In 1994, an environmental impact statement collaborated by the US Fish and Wildlife Service, National Park Service and the US Forest Service, was signed to reintroduce gray wolves to central Idaho and Yellowstone National Park.
Since then, the wolf population has boomed across the western region and proved to be problematic for livestock producers.
According to the Montana Fish, Wildlife and Parks, there were 51 confirmed cattle kills, 15 probable cattle kills, 24 confirmed sheep kills and 7 probable sheep kills in the state in 2013.
On top of hitting ranchers" finances with livestock death rates, a recent study conducted by Oregon State University (OSU) has found cows exposed to wolves are less likely to become pregnant.
""When wolves kill or injure livestock, ranchers can document the financial loss," said Reinaldo Cooke, an animal scientist in OSU's College of Agricultural Sciences, in an Extension article. "But wolf attacks also create bad memories in the herd and cause a stress response known to result in decreased pregnancy rates, lighter calves and a greater likelihood of getting sick. It's much like post-traumatic stress disorder – PTSD – for cows."
The study involved 100 cows – 50 came from the Council, Idaho area from a herd that has confirmed wolf experiences and 50 came from Eastern Oregon Agricultural Research Center which has no reported wolf experiences – both groups came from herds where trained working dogs were utilized.
In a 20 minute simulated wolf encounter, the separate groups of cows were held in a pen exposed to wolf urine while a stereo played recorded wolf howls. During this time, three leashed dogs resembling wolves were kept 25-5 m from the fence – dogs did not vocalize or act aggressive during the encounter.
Afterwards, cows were individually held in a squeeze chute that had been exposed to wolf urine, while the howling was again played, and were exposed to the leashed dogs.
In a series of measurements, researchers found cortisol levels, a stress induced hormone, elevated by 30 percent in the Idaho cows that had previous wolf experiences. The study noted these cows were also more excitable during the simulation, compared to the previous non-exposed cow herd which maintained normal cortisol and activity levels.
Typically, livestock producers practice low stress handling for not only animal welfare purposes, but profitability. Studies have shown cattle under low stress conditions are more efficient, healthier and more likely to become and remain pregnant.
In 2010 OSU published an analysis of estimated economic losses to ranchers due to wolves in five counties of northeast Oregon.
Along with noting, "Confirmed losses generally are reported to be 1 confirmed carcass for every 8 actual losses," it also found the ranchers had the potential to lose $261 per head of cattle. This included $55 for shrink associated with wolf exposure and $67 for decreased pregnancy rates.
"In a herd, if you are not raising calves, your cows are not making you money," said David Bohnert, an expert in ruminant nutrition at OSU's Eastern Oregon Agriculture Research Center in Burns, in the Extension article. "With stress likely decreasing the proportion of those getting pregnant and causing lighter calves from those that do, a wolf attack can have negative financial ripple effects for some time."