One of the most contentious wildlife management debates in the United Kingdom is whether badgers must be killed in order the slow the spread of tuberculosis (TB) in cattle, a disease that costs farmers and taxpayers about £120 million a year. Farmers insist the culling is necessary, because badgers can spread the disease to cattle. Wildlife advocates counter that the practice is inhumane and can make the problem worse.
A new review of the issue, released today, reaffirms that badgers are partly responsible, but urges farmers to do more to protect their herds and prevent inadvertent spread of the disease. “It is wrong to put all the blame on wildlife,” said population biologist Charles Godfray of the University of Oxford in the United Kingdom, an author of the review. “This is a disease that needs action on all fronts.”
Bovine TB is the “most pressing animal health problem in the U.K.,” according to the review. The strain that infects cattle is killed by pasteurizing milk, but sick animals produce less milk and lower quality meat. Infected animals are typically killed. The disease been particularly difficult to control in the United Kingdom and is getting worse, in part because badgers are also susceptible. The bacteria can spread between cattle and badgers that live near farms. In 2014, the U.K. government launched a 25-year strategy to eradicate the disease with a combination of testing, controls on cattle movements, and a controversial plan to kill badgers. The justification for the culling comes from a large randomized trial that took place between 1998 and 2005. It found that culling can reduce the number of TB cases in cattle, but only if at least 70% of the badgers around a farm are killed. Killing fewer can disrupt the social structure of badger communities, causing some to travel farther away and potentially spread the disease.
The Department for Environment, Food, & Rural Affairs (DEFRA), which oversees the control program, believes the results of two pilot culls are promising and has expanded the effort. Skeptics aren’t convinced that the 70% target has actually been reached in all places. In 2017, workers caught and killed some 20,000 badgers in 20 parts of England. (Wales and the other devolved nations each have their own strategies.) The government this year increased the number of licenses and now allows badgers to be controlled, either by killing or by vaccinating the animals against TB, in 32 areas. Meanwhile, some 30,000 infected cattle were killed last year.
In February, DEFRA commissioned an external review of its strategy to evaluate progress and additional actions that could be taken. Although the agency didn’t ask reviewers to analyze the ongoing badger culls, the report briefly addresses the controversial issue. The authors reiterated that the best evidence comes from the Randomized Badger Culling Trial, showing a “modest but real effect” in reducing the number of new outbreaks by about 15%. “If a decision is made to cull,” the review finds, “then carrying it out over sufficiently large geographic areas to reduce the relative effects of perturbation and utilizing natural barriers to badger movement, as is done at the moment, is in our view correct.” Less is known about how well vaccination works, the panel said, and the government could consider running a large trial. “We desperately need more evidence about the efficacy of vaccination,” Godfray said.
The review notes that far more cases of TB result from transmission between cattle than from badgers, so it urges DEFRA and farmers to do more to control bovine TB on farms. Cattle can be protected by keeping badgers from contaminating their feed, for example, and by using better fences around their pastures. And farmers can prevent introducing TB into the countryside by better management of manure. But so far, the implementation of these relatively cheap measures has been “disappointingly low,” the review finds, perhaps because of a fatalistic view about living with the disease and a sense that it is a government problem. This lack of farmer involvement is “severely hampering” efforts to control the disease.
Another key strategy is not inadvertently transporting infected cattle to other areas. DEFRA already requires testing for TB before cattle are moved from high-risk to low-risk areas, but the review suggests expanding the testing zone and switching to a more sensitive kind of test, which would reduce the number of false negatives. “Evidence is accumulating that there is more infection circulating in the national herd than we previously realized,” Godfray said. (Better tests for TB in cattle should be a high priority for research, the report noted.) In addition, farmers who buy cattle should be informed if they are coming from a high-risk area. A new national tracking system for cattle should make this feasible, in addition to revealing insights into how the disease spreads. The government should also consider reducing compensation for the slaughter of infected animals, as this might provide a disincentive to trading of cattle from high-risk areas.
The report makes “many strong and bold proposals to improve cattle TB control,” says Rosie Woodroffe, an ecologist at the Zoological Society of London. But she is skeptical that a robust trial of vaccination can be done in places that have already experienced culling, because it would increase the prevalence of TB among badgers and therefore could make vaccination less effective. Matt Keeling, an epidemiologist at The University of Warwick in Coventry, U.K., predicts the recommendations in the report will have “huge policy implications.” DEFRA expects it will need a few months to evaluate the review and respond.