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Thursday, April 12, 2018

Study looks at why Montana's bighorn sheep are still plagued by die-offs

Montana study examines bighorn sheep die-offs and challenges some long-held theories about bighorn sheep management and exposure to pathogens.


 "Garrott — along with several MSU colleagues and Montana Fish, Wildlife and Parks research biologist Kelly Proffitt — has been attempting to answer that question, along with others including nutrition and habitat, with a 10-year study of bighorn sheep in the Greater Yellowstone Ecosystem as well as a six-year study of eight herds spread across Montana. The scientists’ theories are challenging what have been some long-held beliefs about bighorn sheep management.
Chief among them is that bighorn sheep are carriers of pathogens that, when conditions are right, can lead to significant herd die-offs from respiratory disease. The pathogens are believed to have been originally transmitted to bighorns by interactions between domestic sheep and goats. Bighorns had no immune defense against the pathogens, resulting in sharp population declines.
If the wild sheep have been exposed to the pathogens since the late 1800s, though, why have they still not developed a stronger immune response? Garrott said he thinks it’s similar to the flu bug that humans fight on an annual basis. The flu bacteria is constantly changing, frustrating health officials as they try and develop vaccines to annually protect humans.
According to their sampling efforts, Garrott said about 80 percent of bighorn sheep are carriers of the pathogens, but unless the animals are stressed or suffer from poor nutrition, it’s not a problem.
“The protocol right now is we can eliminate die-offs if we keep them separate from domestic sheep,” Garrott said. “That’s created a lot of political pressure to get domestic sheep off of public lands.”
But he said the bighorns have the ability to die all on their own, without commingling.
“Perhaps we shouldn’t be pointing an ugly finger at domestic producers,” he said."