Wildlife managers are racing to assess the scope of a potentially devastating disease outbreak after a deadly respiratory bacterium was detected for the first time in the John Day River bighorn sheep herd — Oregon's largest, with an estimated 1,000 animals — raising urgent concerns among hunters, ranchers, and tribal wildlife managers across Central Oregon.
The Oregon Department of Fish and Wildlife confirmed last week that several bighorn sheep from the herd recently tested positive for Mycoplasma ovipneumoniae, commonly known as M. ovi — a respiratory pathogen capable of causing fatal pneumonia-like illness in sheep. In some populations, an M. ovi outbreak can kill a significant portion of a herd within a single season, with lambs particularly vulnerable.
First Known Detection in This Herd
The John Day River herd has long been considered one of Oregon's healthiest bighorn populations, making the detection all the more alarming. ODFW confirmed these are the first known cases of M. ovi in the herd's recorded history.
Wildlife biologists are conducting necropsies on animals that have died, sending tissue samples to the Washington Animal Disease Diagnostic Laboratory for strain identification — a critical step, because some M. ovi strains are far more lethal than others. Field teams are also surveying the John Day River canyon for additional sick or dead animals.
In related cases in Baker County, ODFW officials are working to identify "chronic shedders" — sheep that carry and transmit the bacteria without showing outward signs of illness themselves.
Warm Springs Tribes Join Management Response
The Confederated Tribes of Warm Springs, alongside the Confederated Tribes of the Umatilla Indian Reservation, are partnering with ODFW to evaluate the findings and develop a containment and management plan.
Bighorn sheep hold deep cultural significance for the Warm Springs Tribes, and the herd's range in the John Day River canyon lies in proximity to the reservation and tribal hunting grounds. Tribal wildlife managers will play an active role in determining how to protect remaining animals and prevent spread to adjacent herds.
What Hunters and Residents Can Do
ODFW is asking anyone who spots sick or dead bighorn sheep in the John Day River canyon or surrounding areas to report the sighting as soon as possible.
- ODFW Prineville office: (541) 447-5111
- Report location, time, number of animals, and any visible symptoms
- Do not approach or handle sick or dead animals
The situation remains under active monitoring. ODFW says it will provide updates as lab results and field surveys return more complete data on the outbreak's extent.