for a more complete historical account.

October to December 1984. The index case for this epizootic was a dam-raised lamb that died suddenly in mid-October. Gross and sions

IN BIGHORNS

TABLE

well-

Pasteurellosis captive herd

ET AL.-PASTEURELLOSIS

nasal

(ACTH) 1991).

P. haernolytica

biotype

T iso-

swabs.

administration

Before

we

could

(Miller begin

experimental treatments, pneumonia veloped in four of 12 captive bighorns lected

for

that

study.

allowed an unusual ine relationships sponses sheep.

and

respiratory

MATERIALS Animals

This

opportunity between

et

imposing dese-

development to examadrenal re-

disease

in bighorn

AND METHODS

and housing

Twelve hand-raised bighorns (Table 1) had selected for use in the aforementioned experiment. On 13 October 1986, all 12 sheep entered individual isolation pens (about 50 m2), where they were housed before and between excreta collections (described below). During excreta collections, each bighorn was confined in an individual metabolic cage (about 5 m2). Pens and cages were arranged so that confined bighorns could see and contact each other, and

been

536

JOURNAL

all

sheep

OF WILDLIFE

were

peared

previously

acclimated

We provided and Hobbs, ad libitum. Clinical

DISEASES,

to

alfalfa

VOL. 27, NO. 4, OCTOBER

trained this

for

type

of

and

ap-

confinement.

hay, pelleted feed (Baker mineralized salt, and water

1985),

observations

Because

we detected upper respiratory signs (coughing, nasal discharge) in one bighorn just prior to beginning excreta collections, we began monitoring all penned sheep daily for clinical signs

and/or

progression

on 20 October.

of

In particular,

disease.

We

disease

we noted presence as well as changes in

and severity of coughing, nasal secretions or behavior ratory

respiratory

suggestive

classified

nasal

of

with

or without occasional coughing in the of depression and anorexia as rhinitis. pneumonia

was

distinguished

respi-

discharge

from

absence Clinical

rhinitis

by

a combination of signs including depression, anorexia, coughing, and mucopurulent nasal discharge. Bighorns that developed pneumonia were treated using about 22 mg/kg of longacting oxytetracycline (Liquamycin#{174} LA200#{174}, Pfizer York

ery

Agricultural

Division,

10017, USA) other day.

New

injected

York,

New

subcutaneously

ev-

Urine and fecal cortisol measurements We made

three

48 hr excreta

collections

from

bighorns on 21 to 22 October, 26 to 27 October, and 31 October to 1 November. Bighorns were confined in individual metabolic cages throughout each collection period. These cages were

constructed of galvanized steel with mesh flooring. A galvanized steel pan that narrowed into a funnel was overlayed with screening and placed beneath each cage floor to collect excreta. Feces were deposited on the screening, while urine passed through to the pan and drained into a 1-L separated

plastic bottle. This layering effectively feces from urine and minimized cross-

contamination

of

and

urine

feces

excreta

twice

samples.

daily,

and

We

collected

made

two

24

bighorn per sampling period. Urine samples were filtered immediately after collection. All samples were stored at -20 C until assayed. Cortisol was measured by an extracted double-antibody radioimmunoassay validated for use with bighorn urine and feces (Miller, 1988; Miller et al., 1991). Our methods for measuring urine and fecal cortisol and urine creatinine in bighorn samples followed those described by Miller et al. (1991). Cortisol assays were performed by the Endocrinology Laboratory, Department of Physiology, Colorado State Unihr

composites

versity

(Fort

Creatinine

ical

Pathology

for

each

Collins, assays

were

Laboratory,

Colorado

80523,

performed

Department

by

USA). the

Clin-

of Clin-

1991

ical Sciences, Colorado State University (Fort Collins, Colorado 80523, USA). We used urine cortisol:creatinine ratios (ng/mg) and fecal cortisol concentrations (ng/g dry matter feces) to compare cortisol levels in 24 hr composite samples. Diagnostic

samples

We collected nasal and pharyngeal swabs from B82 on 31 October, and nasal swabs from the other 11 bighorns on 6 November. Swabs were transported in modified Amies medium with charcoal (BBL Microbiology Systems, Becton Dickinson and Co., Cockeysville, Maryland 21030, USA) to the Colorado Veterinary Diagnostic Laboratory (CVDL) (Colorado State University, Fort Collins, Colorado 80523, USA) for bacterial isolation using standard techniques (Carter, 1984); we serotyped P. haemolytica iso!ates using the rapid plate agglutination methods of Frank and Wessman (1978). We bled all 12 bighorns on 12 November, collected serum, and submitted those samples to CVDL for serology. Titers to parainfluenza 3 (P13) were measured using hemagglutination inhibition (Rosen, 1969), and titers to bovine respiratory syncytial virus (BRSV) were measured by serum neutralization (Carbrey, 1971). One bighorn that died was necropsied, and gross and histologic lesions were described. Lung and suprapharyngeal lymph node were submitted to the Wyoming State Veterinary Laboratory (University of Wyoming, 1174 Snowy Range Road, Laramie, Wyoming 82070, USA) for bacteriology, and lung was examined by fluorescent antibody tests (Jones et al., 1978) for BRSV, P13, and Chiamydla psittaci. Data

