Montana Fish, Wildlife and Parks (FWP) is seeking answers behind the near die-off of the Middle Missouri Breaks bighorn sheep herd in HD 622, as previously reported. Emily Almberg, a FWP disease ecologist, called the incident “a perfect storm from an epidemiological perspective,” adding that “the rapid die-off of a herd that was once free of the bacteria…is consistent with a group of animals that hadn’t previously been exposed.”

Tests run on both a hunter-killed ram and another captured this spring tested positive for Mycoplasma ovipneumonia, or M. ovi, is the bacteria behind bighorn sheep die-offs across the West. Wild sheep become infected after mingling with domestic sheep and goats, which are carriers of the bacteria.

“It’s hard to say what proportion of the decline we can ascribe to M. ovi,” said Almberg. “We have herds with M. ovi that are doing okay for a long time and we don’t know why.”

One important aspect of this particular die-off is the detection of a new strain of M. ovi in the hunter-killed ram by researchers at the Washington Animal Disease Diagnostic Laboratory (WADDL) where samples were sent for testing, according to the Moscow-Pullman Daily News.

“It’s not a perfect match with anything WADDL has sequenced before,” said Almberg, noting that the new strain likely still came from domesticated sheep or goats as variations of M. ovi are often found in these animals even though they aren’t usually found in wild sheep.

“Potentially, the strain could point to where it came from,” said Almberg. “But strain diversity even in a flock can be high.”

Fortunately, for the survival of the once healthy herd, there are still a few bighorn sheep remaining. FWP reported four rams during the spring survey and asks anyone who spots a bighorn sheep in the area to call 406-228-3700 to report it.