Farming News - Cattle spread TB, not badgers: new research findings bode ill for government culling policy
Cattle spread TB, not badgers: new research findings bode ill for government culling policy
Groundbreaking new research suggests infected cattle missed by testing are the key element in spreading bovine TB, not badgers, though the government has dismissed these findings.
The majority of outbreaks of bovine TB within cattle herds are caused by multiple transmissions routes – including failed cattle infection tests, cattle movement and re-infection from environmental reservoirs, including infected pastures and wildlife – according to the first national model of bovine TB spread, published this week.
The model was developed by researchers at the Universities of Warwick and Cambridge, with the backing of agri-science research council BBRSC. They claim it is the first national model to track the spread of bTB, using data spanning a period between 1996 and 2011.
The researchers were investigating how bTB has become a major problem in the past 15 years. Using government data they developed a mathematical model to investigate both within- and between-farm bovine TB transmission.
In light of their findings, the researchers recommended that improved testing, vaccination of cattle and 'whole-herd culling' – where all cattle on a farm would be killed if one animal tested positive for bTB – would be the most effective strategies for controlling the disease.
In a damning indictment of the government's flagship bTB policy, badger culling, the modelling research found that whilst badgers do form part of the environmental reservoir of infection, they only play a relatively minor role in transmission, and so killing them, as experts had warned as early as 2007, can provide "no meaningful contribution" to bTB control. As well as affecting cattle and badgers, the disease can also infect deer, foxes, pigs, camelids including llamas and alpacas, domestic cats and humans.
The researchers' findings, published in the journal Nature this week, offer "A dispassionate, unbiased view of the spread of bovine TB through the cattle industry of Great Britain," according to Professor Matthew Keeling, from the University of Warwick.
Dr Ellen Brooks-Pollock from the Department of Veterinary Medicine at the University of Cambridge also commented, "By using the most recent data, our model predicts that it is most likely that both cattle movements and the local environment are driving the front of the [bTB] epidemic. Imperfect cattle skin tests contribute to the spread by delaying the time until infected herds are detected for the first time and incorrectly identifying herds as clear of infection."
One of the key results from the model is the large variation in what happens to farms once they are infected. "We found that the vast majority of infected farms don't spread the infection to any other farms before they clear infection themselves. Only a small number of farms spread the infection, and they can cause the majority of new cases", said Dr Brooks-Pollock.
Writing in The Ecologist, Professor Keeling said, "Over 90 percent of infected farms clear the infection before they cause any secondary cases, while about 2% of farms infect 10 or more other farms."
Three options to rid UK of bTB
Having explored a variety of possible options, the researchers said "There is no single panacea," but recommended that three key control options do have the power to tackle bovine TB effectively. Professor Keeling said that, though "All controls have advantages and disadvantages," a strategy to prevent bTB from spreading in the UK should revolve around, "More frequent or more accurate testing, vaccination of cattle and culling all cattle on infected farms."
Keeling added that these 'idealised' control options are only a theoretical route to stopping the spread of bTB and that researchers had not considered the practicalities or economics of implementing these measures.
The researchers estimated that whole-herd culling would drive a 20-fold increase in cattle slaughtered in its first year, which they acknowledged would have huge political, social and economic ramifications.
Even so, Farming Minister George Eustice said that, if the paper's findings were enacted, they would "Finish off the cattle and dairy industry in this country."
Defra has reportedly dismissed the research, claiming that it does not investigate the full range of ways in which bTB can spread, but the researchers maintain that, though their study combines several factors in the 'environmental reservoir of infection' – including a range of wildlife, other animal species and infected pastures – this doesn't detract from their findings.
Lord Krebs, architect of the Randomised Badger Culling Trial, whose work showed badger culling to be an ineffective means of tackling TB, told the BBC that, whilst the recommendations may be too much to implement, the study gives further support to arguments that the government's badger culling policy is misguided and that "The emphasis [of control measures] should be on stopping cattle-to-cattle transmission."
Badger Trust spokesperson Dominic Dyer, added, "The research backs up what we have been saying all along and should be the final nail in the coffin of the disastrous badger cull policy.
"The government and the farming industry have focussed far too much on badgers and nowhere near enough on the gaping holes in cattle management policy, which have been letting this disease through. We're already seeing good results in places where improved and more frequent testing, combined with movement controls and better biosecurity on farms, have been used – The road forward is clearly being signposted by these figures – so we need the government to stop reversing up the cul de sac of badger culling and actually deal with the disease in an effective manner."
Dyer added, "One fact that simply isn't being faced up to is that the skin test to identify cows infected with TB is not fit for purpose. It misses around one in five infected cows each time – which means that many TB infected cows remain in the herds, spreading the disease, or are transported to other farms or slaughterhouses without anyone knowing that they are infected."
Environment Secretary Owen Paterson took aim at vets this week, after 19 prominent vets sent an open letter to the Veterinary Record stating that the government's claims on badger culling were "seriously flawed."
The British veterinary Association, once a staunch supporter of the government's cull plans, has distanced itself from the controversial policy in recent months, stating that senior members are debating whether the Association can continue to support the badger cull, given concerns over the lack of independent oversight and use of shotguns – cull licensing body Natural England has confirmed they will be used this year, though no evidence exists to show shotguns are sufficiently 'humane'.
The policy implications of the study's recommendations have been investigated in more detail by the BBC.