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Disease & Separation


Testing wild sheep for disease near Troy, Oregon
There are many threats to our wild sheep populations, including habitat loss, lack of reliable water in arid zones, predation (e.g., mountain lions, coyotes, golden eagles), and human disturbances on winter range (e.g., unregulated off-road/ATV use, back-country or heli-skiing). By far, the biggest threat is the disease transmitted from domestic sheep to wild sheep, oftentimes resulting in respiratory pneumonia and all-age die-offs.

Mycoplasma Ovipneumoniae (Movi) is a pathogen that can be carried by domestic sheep and transferred by animal-to-animal contact with wild sheep. Movi weakens a wild sheep's immune system, making them susceptible to death by pneumonia. Young lambs are most vulnerable once Movi is introduced to a herd, but all-age die-offs often occur within a population.
There is no cure or vaccination for Movi. At present, the best preventive measure is keeping the ranges of wild and domestic sheep from overlapping to reduce the risk of contact. Improved lamb survival has been demonstrated by removing Movi-infected bighorn sheep from a population to stop the pathogen from being continuously transferred to non-infected sheep. Areas with little to no lamb survival each spring are now seeing lambs making it past 6 months, but more data over longer timeframes is essential.
Doctors, farmers, biologists, and volunteers come together to fight a deadly disease threatening both wild and domestic sheep in this feature documentary presented by the Wild Sheep Society of BC. Learn more at


Dr. Tom Besser was appointed January 1, 2016, to a 3-year term as the WSF Rocky Crate Chair for Wild Sheep Disease Research at Washington State University. Dr. Besser's focus is on Movi. In Year 1 of Dr. Besser's appointment as Rocky Crate Chair, WSF provided $50,000 to support Tom's programs and research associates. Dr. Besser's research will generate additional information and data to aid wild sheep managers in their efforts to improve chronically-poor lamb survival and recruitment, and to work toward effective spatial and temporal separation between domestic sheep and goats and wild sheep.


For decades, WSF and our network of Chapters and Affiliates have advocated for effective temporal and spatial separation between wild sheep and domestic sheep and/or goats.
WSF has: 
  • Advocated for and partnered on dozens of voluntary domestic sheep grazing allotment waivers in multiple states. WSF has engaged the domestic sheep industry and individual permittees, seeking collaboration and trying to improve relationship-building and common understanding. 
  • Worked hard with federal and Crown land management agencies, state, provincial, and federal wild sheep managers and respective legislatures, our strong network of Chapter and Affiliate leaders, and others to craft long-term solutions designed to achieve and maintain effective separation in time and space.
  • Provided funding through its Grant-in-aid Program for continued disease research and surveillance and Test & Remove projects.


WSF World Headquarters | 412 Pronghorn Trail | Bozeman, MT 59718 USA | Phone: 406.404.8750 (800-OK-FNAWS) | Email:

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