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Why are bighorn and domestic sheep hanging out? Here's why we should care.

A respiratory illness common in domestic sheep can devastate wild bighorn sheep herds. Now a pair of MSU researchers is studying how wild and domestic sheep interact.

Researchers at Montana State University have been studying the domestic and bighorn sheep interactions, but recently received $4 million in university funding to initiate the latest research. Photos by Diane Renkin and Martin Schmidli. Illustration by Julia Barton
Researchers at Montana State University have been studying the domestic and bighorn sheep interactions, but recently received $4 million in university funding to initiate the latest research. Photos by Diane Renkin and Martin Schmidli. Illustration by Julia Barton
EDITOR'S NOTE: This article has been updated to include statements and context from FWP disease ecologist Emily Almberg.

by Julia Barton

The bighorn sheep is a muscular and athletic denizen of mountainous and arid terrain across the western U.S. This hardy ungulate is also remarkably susceptible to diseases spread by their wooly, domestic counterparts. In an effort to mitigate the spread of disease, a new research project in Montana aims to better understand where and how often wild and domestic sheep interact.

Montana State University has been studying bighorn and domestic sheep in Greater Yellowstone for years, according to MSU Extension wildlife specialist Jared Beaver, who explained that research involves a variety of stakeholders including conservationists, state agencies, hunters and livestock owners. The university awarded $4 million to kickstart the latest round of research, led by Beaver and MSU Extension sheep specialist Brent Roeder in collaboration with Montana Fish, Wildlife and Parks.

“Oftentimes with very complex and nuanced wildlife issues, it's easy to see if it's an ecological or biological question,” Beaver told Mountain Journal. “But when you have a lot of stakeholders invested, there's a lot of social and cultural components to it as well, and it makes these studies very dynamic.”
Symptoms related to the bacteria M. ovi are typically mild among domestic flocks of sheep, but can be devastating to wild bighorn herds.
The disease prompting this research, and other similar studies, is a respiratory illness caused by Mycoplasma ovipneumoniae bacteria, or M. ovi for short, that can cause pneumonia in sheep and goats, and predispose animals to other respiratory complications. Symptoms are typically mild among domestic flocks, though they’ve caused substantial economic losses for livestock producers. Impacts on wild herds can vary drastically, ranging from mild to “devastating,” according to Beaver.

Respiratory diseases have likely been present among bighorn sheep since domestic sheep were first brought to the U.S. in the 15th century, said FWP disease ecologist Emily Almberg. The pneumonia found in sheep is polymicrobial, meaning various bacteria are present in sick animals, and it was unclear what the causative agent was until M. Ovi was linked to the disease in the early 2000s.

“Not all disease introduction events result in massive die-offs,” Almberg said. “We have documented M. Ovi introductions that cause no detectable disease. The majority of them, as far as we know, seem to cause some disease … you can have very catastrophic impacts to some herds where they lose 50 to 70 percent of the herd.”

At least 22 epizootics, or outbreaks, among 43 herds were documented in Montana between 1979 and 2013, according to a 2015 paper.
"[M. ovi introductions can] have very catastrophic impacts to some herds where they lose 50 to 70 percent of the herd.”  – Emily Almberg, Disease Ecologist, FWP
There are two approaches for disease transmission research, according to Beaver. The first explores ways to improve the health of chronically infected herds. A successful example of this work has been removing members of a herd that continually test positive for M. Ovi baceteria, Almberg explained. The second focuses on minimizing contact in the first place.

“Our work falls in the latter category because that has the potential to yield wins for both bighorn and domestic sheep,” Beaver said. “It's a first step of what we hope will start to involve other researchers that are looking at improving performance of chronically infected herds.”

Once the details of how interactions between wild bighorns and their privately-owned kin are better understood, land managers with Montana Fish, Wildlife and Parks can tailor management protocol to minimize interactions and subsequent disease transmission, according to Beaver. The current recommendation is to keep roughly nine miles between domestic and wild herds.

“As the landscape becomes increasingly more populated and fragmented, allowing for that much space really isn't always feasible,” Beaver said. “It's certainly not feasible if we want to continue to try and restore bighorn sheep numbers across the West, so our first step is simply getting a better understanding of how contact is occurring.”

The MSU endowment will fund researchers and GPS collars to track movement of bighorn sheep, domestic sheep and livestock guardian dogs. Beaver emphasized the collaborative backbone of the project, which will take account of anecdotal evidence from long-time livestock producers in the state and involve other stakeholders as needed. And it’s starting here in the Treasure State.

“Montana is leading the charge,” Beaver said. “The ultimate hope for everyone involved is that we can find adaptive management strategies that benefit wildlife managers, producers and the wild and domestic sheep themselves.”

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Mountain Journal is the only nonprofit, public-interest journalism organization of its kind dedicated to covering the wildlife and wild lands of Greater Yellowstone. We take pride in our work, yet to keep bold, independent journalism free, we need your support. Please donate here. Thank you.

Julia Barton
About Julia Barton

Julia Barton is a freelance journalist and communications specialist based out of Bozeman. A Montana native, she earned a journalism degree from the University of Southern California and reports on the environment, outdoor recreation and the arts.
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