RENO, Nev. (AP) — Nevada state wildlife veterinarian Peregrine Wolff worked at zoos in the Midwest, with farm animals in Florida and exotic species on movie sets in Hollywood. She never dreamed she'd have to help pull the trigger on a contentious strategy to slaughter a diseased herd of bighorn sheep.
Ed Partee, a state game biologist who's spent much of his 24-year career rebuilding bighorn populations, drew the grim task of tracking and gathering the carcasses of the 27 sheep. The animals were gunned down from a helicopter in February in an emergency attempt to save a neighboring herd.
"Having to kill an animal like that is probably one of the worst feelings I've ever had in this job," said Partee, a native Nevadan who grew up fishing and hunting and knew by the time he was in junior high that he wanted to be a wildlife scientist.
Now, they wait to see if their gamble paid off in a race against the spread of pneumonia that's also hit bighorns in Washington, Wyoming, Utah, Idaho, Montana and Utah, and threatens efforts to rebuild native populations that were on the brink of extinction a half century ago.
About 2 million bighorn sheep roamed North America before numbers started declining in the late 1800s to about one-tenth of that today due primarily to overhunting, habitat loss and disease — often transmitted by domestic animals.
"It's been a concern since the Old World European settlers started bringing their domestic sheep with them across the West," said Wolff, president of the American Association of Wildlife Veterinarians.
She suspects Desert bighorns in northwest Nevada contracted the biological agents that spread the pneumonia from domestic sheep or goats, as has been the case elsewhere. That's been a point of contention in Montana and Idaho, where ranchers and conservationists have been fighting for decades over management of domestic sheep that biologists blame for transmitting the disease.
Livestock producers suffered a setback in March when the 9th U.S. Circuit Court of Appeals upheld a 2010 U.S. Forest Service decision to protect bighorns in Idaho's Payette National Forest by closing 70 percent of the domestic grazing allotments.
The Idaho Wool Growers Association had argued that the service failed to consult the Department of Agriculture's research service before it pushed 10,000 sheep out of the area, running many ranchers out of business.
It's a "heated topic that has vast socio-economic and ecological impacts in the western United States," said Maggie Highland, a USDA animal disease researcher at Washington State University.
She's among those who question the science and wonder whether Nevada acted prematurely, "without really understanding all of the factors that caused the first outbreak."
"I'd also question how we know for certain that none of the members of the affected herd hadn't already intermingled with the herd that they were reportedly trying to protect," Highland wrote in an email to AP.
Skeptics include Mark Thurmond, professor emeritus of veterinary epidemiology at the University of California-Davis.
"What they are doing is illogical — to say we found these agents therefore we've got to eradicate this entire herd," Thurmond said. He says disease transmittal involves a complex combination of multiple agents and outside impacts, ranging from drought and wildfires, to extreme cold and snow.
"If the herd is doing well otherwise, why destroy the gene pool that has been able to handle these agents?" he told AP.
But by all accounts, the Nevada herd was not doing well.
State officials knew if they didn't act fast, the sheep would disperse as the snowpack melted. Partee said they were lucky to get an early warning of trouble in December because they'd just fitted several sheep with radio-signal collars in a partnership with Oregon to monitor movement across state lines.
"You could tell right away there was something not right because of the fact they weren't moving," Partee said. "Within weeks we started realizing we were at the start of a devastating disease event."
Necropsies confirmed the dead animals had pneumonia. Others were in such bad shape that Wolff was "surprised they were still alive."
"In January, we started talking about the fact that if we lost this herd, it would be tragic, but if it spread to the neighboring herd to the south, we'd lose both of those," Wolff said.
By the time the decision was made to kill the herd, fewer than a third of the 100 animals remained and those were so weak that they barely attempted to flee when the helicopter approached.
The move wasn't without precedence. British Columbia killed a herd in hope of saving others in 2000. Utah officials killed 25 in 2010, and Washington 63 in 2013.
Wolff consulted experts, including those in British Columbia, before conceding that killing the herd was the only hope to keep the disease from spreading in the state with the most bighorns in the Lower 48. Nevada is the only state with all three North American species — Desert, California and Rocky Mountain.
Early indications are the kill may have kept the disease from reaching the neighboring herd.
Wolff stands by the decision.
"I take exception to anyone in the domestic sheep industry looking over my shoulder and telling the Nevada Department of Wildlife how to manage," she said. "I totally understand the politics. But to deny the science because of the politics is sort of short-sighted to me."