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Bovine TB. Crunching the numbers.

David Gregory | 16:06 UK time, Thursday, 9 February 2012

Bovine TB or bTB is a very nasty disease. For people and for animals both domestic and wild. For that reason it's a notifiable disease, which means if you have a case on your farm you have to tell the government. Combined with a stringent and regular testing programme for cattle we have a remarkable amount of data on the disease.

Well usually. But thanks to a computer glitch at the Animal Health and Veterinary Laboratories Agency in Worcester we haven't had any new data since September 2011. It seems odd that the government has announced a cull of badgers to tackle bTB and we don't actually have an up to date picture of what is going on.

But if we take the assurances of Defra and Animal Health and Veterinary Laboratories Agency at face value then this lack of data isn't a problem for the cull and they have promised it will soon be resolved.

Which brings us to the badger cull and the science behind it. The headline facts show that bTB is a huge problem for Britain's cattle farmers. This is from Defra's own website.

"Nearly 25,000 cattle were slaughtered in England last year alone because of bovine TB, with the cost to the taxpayer set to top £1 billion over the next ten years. The problem is particularly bad in west and south-west England, where nearly a quarter of all cattle farms were affected by the disease during 2010."

With a cull happening here in the Midlands what is the disease doing here? Well we can break things down county by county thanks to all that data collected by Defra which you can find here


Two graphs showing number of cattle culled and herds under movement restrictions to control bTB in the Midlands.

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These two graphs show the number of cattle slaughtered to control the disease in the Midlands and the number of herds affected by movement restrictions put in place because the disease has been detected. I've selected the data from 2002 onwards since the foot-and-mouth crisis in 2001 caused all sorts of problems with bTB testing. Even without the latest data we can still observe much from the trends over eight years.

In the Midlands overall, however you measure it, bTB is a growing problem with a clear upward trend in the worst affected counties. Indeed Staffordshire and Shropshire show particularly alarming rises over the past eight years.

Is there perhaps some good news in that the last few years show a dip in terms of cattle numbers slaughtered for some counties? It will be very useful when the data for 2011 is finally released to be able to say more about this. But at the moment it's hard to be hopeful, indeed this drop might just be down to the fact there are fewer cattle around to slaughter. Cow numbers are declining as farmers in the dairy sector continue to struggle, not least because of bTB.

So the data (well what we have!) shows there is clearly a problem. In the next post I look at whether a cull is the right solution.

Comments

  • Comment number 1.

    Whether the updated figures show a rise or a fall in bTB figures the Government won't change tack. In what is essentially a politically motivated decision they are intent on fulfilling an election manifesto promise. Their justification for the pilot culls is littered with assumptions and half truths. They promised a science-led cull. They are delivering the opposite: the figures on which they base their assumptions (a 12-16 per cent fall in bTB over NINE years) were based on cage trapping and shooting. The proposed culling method is "free shooting" an untried method for which, obviously, they have no figures on which to base a calculation. Their prediction is simply guesswork. Only politicians could claim it is science-based. They promised a "balanced" package of measures. What have they delivered? A six-week badger slaughter to find out if "free shooting" (that's another name for using badgers as target practice) works and virtually nothing else, nothing that will make any inroads into the huge untouched reservoir of disease which even they admit is not the result of disease transmission from badgers. Almost every media and newspaper report starts with the phrase "badgers are blamed for spreading" TB. Rarely do any commentators tell the public that, at worst, badgers are only a fringe issue. The real cause of bTB spread is cattle-to-cattle transmission and for that there are all sorts of reasons: the "skin" test is only 80 per cent effective--so inevitably it misses disease in a herd, that disease eventually is picked up by a later test...and of course the farmer concludes it must be badgers to blame. Defra urges biosecurity measures and Fera research has shown conclusively it works. Are farmers (who expect us to compensate them) putting those measures in place? No--or at least, too few of them. Told to keep badgers out of their feed storage barns and to double- fence their boundaries, they claim it's too expensive. So we, the taxpayers, pick up the bill for compensating them.Independent scientists (ISG) urged gamma interferon testing alongside the skin test and were adamant that farmers with clean herds should buy only cattle from herds of equal status. In other words their message was if the farmer with cattle to sell has a poor history of bTB DON'T buy from him--chances are you'll be importing disease. Wait until he has gone two or three years without a TB breakdown. Countryfile, through its presenter and NFU award winner Adam Henson, has continually emphasised or impied the alleged role of badgers and has refused to give equal prominence to cattle-to-cattle transmission and all the problems inherent in the current cattle management system. No wonder Henson had a special mention from Caroline Spelman when she announced the cull. Just one more aside, David: you repeatedly say the culls will go ahead in later summer. Well, they may do, but do remind your followers that the Badger Trust has announced it will take legal action (it will seek a judicial review) unless the Government changes its approach. The badger is an easy target in media terms; but bTB is much more complicated than that and the public should be told, by among others, the BBC. And scientists like yourself might choose to examine Jim Paice's claim that no country in the world had eradicated bTB without tackling it in wildlife. Well, no country has yet eradicated bTB; the examples he quotes of possum in New Zealand and water buffalo in Australia are to, mix metaphors, red herrings. New Zealand has literally tens of millions of possum which quickly keel over when ineffected, shedding bacteria as they die. Badgers have a high degree of resistance. MOST badgers are TB free and only a very small percentage of those infected go on to be potentially or actually infectious. bTB is rarely fatal in badgers (the claim that hundreds are dying a slow painful death is another myth the Government likes to spread). Perturbation is probably a unique characteristic of badgers and absolutely key to solving bTB and deciding whether culling them works. Science says very clearly it doesn't and what's more, that the disease can be beaten by cattle-based measures alone. So, come on, give the badger a better media deal--and that includes the BBC (Countryfile and the Archers among them).

 

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