BBC BLOGS - Gregory's First Law

Archives for February 2012

The science of the badger cull

David Gregory | 15:27 UK time, Monday, 13 February 2012

In a previous blogpost we looked at the statistics of bovine TB or bTB and came to the conclusion that the disease is spreading and in some counties here in the Midlands spreading very rapidly.

Which brings us to the point where the government has announced two pilot culls of badgers to control bTB, one of which will take place here in the Midlands.

Cattle and badgers all carry and transmit bTB so it sounds obvious that we need to control both to get a grip on the disease. As we saw previously we certainly slaughter enough cattle with bTB so logically the badger must be culled too. Otherwise you're just tackling half the problem.

Turns out though the wrong sort of cull makes the problem worse. We discovered that during an earlier pilot of badger culling in the region if you cull badgers when you detect bTB in a herd of cattle the infection spreads. The thinking is when you cull a family group that includes infected badgers any you miss wander off and infect other setts in areas outside the cull. Scientists call this the perturbation effect.

So the new trial culls take account of what we have learnt about the perturbation effect. They are taking place over a much bigger area and have been chosen to have features such as motorways and rivers along the edges. These measures should reduce the impact of the perturbation effect itself.

But that's not all that's changed in the cull. Other variables have been significantly altered and this leads to criticism that it's impossible to know if this new cull will work or even make things worse.

To which the government and others say in effect, "we know it works we're just trying to find a real world method we can apply" And that's true, the earlier trial did show a cull to remove 70% of badgers reduces the disease by around 16%.

As far as the government is concerned the right sort of culling works and this latest pilot cull is more concerned with whether or not those concerned can remove enough badgers in a humane and cost-effective way.

After six weeks of culling the data will be analysed and if the conditions have been met then up to ten other culls will be given the go ahead across the country. In each case the cull of badgers will be repeated every year for at least four years.

Farmers are paying the costs of this cull and must put up 125% of the estimated price. That extra 25% is to pay for cage trapping of badgers, as was used in the earlier cull, if it's found "free shooting" isn't effective.

So we come back to the motto of this blog, "science is the answer". Where does that leave us in this case?

The nightmare scenario is of course that the cull makes things worse, but that this takes some time to become apparent, a variation on what happened before. Given the differences in method between the last pilot cull and this one that is possible. It is also possible that the cull has no impact which could lead to calls for the complete eradication of badgers in hotspot areas rather than 70%.

But the government is convinced the cull will reduce bTB without spreading it further and do so in a humane and cost effective way. It can point to the results of the earlier trial and what they learnt from it and say the science has allowed them to improve the new cull and mitigate these problems. As a fallback if it's found "free shooting" is not as effective as hoped then farmers will have to go back to cage trapping. And pay for it.

And while culling any animal population is not a decision to be taken lightly badgers are not endangered and join a long list of animals we already cull for any number of reasons.

As ever with science we continue to gather the data and will have a definitive answer after a few years. Sometimes with science you have to wait.

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.

.

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.

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.

bTB graphs

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.

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