Five western states have faced outbreaks of pneumonia in 11 separate bighorn sheep herds since late 2009,? with nearly 1,000 having been killed or died due to the disease, reports the Wildlife Management Institute. The die-offs come at the same time that researchers at Washington State University in Pullman were able to document direct transmission of one strain of pneumonia-causing bacteria, Mannheimia haemolytica, between domestic sheep and bighorn sheep in a controlled environment. These situations are causing state fish and wildlife agencies and federal land management agencies to evaluate and adapt management practices continually in order to reduce the risk of further bighorn die-offs.

In June 2010, the Western Association of Fish and Wildlife Agencies' (WAFWA) Wild Sheep Working Group reported on the nine specific outbreaks in bighorn sheep herds in Montana, Nevada, Utah, Washington and Wyoming. Their summary documents each outbreak from the 2009-10 winter, with details on number of sheep killed. At the time, an estimated 888 had been culled, found dead or assumed dead (based on herd counts before and after the outbreak) from an estimated 1,600 to 1,700 animals in the herds before the die-offs. In late August, two additional herds in Montana were identified with potential pneumonia outbreaks. One proved to be a non-event, with three culled and no additional sick animals observed. The other, near Anaconda, has had approximately 20 bighorns? culled or found dead as of late September, and the herd remains actively monitored.

The connection between bighorn die-offs and proximity to domestic sheep or goats continues to raise concerns and challenges for wildlife managers. "While direct evidence of co-mingling may not be available in every circumstance, at least three of the nine bighorn die-offs were preceded by known or likely association between bighorn sheep and domestic sheep or goats," the WAFWA Working Group reported. ?"In many instances, domestic sheep and/or goat hobby herds or farm flocks occur on the periphery of occupied bighorn range, while in others, grazing allotments or use of domestic sheep/goats for fuels management and/or noxious weed control may have placed wild and domestic sheep in close proximity, on or adjacent to public lands where bighorns reside."

Significant research has been underway to isolate the pathogens most responsible for the pneumonia outbreaks and to identify how those pathogens enter the wild sheep herds. While past research has shown that bighorns died from pneumonia when commingled with domestic sheep, there has not been a specific study that conclusively documents that the killing pathogens came from the domestic animals. ?This summer, scientists at the? Washington State University in Pullman published a study in the Journal of Wildlife Diseases that used a fluorescent tag on the bacteria M. haemolytica in domestic sheep. When domestic sheep with the tagged bacteria commingled with bighorn sheep, all bighorn sheep died within two to nine days from contact date and the tagged bacteria was found in each. "These results unequivocally demonstrate transmission of M. haemolytica from domestic to bighorn sheep, resulting in pneumonia and death of bighorn sheep," the study's authors concluded.

Yet, keeping the sheep separate can be a challenge for state and federal agencies. "Efforts are underway in most western states and provinces to achieve or maintain effective separation between wild and domestic sheep," said Kevin Hurley, WAFWA Wild Sheep Working Group Chair from Wyoming.

The Montana Fish Wildlife and Parks Department completed its bighorn conservation strategy in April 2010, which calls for lethal removal of bighorns that have associated with domestic sheep or goats. However, the strategy mainly focuses on maintaining herd health through separation of domestic and wild sheep. Their plan closely mirrors the recommendations of WAFWA's Wild Sheep Working Group, which, in late July of this year,? released its revised "Recommendations for Domestic Sheep and Goat Management In Wild Sheep Habitat." The recommendations are intended to assist the Bureau of Land Management, U.S. Forest Service and other land managers with development of a more-unified policy on grazing domestic sheep or goats in wild sheep habitat.

"We acknowledge that not all disease outbreaks in wild sheep are the result of contact with domestic sheep or goats," the report states. "Nevertheless, there is sufficient evidence of disease transmission from domestic sheep or goats, followed by substantial mortality, that range overlap and potential association should be prevented."

On July 28, shortly after the WAFWA Working Group recommendations were released, and based on years of data collection, analysis, and modeling,? the Payette National Forest in Idaho released a Final Supplemental Environmental Impact Statement (SEIS) that will eliminate domestic sheep grazing on 68,718 acres of the forest by 2013. The SEIS will expand the buffer to protect the bighorn sheep population within the forest to 346,000 acres. In making its decision, the Forest Service cited the growing body of evidence that? demonstrates bighorns in close proximity to domestic sheep are at extreme risk for disease transmission.

"Many federal land management agencies and state wildlife managers recommend the elimination of shared use of ranges by bighorn and domestic sheep," said Suzanne Rainville, Payette National Forest Supervisor in a written release. ?"By separating the species, and reducing the risk of contact, it will be possible to have both livestock grazing and a healthy population of bighorn sheep." ?(jas)