Goldilocks - When to kill a Cull.

Not the fairy tale girlie, with three bears, Goldilocks is also the description of the principle of getting the outcome of a scientific process  'just right'. Described in Science Daily, -[link] the Goldilocks principle is one of balance to achieve the desired outcome.

So how does this relate to badgers, cattle and zoonotic Tuberculosis?

Published on March 6th, The Royal Society - [link] described a paper entitled 'When to kill a Cull'. Apart from a title which gave us pause for thought, that does relate to badgers, cattle and the control or eradication of zoonotic tuberculosis. The paper explains:

Culling wildlife to control disease can lead to both decreases and increases in disease levels, with apparently conflicting responses observed, even for the same wildlife–disease system.     There is therefore a pressing need to understand how culling design and implementation influence culling's potential to achieve disease control.

We address this gap in understanding using a spatial metapopulation model representing wildlife living in distinct groups with density-dependent dispersal and framed on the badger–bovine tuberculosis (bTB) system.

We show that if population reduction is too low, or too few groups are targeted, a ‘perturbation effect’ is observed, whereby culling leads to increased movement and disease spread. We also demonstrate the importance of culling across appropriate time scales, with otherwise successful control strategies leading to increased disease if they are not implemented for long enough.

The paper is modelled - and some of the hieroglyphics, although pretty, are beyond our editors, but in a nutshell we glean that if you do a rubbish cull on a grossly infected population, you spread disease through perturbation, whereas if you cull all infected individuals - wipe out, then zoonotic tuberculosis disappears. But so do badgers.

The Goldilocks banding in bright yellow is the modelled ideal.


Below some of the modellers calculation  tools, and their Goldilocks charts.

Now going back to 1997, when the notorious RBCT Badger Dispersal Trial began, launching into an infected population for 8 nights only, annually if you were lucky, all this was known.

Especially to the chief bear, who led the group, the diminutive Professor John Bourne, who delighted in informing politicians - [link] on the EFRA committee that the outcome of his trial was known before it started, and that it was designed in such a way to protect badgers.




'When to kill a Cull' indeed. That charade was Goldilocks in action.

And we also know from the answers to Parliamentary Questions that the Thornbury trial which culled for 8 months, and removed most of the badgers in that area using underground group euthansia, kept cattle clear of zTB for at least ten years. And that the reason it was so successful was:

" The fundamental difference between the Thornbury area and other areas [] where bovine tuberculosis was a problem, was the systematic removal of badgers from the Thornbury area. No other species was similarly removed. No other contemporaneous change was identified that could have accounted for the reduction in TB incidence within the area" [157949]

So back to Goldilocks, and one could say, another wodge of money spent stating the obvious.

This is a chart of various badger culling exercises, and their effect on cattle TB over the last four decades.

So basically, if you are going to cull an infected group of animals, do it thoroughly, for long enough and over an appropriate area .. or you end up making things worse. Simples isn't it?