Epidemiologic Findings and Management Response During a Bighorn Sheep Die-Off in the Elkhorn Mountains of West-Central Montana

Scientific Disciplines
Biological Sciences - Terrestrial
Montana Department of Fish, Wildlife and Parks
nature & environment
bighorn sheep
domestic sheep
mule deer
gastrointestinal parasites
elkhorn mountains
elkhorn mountains westcentral
mountains westcentral montana
elkhorn mountains westcentral montana
bighorn sheep dieoff
Volume 16, No. 4

Epidemiologic findings and management response during a 
bighorn sheep die-off in the elkhorn mountains of west-
central montana

Neil Anderson,* Deborah L. McCauley, and Jennifer Ramsey, Montana Department of Fish, 
Wildlife and Parks  1400 South 19th Ave., Bozeman, Montana 59718  
Tom Carlsen and Fred Jakubowski, Montana Fish, Wildlife and Parks, 56 Manor Drive, Townsend, 
Montana 59644
Jenny L. Sika, Montana Fish, Wildlife and Parks, 930 Custer Avenue West, Helena, Montana 59620
Bighorn sheep (Ovis canadensis) were introduced into the Elkhorn Mountains of west-
central Montana in the mid 1990s.  The population increased in number to approximately 
250 animals until the winter of 2007-2008 when about 84 percent of the population died 
from a pneumonia related epizootic. Management actions during the die-off were geared 
toward removing as many sick animals as possible in efforts to reduce overall mortality. 
Due to the stage of the epizootic removal of sick sheep was not effective in interrupting the 
die-off. Samples were collected from bighorn sheep, domestic sheep, mule deer (Odocoileus 
hemionus), elk (Cervus elaphus) and domestic goats utilizing the same winter range.  
Pasteurella  spp, Moraxella ovis and Mycoplasma ovipneumonia were isolated from lung 
tissue of dead bighorns and pharyngeal swabs collected from domestic sheep occupying 
similar range during the epizootic.  Both the bighorn sheep and domestic sheep also shared 
similar gastro-intestinal parasites including Nematodirus spp and Eimeria spp. Testing tissues 
and fecal samples from sympatric mule deer suggested no shared bacterial pathogens and 
limited shared gastrointestinal parasites. Evaluation of fecal samples from domestic goats 
and elk also occupying bighorn sheep range identified few shared parasites that may have 
contributed to the epizootic.