Another incidence of invasive species killing native wildlife. Sheep are allowed to graze on public lands. (what a surprise) They're also full of disease (yet another surprise). When bighorns come and graze on the same land as the sheep, the bighorns contract Pasturella a bacteria which causes the bighorns to die of pneumonia. This can cause 75% of bighorn herds to die!
Not surprisingly, Idaho denies this. In fact, Dr. Marie Bulgin a University of Idaho professor and former president of the Idaho Sheep Growers Association testified in federal court that there's no scientific evidence of domestic sheep transmitting pneumonia to wild bighorns.
An article in Science Daily talks about the research done proving pneumonia is transmitted.
The strength of this disease deters states from reintroducing bighorns. Here in Montana for example.
January 2008, a number of bighorn sheep in the Elkhorn Mountains died from pneumonia thought to have been contracted from domestic animals. Other major die-offs in Montana have been in the East Pioneers, Tendoy Mountains, Highland Mountains, Sleeping Giant Area, and Madison Range, as well as elsewhere.
So, what is being done.
In Idaho the policy is to shoot any bighorns that have come in contact with sheep and bighorns that have come into contact with that bighorn.
Here in Montana it's no different.
"Montana Department of Fish, Wildlife and Parks (MDFWP) has adopted a similar policy. For instance, prior to a reintroduction of bighorn sheep to the Gravelly Range on the Beaverhead Deerlodge National Forest near Dillon, MDFWP signed an agreement stipulating that if wild sheep had any interaction with domestic sheep, the wild sheep would be shot—and potentially even entire bighorn herds eliminated." quoted from Wild Bighorns Threatened by Domestic Sheep