analysis

Differences tion related

in urine and fecal cortisol excrepost hoc to clinical condition were examined by one-way analysis of variance for a completely random design with a repeated measures structure using the SAS System for General Linear Models (Freund et al., 1986). Individual animals were replicates in the analysis, and we repeated over collection periods. We assumed all effects were fixed. RESULTS Clinical course Four of 12 Q86) developed October and those animals,

bighorns (B82, pneumonia

nasal

M86, 20

7 November (Table 1). In upper respiratory signs pre-

ceded clinical pneumonia We first observed mild rous

G77, between

discharge

by 8 to 16 days. coughing and se-

in B82

on 20 October,

MILLER

1 day Within Q86) nasal ber,

before 2 days,

excreta sampling two more animals

were coughing discharge was B82 and G77

monia,

and

M86

Within

occasionally, evident. By had developed

and

and 9 days,

coughing

began. (G77,

Q86

29

showed

but no Octopneu-

pneumonia.

therapy

for

We

U

C

0

discharge. also devel-

B82

on

G77, Q86, and M86 of these four animals

began

U) I-

0 (2 OCT

ing,

developed

four

by serous no signs

31

October,

on

8 November. (B82) died

showed ble

mild

and

for

One 15 days

OCT

26-21

OCT

rhinitis

nasal discharge, of respiratory

E

20

15

10

-J

0

charac-

and disease

25

I-

four (Ta-

0

1.

FIGURE

findings

Beta-hemolytic

T was isolated swabs of all monia or mild lates included

pneumonia

P. haemolytica biotype from nasal and pharyngeal eight bighorns with pneurhinitis (Table 1); these isoboth serotypes 3 and 4. We

observed no tween serotype

apparent relationship and clinical condition

ble 1). Swabs from yielded no significant serologic

tests

the

for

P13

other bacterial and

four

BRSV

be(Ta-

bighorns growth. All were

neg-

mean

(A)

0.046)

ative. on gross

diagnosed

and

histologic

suppurative

nia accompanied by mild hepatic lipidosis, interstitial nephritis coli and a tonsillar

lesions,

we

bronchopneumo-

lymphoid depletion, and mild chronic in B82. Escherichia

Bacillus swab,

sp. were cultured from lung, and suprapharyngeal lymph node. In addition, Actinomyces pyogenes and an untyped P. haemolytica were recovered from suprapharyngeal

tibody

tests

were

negative.

lymph for P13,

node. BRSV,

Fluorescent anand C. psittaci

Mean shaded

appeared

in

Only three of four affected bighorns (G77, Q86, M86) were sampled in all three collection periods, and their data were used

showed

0.003)

=

0.046)

animals

period

(P

Mean

cortisol

affected

and

means

that

by

clinical by

bighorns

5 to 22 ng/mg mean from

affected for

and

healthy

excretion fore

clinical

for

fecal

1).

7.2 3.6

appeared

individuals. was

detected pneumonia

9.1

ratios affected

individuals; concentrations

to 20 ng/g to

mildly

Twenty-four

healthy

cortisol

0.49).

from

hour mean urine cortisol : creatinine ranged from 10 to 57 ng/mg for 24-hr

con-

collection (P

in excreta (Fig.

12-

of clinical

period

healthy

fecal the

over

or interactions

levels

el-

and

1). Differences

influenced

collection

ul-

showed

(Fig.

indistinguishable

and

of

vertical

= 0.003)

(P

grouped not

and

bighorns

grouping;

excretion

0.28)

condition

=

affected

bars)

Bighorns

period

were

mildly

pneumonia

cortisol

dition

(P

sampling

error.

urinary

sampling

fecal

represent

clinical

analyses.

mean

(B)

(open

Bars each

clinical elevated

12-day in

healthy

developed

among

the

excretion

standard

subsequent

=

and

over

and

for

+1

timately

(P

bars)

cortisol

collections are

day

developed

shaded

indistinguishable.

hr

lines

that

(P

bars)

PERIOD

bighorns

excretion

(lightly

ranged and fecal cortisol excretion

urinary

cortisol

period.

48

Three (heavily

evated

Based

NOV

OCT-I

C

COLLECTION

Diagnostic

31

5

1).

