Witnessing wolf attacks gives cows PTSD like symptoms

Stress hormones released can have lasting effects

Cows that have had a encounters with wolves can experience stress-related illnesses and have a harder time getting pregnant, according to a new study by Oregon State University. This has the potential to decrease profits for ranchers.

“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. “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 past two decades have seen a reintroduction of grey wolves into Yellowstone National Park. Since then, they have dispersed through the West and have hunted in livestock grazing areas. OSU researchers anecdotal evidence from ranchers that cows that have come in contact with wolves are more aggressive, sickly and eat less.

To measure the stress of a wolf attack, and estimate any lingering effects on cows, researchers simulated a wolf encounter with 100 cows. Half which had never seen a wolf, and half which had been part of a herd that was previously attacked.

Cows were gathered in a pen scented with wolf urine while pre-recorded wolf howls played over a stereo. Three trained dogs – German Shepherds closely resembling wolves – walked outside the pen.

Researchers found that cortisol, a stress hormone, increased by 30 per cent in cows that had previously been exposed to wolves. The cows bunched up in a corner, formed a protective circle and acted agitated. Another indicator of stress was that their body temperatures rapidly increased. In comparison, the cows previously unfamiliar with wolves were curious about the dogs and did not show signs of stress.

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Multiple studies from Cooke and other researchers have established a link between cow stress and poor performance traits that can hurt ranchers’ pocketbooks.

A 2010 OSU economic analysis estimated that wolves in northeastern Oregon could cost ranchers up to $261 per head of cattle, including $55 for weight loss and $67 for lower pregnancy rates, according to John Williams, an OSU extension agent in Wallowa County who conducted that study. The full study can be found online here.

“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. “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.”

Both researchers call for further studies into ways of successfully managing both wolves and livestock so they can co-exist.

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