Researchers simulated a wolf encounter that included dogs.
Researchers simulated a wolf encounter that included dogs.

Cows that have witnessed wolf attacks display physical signs associated with post-traumatic stress disorder, according to a new study by Oregon State University.

PTSD is a psychological disorder that develops in some people who have experienced a shocking, frightening or dangerous event. This is the first study of its kind to reveal PTSD biomarkers in cattle.

The findings are published in the Journal of Animal Science.

“Wolf attacks 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,” said Reinaldo Cooke, an animal scientist in OSU’s College of Agricultural Sciences who led the study.

After they were reintroduced to Yellowstone National Park in the last two decades, gray wolves have dispersed through the West and have hunted in livestock grazing areas. Oregon’s wolf population has grown steadily since wolves migrated to northeast Oregon. The state visually documented 112 wolves at the end of 2016. Wolves west of U.S. 395, U.S. 95 and Oregon Route 78 are protected by the U.S. Endangered Species Act.

OSU researchers have heard anecdotes from ranchers that cows that have come in contact with wolves eat less and are more aggressive and sickly. In this study, cows at the Eastern Oregon Agricultural Research Center (EOARC) in Burns were exposed to a simulated wolf encounter and their brain and blood were analyzed for biomarkers, in this case, expression of genes, associated with stress-related psychological disorders, including PTSD.

The research builds on a 2014 study led by Cooke, showing that cows that had been exposed to wolves showed more fearful behavior even when they had not been attacked. The latest findings confirmed the researchers’ hypothesis: the cows’ stress response was expressed in certain biomarkers in their blood and brain cells linked to PTSD in humans and other mammals. Similar research has been conducted with rodents exposed to potential predators.

In their latest 2016 study, researchers simulated a wolf encounter with 20 Angus crossbred cows to appraise the stress of a wolf attack. Half of them were raised at the EOARC and had never seen a wolf, and the other half had been part of a commercial herd in Idaho that was previously attacked on the range. None of the Idaho cows had been directly attacked or injured by wolves.

Both sets of cows were gathered separately for 20 minutes in a pen scented with wolf urine while pre-recorded wolf howls played over a stereo. Three trained dogs – two German shepherds and one adult border collie-Alaskan malamute mix – walked outside the pen.

“The cows previously unfamiliar with wolves showed no signs of agitation and actually approached the dogs,” Cooke said. “They also didn’t have biological signs of PTSD, according to PTSD-related biomarkers evaluated in their blood or brain tissue.”

Multiple studies from Cooke and other researchers have established a link between cow stress and poor performance traits that can cost ranchers. The researchers call for further research into ways of successfully managing both wolves and livestock so they can co-exist.

The Oregon Beef Council funded the study.