Urine

26-21

antibiotic

after antibiotic treatment began, but the other three recovered after 3 to 4 weeks of therapy. Of the eight bighorns remainterized

537

C C

21-22

oped

IN BIGHORNS

-J

frequent

serous nasal M86 and Q86

ET AL.-PASTEURELLOSIS

dry ng/g Elevated

up

matter dry

to

developed.

for

matter cortisol

16 days

be-

538

JOURNAL OF WILDLIFE

DISEASES,

DISCUSSION The

pasteurellosis

here

shares

otics

in

of

free-ranging

provide

into

bighorn pneumonia veal that elevated

complex. cortisol

pneumonia

monia

were

in

elevated

may least

disease

bighorns,

captive

when that

sampling a rise

lationship

in

warrants

Despite this not necessarily

between

Treating

than

twice

oped

pneumonia

of here)

Corticotropin-treated velop pneumonia,

(Miller,

that

unpubl.

data), responses

indices of in bighorns.

flicting

observations,

bighorns (Miller

this

in

in

ACTH

to (and

levels more

that

devel-

et al.,

1991).

nasal secrelymphocyte

in

may

represents

in be

such

an

described

factor

in

here.

However,

seems

equivocal

before

six

age. Similar patterns have in wild bighorn populations

been

pneumonia

1972; 1986).

Spraker and In addition,

months

ing pneumonia

(Demarchi,

Hibler, 1982; two P. haemolytica

could

not

of

described

rotypes (3 and 4) were recovered sal swabs of affected individuals. each strain’s relative significance

Bailey, se-

from naAlthough in caus-

be discerned

here,

presence and/or transmission of one or both may have contributed to the outbreak. Preexisting immunity to P. haemolytica may also have influenced the pattern of this epizootic. The four bighorns that developed pneumonia were among seven previously unaffected by pasteurellosis; all five sheep that had recovered from pneu-

bighad

cho,

W. vitro

inappro-

(Table 1). P. haemolytica after

1986;

pasteurellosis

(Donachie et a!.,

Confer,

immunity can de-

et 1984;

1988).

in do-

at., 1986) Cho and

Similar

and Jeri-

responses

have not been described in bighorns, but our observations suggest earlier infections may have conferred protection to some individuals that resisted pneumonia dur-

we can

only

losis probably

be elevated bein bighorns.

Protective challenge

pneumonic

sheep (Confer

ing

stress

implicate

horn lambs appear particularly vulnerable to pasteurellosis: all lambs born into our research herd between 1984 and 1986 de-

to con-

predisposing

data

predisposing

interpretation

vivo susceptibility In light of these conclude

cortisol

undeter-

when other epizootiological observations are considered. Age and/or reproductive physiology may have influenced relative susceptibility of lambs and castrated rams to pneumonia during this outbreak. Big-

mestic cattle

here

suggesting

epizootic

velop to

indistinguishable animals (M.

alone,

the

during

remains

as a dominant

outbreak against

animals

However,

stress

responses

incubation

monia in 1984 or 1985 remained healthy or were only mildly affected during this

ACTH-treated

those

cortisol excretion may pneumonia develops

Whether

and

with

excretion controls

pneumonia

responses of unaffected

priate disease that fore

elevation

1988).

developed

blastogenesis

do re-

immunosuppression but was apparently

pneumonia lymphocyte from those

findings a causal

Data collected experiments seem views of that re-

responses indicated occurred, to predispose

Miller,

our

spp. Reduced

insufficient horns

wild

sheep failed to deeven though some were

shedding Pasteurella tions (Miller, 1988). bighorns may have

or

physiological

veloped

evaluation.

bighorns

levels

blastogenesis

could prove of impend-

cortisol

elevated urine cortisol 4 to 5 times those of

some bigpneumonia

captive

association, demonstrate

be-

in cortisol

in

further

pneumonia in bighorns. during another of our to contradict traditional lationship.

recan

bighorns.

be detected 16 days before

outbreaks and

the

Our data excretion

develops. Such as association useful to managers in warning ing

of

in urine and feces that developed pneu-

demonstrating

excretion horns at

may

epizootiology

Cortisol concentrations from the four sheep gan,

epizoand

simply

subclinical mined. Examined

described

pneumonia bighorns,

insights

precede

or

outbreak

features

1991

VOL. 27, NO. 4, OCTOBER

this outbreak. Differential susceptibility

bighorn eral

exists

populations. processes

favoring

operate

pneumonia

to

among We to

and suggest create

outbreaks

pasteurelwithin two

wild gen-

conditions

in bighorn

MILLER

populations; affecting

we overall

population first process, among

to

view both susceptibility

a specific differential

bighorn

populations

explain southwest during 1984,

reyt, 1989) susceptible

how

an epizootic Canada’s bighorn 1981 to 1983 (Onderka 1988). Introduced also

been incrimoutbreaks in

are extremely of Pasteurella

spp.

strains

can

data

domestic sheep. It follows caused by novel Pasteurella initially

operate

density-independent a large proportion may be susceptible second

susceptible may increase

with and and

Onderka

by

process,

animals through

variability

within a recruitment

in social,

of

population of im(via birth individ(via stresstemporal Densitynutritional, sta(An1979).

