Cows seeing wolf attacks suffer stress symptoms

Cows seeing wolf attacks suffer stress symptoms

UNLIKE cows that have never had a run-in with wolves, cows that have can experience stress-related illnesses and have a harder time getting pregnant, meaning decreased profits for ranchers, according to a new study by Oregon State University.

"When wolves kill or injure livestock, ranchers can document the financial loss," said Reinaldo Cooke, an animal scientist in Oregon State's College of Agricultural Sciences. However, "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 for cows."

After a reintroduction to Yellowstone National Park in the last two decades, grey wolves have dispersed throughout the West and have hunted in livestock grazing areas. Since then, Oregon State researchers have heard anecdotes from ranchers that cows that have come into contact with wolves are more aggressive, sickly and eat less.

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

Cows were gathered in a pen scented with wolf urine while prerecorded wolf howls played over a stereo and three trained dogs — German shepherds closely resembling wolves — walked outside the pen.

Researchers found that levels of cortisol, a stress hormone, increased 30% in cows that had previously been exposed to wolves. They bunched up in a corner, formed a protective circle and acted agitated. Their body temperatures also increased rapidly, another indicator of stress.

On the other hand, the cows previously unfamiliar with wolves were curious about the dogs and did not show signs of stress.

Multiple studies from Cooke and other researchers — including recent research from the University of Montana (Feedstuffs, Feb. 17) — have established a link between cow stress and poor performance traits that can cost ranchers.

A 2010 Oregon State 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 extension agent in Wallowa County who conducted that study. It can be read online at

"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 Oregon State's Eastern Oregon Agriculture Research Center in Burns, Ore. "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 are calling for further research into ways of successfully managing both wolves and livestock so they can coexist.

Results of the wolf/cow simulated encounter study, which was funded by the Oregon Beef Council, was published in the Journal of Animal Science and was co-authored by Cooke and Bohnert.


Salmonella in feedlots

Salmonella is a recognized pathogen that can cause substantial morbidity and mortality in cattle feedlots. Salmonella is also associated with foodborne illness in people.

In U.S. beef production, post-harvest intervention strategies are aimed at lowering the occurrence of salmonella and all foodborne pathogens in meat and meat products.

Recently, however, interest has increased in examining pre-harvest strategies that could augment the effectiveness of post-harvest strategies. A better understanding of salmonella's ecology in the feedlot production environment could help identify effective pre-harvest control strategies.

The U.S. Department of Agriculture's National Animal Health Monitoring System (NAHMS) conducted the "NAHMS Feedlot 2011" study, and one of its objectives was to describe the prevalence and antibiotic resistance of salmonella found on U.S. cattle feedlots.

The NAHMS feedlot study provided an in-depth look at large feedlots (1,000-head capacity or more) in 12 states and small feedlots (less than 1,000-head capacity) in 13 states. Large feedlots accounted for 82.1% of the Jan. 1, 2011, inventory of cattle in all U.S. feedlots but only 2.8% of all feedlots. The 12 participating states accounted for more than 95% of the 2011 cattle inventory in large feedlots.

During the study, a subset of 68 large feedlots consented to salmonella testing. On each of the 68 feedlots, three pens of cattle were identified for sampling: the pen that had been in the feedlot the shortest amount of time, the pen closest to harvest and one pen selected at random. Up to 25 individual fecal samples were collected from each pen floor. The samples were cultured for salmonella, and any salmonella isolates were characterized by serogroup, serotype and antimicrobial resistance profile, NAHMS said.

The salmonella results were recently released.

Salmonella prevalence. In total, 5,050 individual samples were collected from 202 pens in the 68 feedlots. Overall, one or more samples tested positive for salmonella on 60.3% of the 68 feedlots, and 35.6% of sampled pens were positive for salmonella, NAHMS reported.

There was no substantial difference in pen-level salmonella prevalence based on the length of time cattle were in the feedlot, NAHMS explained. For pens of cattle that had been in the feedlot the shortest amount of time, salmonella prevalence was 39.7%, compared with 33.3% of randomly selected pens and 33.8% of pens closest to harvest.

At the sample level, the overall prevalence was 9.1%. There was no substantial difference in sample-level prevalence based on pen type (time in the feedlot). For pens in the early part of the feeding period, the sample-level prevalence was 8.5%, compared with 9.0% for randomly selected pens and 9.8% for pens closest to harvest, NAHMS said.

A total of 571 salmonella isolates from 460 positive samples were further characterized.

The three most common salmonella serotypes isolated from the individual fecal samples — Anatum, Montevideo and Kentucky — accounted for 50.4% of the total isolates (Table 1). Each of the other serotypes identified represented less than 10% of isolates.

Antimicrobial resistance of isolates. Most salmonella isolates (74.6%) were susceptible to all antimicrobial agents tested (Table 2), NAHMS said, adding that when resistance was present, it was usually to a single antibiotic (15.9% of isolates). Overall, less than 10% of isolates were resistant to each of the antimicrobial agents tested, with the exception of tetracycline (21.4% of isolates were resistant) and sulfisoxazole (13.1%).

Summary. Based on the results of the "NAHMS Feedlot 2011" study, the overall prevalence of salmonella cultured from fecal samples was 9.1%, with no differences based on the duration of an animal's stay in the feedlot, NAHMS said. However, salmonella was widely distributed, with 35.6% of pens and 60.3% of feedlots having at least one positive sample.

Most of the salmonella isolates (50.4%) were attributable to three serotypes. Overall, most salmonella isolates were susceptible to all antimicrobial agents tested. When resistance was present, though, it was most commonly to tetracycline or sulfisoxazole.

NAHMS concluded that the overall prevalence of salmonella reported in the latest feedlot study was similar to the prevalence found during its 1999 feedlot study in which 6.3% of samples tested positive for salmonella.


1. Number and percentage of isolates, by serotype



% isolates

















2. Number and percentage of isolates (571 samples) resistant to the following antimicrobial agents







Amoxicillin clavulanic acid



























Nalidixic acid












Trimethoprim sulphamethoxazole



*Resistance was determined using breakpoints reported in the 2011 National Antimicrobial Resistance Monitoring System report.


Volume:86 Issue:11

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