andygates: (badger)
[personal profile] andygates
I've been trying to get my head around the numbers involved in the bovine TB drama.  The take-home number from the Government's Randomised Badger Cull Trial (the Krebs trial) is a reduction of up to 16% in bovine TB after nine years of culling.

Let's say you've got a medium-large dairy herd, 200 cattle.  Let's say you have really bad TB, and 10% a year are culled as TB "reactors" (cattle that react to the test).  20 cattle per year.  At the end of a decade of culling badgers across your land by the Krebs method, you have 17 reactors: 16% is really lost in the rounding on such small numbers.  So you spend nine years culling on your land, hiring people to do it, faffing with paperwork, dealing with saboteurs, and after all that you've saved three cows a year? 

That can't be worth the effort. 

It gets worse.  The cull method that DEFRA propose isn't the Krebs method: it's widely agreed to be less effective.  It's not been tested, but instead of trapping it goes for wild shooting with ample chance of perturbing the local badger population.  Perturbing the population - stirring 'em up - spreads disease and makes things worse for cattle and badgers both.

The rational response is to abandon the cull and pour effort into the ongoing badger TB vaccines being trialled at, for example, Killerton in Devon.  That's what the Welsh farming office are doing.  That's what the English should be doing too.

Date: 2012-07-20 12:29 am (UTC)
From: [identity profile]
The problem of course is getting this through to people who have their heads so firmly up their arses they can check the backs of their own front teeth for cavities.

Date: 2012-07-20 05:15 pm (UTC)
From: [identity profile]
Aye. It's a hot-button topic round here for sure. Could be an entertaining couple of years.

Date: 2012-08-08 12:14 am (UTC)
From: (Anonymous)
If you have 200 cattle...and you get really bad TB... eg 10 positive infected. They quarantine the whole herd, execute the lot (all 200), and start testing all your neighbours and everyone in something like 20 mile radius. And that's for patient-Zero. Then depending on your local system, the entire zone goes on lockdown and movement control. No animals are allowed to leave the zone without individual tests, and certainly not to saleyards or stockshows. This state stays until several years pass and the tests are clear. And for the duration all the beef importers in other countries devalue your entire countries product. It might be somewhat more lenient in your area, and they might only cull "suspect" rather than wholesale herds.

The philosophy behind the carrier culls, is that TB between human control animals can be isolated into these zones and progressively reduced. But there still exists random vectors which spring up and create new infections in zones that have been clear for years. By reducing the vector population they hope that it will result in "herd protection" - ie infected animals will have less contacts within their own population. And any carriers will be limited in how many infections, and feedback infections (butterfly wings), they can cause. TB is a good example as it likes dense populations. Confine the spread to a few patients ( 0 & 1) in the wild population, then unlikely to have the pathogen numbers to successfully wipe out expensive chunks of your cattle industry, and also reduce the small likelihood of bTB transferred to humans. And if you don't care about human infection, or the expensive chunks of the local cattle industry then I'm pretty sure they would feel the same to anything you regard as important.

It is overkill, but it's a hard pathogen to stop.

Date: 2012-08-08 08:27 pm (UTC)
From: [identity profile]
That lockdown doesn't describe what we see here.

Date: 2012-08-16 02:16 am (UTC)
From: [identity profile]
Ok. Sounds like they're trying to copy our methods though (re wild life). We don't have badgers, but we do have possums which can transfer bTB. Having a positive test is about the biggest way to piss off the neighbours as even a "Suspected" will downgrade everyone in your local zone, with mandatory vet testing and paper trail for everyone in the neighbourhood. Once one gets a "suspected" result, then they have to test to "Clear"status, then that's retested every 1-3 years and recorded as C1 - C10. Importing an animal from a lower C zone can cause your own rating to be dropped to the lowest (despite all animals being Clear). I'm currently C3, as someone stuffed up the paperwork when the larger farm was split in two (the other half got the C10 paperwork, and no-one re-registered this half so we had to apply afresh, and prove on paper we're Clear.) It's a bit inconvenient because people see the C3 and get worried that there was detected case in the herd/area.
Also the vaccines can stuff up the detection tests, which would hide outbreaks. Sadly the real problem is too many bureaucrats getting paid to police these systems and come up with symptom control (like murder badgers) than efforts to develop new ways to fix the problem.


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