For over 100 years, disease has significantly limited bighorn sheep (Ovis canadensis) populations in the western U.S. (Tomassini et al. 2009; Valdez and Krausman 1999). Interaction with domestic sheep (Ovis aries) has been a primary cause of fatal bighorn disease, which has severely reduced or wiped out entire populations (Tomassini et al. 2009; Toweill and Geist 1999). Preventable wild-domestic sheep interaction regularly killing large numbers of bighorns is a big problem because bighorns are vulnerable, valuable wildlife (Valdez and Krausman 1999; ODFW 2003; Wehausen, Kelley, and Ramey II 2011).

Desert bighorn ram with domestic shep in Arizona's Dome Valley

This site features a tremendous amount of information and resources covering the problem of disease transmission from domestic sheep to bighorn sheep. Here, you'll find scientific journal articles, news, policy documents, government management plans, meeting minutes, videos, maps, website links, bibliographies, case studies, die-off tables, and more. This site also features original narratives by geographer/site founder Tristan Howard. All narratives include embedded citations and reference lists.

You are now at a prime destination for reliable information on a challenging wildlife management problem. As the quotes below illustrate, wild-domestic sheep disease transmission is a grave, well-established threat to bighorns.

“Scientific research supports a finding that when bighorn sheep intermingle with domestic sheep, large numbers of bighorn sheep die. While the exact reason for this result may be in question, it is clear that the die-offs occur. An incompatibility exists between the two species and there is no way to avoid the incompatibility other than to keep the domestics and the bighorns separate.”
– United States Magistrate Judge Donald C. Ashmanskas (USFS 2008, 9)

“There is evidence that if native wild and domestic sheep are allowed to be in close contact, health problems and die-offs may occur. . . . There are native wild sheep die-offs that occur with no apparent relationship to contact with domestic sheep or goats. . . . [These] observations are both valid and not mutually exclusive.” – Bureau of Land Management (1999, 95)

“If the wildlife management objective is to keep bighorn sheep alive, absolutely no physical contact with domestic sheep should be permitted.”
– William J. Foreyt, PhD, Washington State University (USFS 2001, 4)

“Bighorn die-offs have occurred in every state in the western United States. In broad perspective, when there has been contact between apparently healthy bighorns and domestic sheep, the bighorns die within a few days to a few weeks. While many diseases or stress factors may be involved, bighorns exposed to domestic sheep almost invariably die from pneumonia.”
– Desert Bighorn Council's Technical Staff (1990, 33)

“Domestic sheep are virtually toxic to bighorn sheep. The two species have to be kept apart and cannot be permitted to share any common ground.”
– Valerius Geist, PhD, University of Alberta (USFS 2001, 4)

Bureau of Land Management (BLM). 1999. Attachment 7: 1998 Revised Guidelines for Domestic Sheep and Goat Management in Native Wild Sheep Habitats. In Challis Resource Management Area: Record of Decision and Resource Management Plan. Salmon, ID. http://www.blm.gov/pgdata/etc/medialib/blm/id/plans/challis_rmp.Par.8185.File.dat/ entiredoc_508.pdf (accessed May 12, 2012). [govt. doc.]

Desert Bighorn Council Technical Staff. 1990. Guidelines for the management of domestic sheep in the vicinity of desert bighorn habitat. In transactions of DBC’s 34th Annual Meeting, Hermosillo, Sonora, Mexico. April 4-6.

Tomassini, Letizia, Ben Gonzales, Glen C. Weiser, and William Sischo. 2009. An ecologic study comparing distribution of Pasteurella trehalosi and Mannheimia haemolytica between Sierra Nevada bighorn sheep, White Mountain bighorn sheep, and domestic sheep. Journal of Wildlife Diseases 45, no. 4 (October): 930-940.

Toweill, Dale E., and Valerius Geist. 1999. Return of royalty: Wild sheep of North America. Missoula, MT: Boone and Crockett Club and Foundation for North American Wild Sheep.

U.S. Forest Service (USFS). 2001. A Process for Finding Management Solutions to the Incompatibility Between Domestic and Bighorn Sheep, by Tim Schommer and Melanie Woolever. N.p. http://www.fs.fed.us/biology/resources/pubs/wildlife/bighorn_domestic_ sheep_final_0806 01.pdf (accessed January 5, 2012). [govt. doc.]

U.S. Forest Service (USFS). 2008. A Review of Disease Related Conflicts Between Domestic Sheep and Goats and Bighorn Sheep, by Timothy J. Schommer and Melanie M. Woolever. Fort Collins, CO. http://www.fs.fed.us/qoi/documents/2009/CWGA-zpfile000.pdf (accessed October 15, 2011). [govt. doc.]

Valdez, Raul, and Paul R. Krausman, eds. 1999. Mountain sheep of North America. Tucson: The University of Arizona Press.

Wehausen, John D., Scott T. Kelley, and Rob R. Ramey II. 2011. Domestic sheep, bighorn sheep, and respiratory disease: A review of the experimental evidence. California Fish and Game 97, no. 1 (Winter): 7-24. http://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=4651 1(accessed May 23, 2012).