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Brucellosis: What are Economists doing?|College of Agriculture and Natural Resources

 

Brucellosis: What are Economists doing?

By: Carolyn Hageman and Dannele Peck

Dannele Peck, an associate professor in the Department of Agricultural and Applied Economics in the College of Agriculture and Natural Resources, has committed roughly eight years to studying the economics of brucellosis in Wyoming.

Peck was hired to start a new research program on this important topic. She began by focusing on the costs of a cattle herd contracting the disease. Former graduate student Bryan Wilson worked on estimating those costs for his thesis. He focused on the costs of brucellosis if: a) an infected herd was de-populated, b) an infected herd was quarantined for 12 months, and c) a herd was quarantined for one or six months because of potential exposure to a neighboring infected herd. Peck will publish results in extension bulletins.

 “If a cow in your herd is detected as being seropositive, that is they have antibodies to brucellosis, your herd will be quarantined immediately,” Peck said. “If a cow is proven to be infected, that is the bacteria can be cultured from its tissues, the herd will be quarantined until the entire herd passes three consecutive tests for brucellosis, typically over a 12 month period. In the past, an infected herd would instead be depopulated, culling both infected and uninfected animals. However, depopulation is a very expensive approach to preventing the spread of brucellosis, so USDA-APHIS has moved away from it, favoring quarantines now. ”

Quarantined herds are not allowed to graze any pasture that borders another herd. “For some ranchers, this would mean keeping their herd on a small part of the ranch, that might have insufficient grazing resources, for 12 months or longer,” said Peck. “You can imagine the amount of feed you might have to buy in such a situation and how expensive that would be.”

“Imperfections in the existing tests for brucellosis are why we have to do these expensive 12-month-long quarantined processes, or de-populate the whole herd. If we could figure out a perfect test that worked immediately, most of the cost of brucellosis would go away,” said Peck. After a positive blood test, a seropositive animal has to be slaughtered and their tissue samples cultured. If Brucella abortus bacteria grow from the tissue samples, the animal is “culture positive” and definitely had the disease. If no bacteria grow, the samples are “culture negative,” which means either the animal did not have brucellosis, or the tissue samples were simply inadequate. The Brucella bacterium is notorious for being difficult to culture in a lab setting.

After an infected cow or elk aborts their fetus, the bacteria can persist in the environment for up to eight weeks under sufficiently cool and dark conditions. A curious cow, investigating the site of a brucellosis-related abortion, may accidentally ingest or inhale the bacteria. If the dose is high enough and their immune response is inadequate, the animal can become infected. So another question economists are working on involves the costs of prevention activities, such as fencing stackyards (to discourage elk-cattle commingling), adult-booster vaccination of cattle with RB51, delayed grazing in higher risk areas, and other measures.

While Wilson’s thesis work has provided a better understanding of the financial consequences a rancher could face if their herd contracted or was potentially exposed to the disease, they also need to know the cost of various brucellosis-prevention practices.

Brucellosis: What are economists at UW doing?“My second graduate student, Trent Roberts, was tasked with figuring out how much it costs to implement various prevention activities,” said Peck. “Imagine there was something you could do to prevent your herd from getting brucellosis. How much should you be willing to pay for that management practice?” said Peck. If a rancher’s herd of 400 breeding cows (plus additional calves, yearlings, and replacement heifers) contracts brucellosis, and they are quarantined for a year, Peck and Wilson estimate it would cost about $140,000, largely because of hay costs (assuming the historical average hay price of $89/ton). 

“But keep in mind a cattle herd is not guaranteed to catch the disease, even if they are within Wyoming’s brucellosis Designated Surveillance Area,” says Peck.  “So, to make a good investment decision about brucellosis-prevention activities, a rancher also needs some sense of the chances of their herd catching the disease.” 

“Suppose you think your herd faces a risk of contracting brucellosis once during the next 100 years. This implies a 1 percent chance or 1/100 chance of catching the disease in any particular year,” says Peck. “Assuming a quarantine cost of $140,000, your expected cost per year of getting brucellosis would be $1,400 (or $140,000/100). That is, to be financially prepared for one 12-month quarantine sometime during the next 100 years, you should save $1,400 annually.”

After calculating the costs of different management practices, Peck and Roberts discovered some prevention activities are just too expensive, relative to the expected cost of contracting brucellosis, to justify investing in them. That is, for some activities, the cost of the cure is worse than getting the disease. Delayed grazing and hiring someone to keep elk away from spring and early summer grazing areas do not make financial sense for most ranchers. However, management practices such as fencing stackyards, adult booster vaccination, spaying heifers, and calling the Wyoming Game and Fish Department to haze elk off of private property in the winter are inexpensive enough that their benefit (a reduction in the risk of contracting brucellosis) might possibly outweigh their costs. This depends, though, on how much brucellosis risk a herd initially faces.

Economists in the College of Agriculture and Natural Resources are still in the process of determining the cost-effectiveness of various brucellosis prevention and management activities. Graduate student Shane Ruff recently finished his thesis on the potential benefits and costs of switching from a cow-calf-yearling operation to a stocker steer operation (because steers and spayed heifers are exempt from brucellosis testing). His results are summarized in UW Extension bulletins MP-126.1 through MP-126.3. Graduate student Kari Boroff recently finished her thesis on the cost-effectiveness of various elk management strategies for reducing seroprevalence in elk. Her work is being drafted into future UW Extension bulletins. Peck’s overall goal is to give ranchers and wildlife managers practical information they can use to determine which brucellosis prevention or management activities might be worth considering and which are most likely to give them the biggest bang for their buck. 

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Brucellosis: What is UW doing?

College of Agriculture and Natural Resources researchers at the University of Wyoming continue to study brucellosis.

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