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Bighorn sheep were widespread in regional canyons prior to their extirpation, now have been reintroduced to rebuild populations.

E.g. Hells Canyon pioneers found bighorn more common than deer. Numbers were estimated at up to 28,000, but now roughly only 1,100.

Population crash caused by:

  • Diseases (especially pneumonia, most important factor preventing recovery today)

  • Competition with livestock

  • Market hunting

  • Habitat Degradation

Mycoplasma ovipneumoniae (Movi) is now recognized as the bacterium that triggers fatal bighorn sheep pneumonia outbreaks, although many other bacteria contribute to disease and death. Movi infection is the necessary first step of an outbreak.

Domestic sheep and goats are the most important sources of Movi for infection of bighorn sheep, based on the high rates of infection, the diversity of strain types that they carry, and the observation of pneumonia following contact with bighorn sheep. Recently, Movi has been reported at low frequency in some other wild and domestic hoofstock, but these other sources have not yet been shown to play an important role in the bighorn sheep disease.

Movi usually causes no obvious disease in domestic sheep/goats and is not harmful to people. Recent studies have shown, though, that Movi infection is associated with decreased productivity and increased disease losses in domestic sheep.   

Isolated healthy bighorn sheep populations are free of Movi, but highly susceptible to disease following exposure

 If susceptible bighorn sheep become infected with Movi:

  • 20 – 80% of bighorn sheep of all ages die with pneumonia within a few months. After a big die-off, recovery may take years or decades to occur.

  • After the die-off, some surviving adults continue to carry Movi, which can infect and cause pneumonia in lambs, resulting in up to 100% lamb mortality for years afterwards. (E.g., Black Butte in Hells Canyon for 18 years).

 Currently and the foreseeable future: no effective vaccine for either bighorn sheep or domestic sheep/goats.

 Sheep and goats can contact bighorn sheep when:

  • Estrus: domestic ewes can attract young rams during rut

  • Dispersal: young rams leave to seek new herd and bighorn habitat is contiguous with people

  • Social: domestic sheep may escape, join wild sheep

  • Feed/water/salt

  • Domestic flock within normal home range of a bighorn herd

To prevent disease, keep bighorn sheep SEPARATED from sheep and goats or get sheep/goats from a known M.ovi free herd such as those from WA State Penitentiary herd study

 Even one interaction risks Movi transmission. E.g. wandering Asotin bighorn ram, lost/escaped domestic sheep and goats.

If bighorn sheep are observed contracting domestic sheep/goats, they should be removed to prevent transmission to the rest of the herd. If you observe bighorn sheep near your animal, please contact WDFW/ ODFW/ IDFG as soon as possible.

WDFW/ ODFW/ IDFG cannot and will not take livestock but seeks to work with small flock owners to minimize risk of disease transmission to bighorn sheep.