It is a bacteria called mycoplasma ovipneumoniae. It is apparently common in domestic sheep and goats, but easily causes fatal pneumonia in bighorn sheep. Story Organism ID’d That May Be Killing Bighorn Sheep. By Keith Ridgler. AP. (as printed in the Seattle Post Intelligencer).
“All indications are that the domestics are passing diseases and killing off the bighorns,” said [Greg] Dyson [Hells Canyon Preservation Council]. “And the bighorns just can’t get a foothold to become re-established. There have been entire herds that have died off.”
In May a lawsuit by the Western Watersheds Project, and two other groups, forced the Forest Service to stop their planned turnout of domestic sheep into the range of the struggling bighorn in Hells Canyon on the Idaho/Oregon border.
If people want to see a more general restoration of bighorn sheep on their public lands, the bands of domestic sheep in these territories simply have to go.
See earlier stories.