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