Disease has infiltrated Hunt District 622 in Montana. Last week, Montana Fish, Wildlife and Parks (FWP) reported that two rams – one harvested by a hunter last fall and another found dead during FWP’s spring survey – tested positive for Mycoplasma ovipneumonia, the bacteria that causes pneumonia in bighorn sheep and typically results in massive die-offs.

“This is disappointing news for this herd, which has been one of our strongest in recent years,” said FWP Region 6 supervisor Drew Henry.

While other respiratory tract bacteria have been found in bighorn sheep in that hunting district, this is the first time M. ovi was detected. 

“Pneumonia can cause all-age die-offs and chronic infections in adult and lamb bighorn sheep. This can persist for many years within a herd,” said Dr. Jennifer Ramsey, FWP wildlife veterinarian. “This situation is very complicated and not completely understood because we also have robust herds infected with M. ovi and other pneumonia-causing bacteria, and we do not see population impacts.”

FWP closed HD 622 earlier this month because of a “dramatic loss of population,” according to the agency. HD 622 is located on the north side of the Missouri River Breaks in northeast Montana. For the past two years, biologists have noticed a decline during aerial counts and hunters reported seeing sick sheep in 2024. 

FWP will continue to monitor the remaining bighorn sheep in this district.