1988; Festa-Bianchet, 1988; unpubl. data). These increases oclargely through improved lamb rethat produced young and prenaive

populations

in

a

relative

Pasteurella

pneumonia herds may

sheep episodic

responses.

in

spp.

individuals in these

periodic

epizootics reflect gradual

susceptible rather than stress

in

these populations, bouts of widespread

It seems

influence

uals

gen

the

(Anderson, discount

may

suffer

likely

that

spp.

strains Demostochastic-

periodicity

favoring densities, effects

some

individmay be epizoRelative

of

1982; May, stress completely

an outbreak: at more individ-

stressors, could

and/or

out-

1986). We in defin-

of cumulative

environmental stress responses shedding

of

some bighorn accumulation of

pathogenicity of Pasteurella may affect that proportionality. graphic and/or environmental may

inin afcases

nature

critical proportion of susceptible uals and Pasteurella spp. carriers required to propagate pneumonia otics in those bighorn herds.

breaks do not

539

in a cyclic and perfashion. We reas an outbreak of

preexisting pasteurellosis. We believe that

and quent

proportion

from

by some and that

the

Several pneumonia epizootics have followed rapid increases in bighorn numbers that could have contributed to the subsequent decline (Feuerstein et a!., 1980; Onderka and Wishart, 1984; Bailey, 1986;

sumably

arise carried herds,

ing circumstances higher ecological

reproductive, and/or immunological tus could affect overall susceptibility derson, 1979; May and Anderson

Coggins, CDOW, curred cruitment

can

pasteurellosis operates haps density-dependent gard our 1986 epizootic

ity

in a ran-

IN BIGHORNS

We believe that pneumonia occurring under these condi-

manner beof a bighorn popat any time.

munologically naive individuals or immigration) and/or through uals losing existing immunity mediated immunosuppression, waning, or some other process). dependent

spread popand strains

that bighorns to some strains

carried epizootics

Foreyt,

tions fections fected

1989). We infer (Onderka and et a!., 1988; Fo-

spp. that

In the

the

contrib-

following their association sheep (Goodson, 1982; Foreyt 1982; Coggins, 1988; Onderka

Wishart, 1988; from experimental Wishart, 1988;

dom, cause ulation

may

short time. outbreaks

Pasteurella spp. into a bighorn carrier. This may

of Pasteurella spp. have inated in some pneumonia bighorns domestic Jessup,

ultimately of a bighorn

pathogen. In susceptibility

ute to epizootics. Novel strains may be introduced herd by an immigrating partly among ulations Wishart,

as

ET AL.-PASTEURELLOSIS

social

and lead

subseto patho-

to increased

suscep-

tibility. However, we view environmental stress as one of several possible, and perhaps simultaneous, mechanisms operating on bighorn

populations

susceptibility diseases. Developing population including

to

to increase

pasteurellosis

reliable

criteria

susceptibility serologic tests

zootiological

overall and

for

other

assessing

to pasteurellosis, and refined

techniques

for

epi-

identifying

strains of Pasteurella spp., could enhance management efforts to predict and prevent pneumonia outbreaks in bighorns. Measures of stress responses could be included only

in these criteria, “stress levels” may

but fail

pneumonia epizootics in larly, management strategies “stress

reduction”

may

monitoring to predict

bighorns. targeting be

insufficient

Simionly to

540

JOURNAL

prevent

OF WILDLIFE

these

terms

of

outbreaks.

their

ceptibility, (including

on

and

carriers (Sandoval

hart, and

1970; Wishart,

Thorne 1986;

and

simulation

analyses

fox, 1976; comprehensive

Hobbs

management maintains may herd

et a!., 1979; Festa-Bianchet,

and herds

oratory

susavail(Wis-

vine

and

1990)

Stel-

suggest of habitat

effective and

epizootics

a

in minimizing preventing some in bighorns.

ACKNOWLEDGMENTS

Cortisol

bighorns.

and

creatinine

assays

were

run by the Endocrinology and Clinical Pathology Laboratories, respectively, at Colorado State University; we thank both staffs for the quality of

their

work.

We

appreciate

Dave

Bowden’s

review of our approach for analyzing cortisol data, and thank Terry Spraker and Kurt Snipes for providing archived bacterial isolates for serotyping. We also recognize the many useful suggestions jar,

provided

Warren

ymous reviews

by Dave

Snyder,

reviewers, of earlier

LITERATURE

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