Yakima Bighorn Sheep are Experiencing an All Age Die-off

Source of disease is unclear.

Bighorn Sheep © Ken Cole
Bighorn Sheep © Ken Cole

The bighorn sheep in Central Washington’s Yakima River Canyon are dying of pneumonia. It appears likely that ODFW officials will try to stop the epidemic by killing the infected animals so that they won’t infect healthy bighorns.

Two Stories
Big decision on bighorns
Scientists may have to thin the herd in order to save it from disease

What’s the source of pneumonia in bighorns?



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  1. jdubya Avatar

    ok, so where are they getting the mycoplasma from? i thought reporters were supposed to ask questions instead of just writing verbatem what some academic says.

    Questions for Mr. Sandsberry to ask next time:

    1. What is the source of the pasteurella that can infect bighorns?
    2. What is the source of the mycoplasma ovipneumoniae?
    3. Can domestic sheep carry both without signs of disease?
    4. Can bighorns carry both without signs of disease?

  2. Ralph Maughan Avatar


    I’ll bet that just like the East Fork of the Bitterroot, domestic sheep are going to raise their ugly “infectious” head here too.

    Mycoplasma are a type of bacteria that have no cell wall. Mycoplasma ovipneumoniae is a widespread disease of domestic sheep and all their wild ancestors. Domestic sheep are very likely to carry the disease without being sick. Bighorn usually get sick especially when it is combined with pasteurella, which is mostly a disease of rabbits, and which bighorn can carry without illness.

  3. Petticoat Rebellion Avatar
    Petticoat Rebellion

    Logic tells us that the disease has to be introduced from another host species that is less susceptible because this disease exhibits extreme virulence in the bighorns. Therefore, it could not be possibly be sustained in populations of wild bighorns.

  4. Wilderness Muse Avatar
    Wilderness Muse

    The Yakima River herd is in two groups one down near the Roza Diversion, on the west side close to the town of Yakima. The other is on the opposite side of the River closer to Ellensburg, maybe 15-20 miles of separation. Hopefully, the herd on the east side is healthy, and the disease won’t jump the river.

    I saw the third, the Clemens herd, on Christmas Day. They are behind an elk fence and their habitat is straight up hill from there, on some pretty steep and inhospitable rock and scree, until you hit the top of Clemens where there is sparse timber. It is just about four miles east of the junction of hiways 410 and 12 near the junction of the Naches and Tieton Rivers. This is about thirty miles away from the Roza herd. These animals are at the lower elevations on Mt. Clemens, close together now, as the Department of Wildlife feeds them when the snow gets deep – no snow yet. Hopefully they can avoid the fate of the Yakima Roza herd.

    To my knowledge none of these three herds are exposed to domestic sheep.

  5. Wilderness Muse Avatar
    Wilderness Muse

    On re-reading my post, the Clemens herd is “…about 1 mile east of the junction of hiways 410 and 12…” Not 4 miles.

    Concentrating the animals for winter feeding cannot be good for this situation.


Ken Cole is a 5th generation Idahoan, an avid fly fisherman, wildlife enthusiast, and photographer. He is the interim Idaho Director for Western Watersheds Project.

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Ken Cole