Badgers and bovine TB: the science

Defra officials continue to claim that 'the science' supports a badger cull - but what exactly is 'the science' they refer to? 

On this page you will find a summary of some of the key scientific evidence - which does not support badger culling as a viable strategy for controlling TB in cattle.  All of the papers mentioned here are available to download in full at the bottom of this page.

1. General overview

A restatement of the natural science evidence base relevant to the control of bTB in Great Britain, Godfray et al. 2013

This review paper summarises the existing natural science evidence base relevant to the control of bTB and presents it in terms that are as policy-neutral as possible.  Written by a team of leading scientists, this is a thorough and very readable overview of the science base (and gaps in it) and is an excellent place to start.
 

2. Culling badgers

The Randomised Badger Culling (Krebs) Trial, 1998 - 2005 

On the basis of our careful review of all currently available evidence, we conclude that badger culling is unlikely to contribute positively, or cost effectively, to the control of cattle TB in Britain

The most important scientific evidence comes from the Randomised Badger Culling Trial (RBCT), also known as the Krebs trial, which ran from 1998 to 2005.  It was funded by the Government and compared the effects of proactive, reactive and no culling across ten sets of sites in England. 

Lord Krebs, who designed the RBCT, concluded that that “culling is not a viable policy option”.

The RBCT reached two main conclusions:

"First, while badgers are clearly a source of cattle TB, careful evaluation of our own and others’ data indicates that badger culling can make no meaningful contribution to cattle TB control in Britain.  Indeed, some policies under consideration are likely to make matters worse rather than better.

"Second, weaknesses in cattle testing regimes mean that cattle themselves contribute significantly to the persistence and spread of disease in all areas where TB occurs, and in some parts of Britain are likely to be the main source of infection.  Scientific findings indicate that the rising incidence of disease can be reversed, and geographical spread contained, by the rigid application of cattle-based control measures alone."

The conclusions of the RBCT are available to download below, contained within the Final Report of the Independent Scientific Group on Cattle TB - 'Bovine TB: The scientific evidence.'
 

The duration of the effects of repeated widespread badger culling on cattle tuberculosis following the cessation of culling, Jenkins et al. 2010

This study examined the level of bTB incidence in and around RBCT areas after culling ended. It states:

"Beneficial effects inside culled areas were greatest shortly after culling ended, but then declined over time and were no longer detectable four years after the last annual cull (ie three years into the post-trial period).  On adjoining lands, the effects of culling were estimated to be beneficial only for the first 18 months of the post-trial period but never significantly so."

3. The perturbation effect

Culling disrupts the organisation of these social groups, increasing the risks of disease transmission

Badgers typically live in social groups of four to seven animals with defined territorial boundaries.  Culling disrupts the organisation of these social groups, increasing the risks of disease transmission as shown below.

This is known as the 'perturbation effect'.  The Independent Scientific Group on Cattle TB concluded in its final report (2007) that it was "unable to conceive of a system of culling, other than the systematic elimination, or virtual elimination, of badgers over very extensive areas, that would avoid the serious adverse consequences of perturbation".

Download our leaflet on the perturbation effect below.

4. bTB transmission

Patterns of direct and indirect contact between cattle and badgers naturally infected with tuberculosis, Drewe et al. 2013

This study looked at how bTB might be transmitted between badgers and cattle.  It found that direct contact between badgers and cattle at pasture, often thought to be the main route of transmission, was actually very rare. 


A dynamic model of bovine tuberculosis spread and control in Great Britain, Brooks-Pollock, Roberts & Keeling 2014

The first national-scale model of how bTB spreads found that more rigorous cattle measures (improved testing; culling all cattle on infected farms; and cattle vaccination) would be the most effective strategy to tackle bTB - but that even an effective badger cull would fail to halt the spread of disease.

More information from the University of Warwick.  
 

5. Biosecurity

Effectiveness of biosecurity measures in preventing badger visits to farm buildings, Judge et al. 2011

This study found that simple exclusion measures (sheet metal gates, fencing and feed bins) were 100% effective in preventing badger entry into farm buildings, as long as they were appropriately deployed.  Furthermore, the installation of exclusion measures also reduced the level of badger visits to the rest of the farmyard.  

6. Badger vaccination

BCG vaccination reduces risk of Tuberculosis infection in vaccinated badgers and unvaccinated badger cubs, Carter et al. 2012

Vaccination of badgers with BCG appears to be beneficial in at least two ways

This paper states that:

"Vaccination of badgers with BCG appears to be beneficial in at least two ways: by directly reducing the TB burden in vaccinated individuals and by indirectly reducing the risk of unvaccinated cubs acquiring infection, most likely through a herd immunity effect on this susceptible component of the badger population.  Indirect ‘protection’ bestowed upon juveniles before they become accessible for vaccination themselves could be an important contribution to the success of vaccinating wildlife."

BCG vaccination reduces the severity and progression of tuberculosis in badgers, Chambers et al. 2010

"In a clinical field study, BCG vaccination of free-living badgers reduced the incidence of positive serological [bTB] test results by 73.8 per cent. In common with other species, BCG did not appear to prevent infection of badgers subjected to experimental challenge, but did significantly reduce the overall disease burden. BCG vaccination of badgers could comprise an important component of a comprehensive programme of measures to control bovine TB in cattle."

Gloucestershire Wildlife Trust badger vaccine deployment

In 2010 Gloucestershire Wildlife Trust decided that it would be the first organisation to deploy privately the bTB badger vaccine on a selection of its nature reserves in 2011 using its own staff. 

The reports from the first and second years of Gloucestershire Wildlife Trust's pioneering five-year badger vaccination programme (2011 and 2012) are available to download below.

Find out more about the vaccination programme here.

7. Badger predation on ground nesting birds

Not related to strategies to control bTB in cattle but the impact of badger predation on ground nesting birds is often brought into the debate around badger culling, where it is used, mistakenly, as an example of a positive side effect to culling badgers. The effect of badgers on ground nesting birds is well summarised in the New Naturalist on Badgers by T.Roper which looks at the evidence of the two main studies:

Hounsome, T. and Delahay, R. (2005) Birds in the diet of the Eurasian badger: a review and meta-analysis Mammal review 35 199 - 209 

This study reviewed 110 studies of badger diet. Birds were present in the majority but at low levels of occurance (6%). Most reports involve game or ground nesting birds and do involve predation of eggs or chicks. They can potentially be locally significant predators during the breeding season but are opportunist feeders.

Gibbons et al (2007) RSPB Research Report No. 23:56

This study found that badgers don't constitute a threat to any bird species at national or international level and are not economically significant predators of game birds.

Downloads

FilenameFile size
Godfray et al 2013 - A restatement of the natural science evidence base.pdf4.61 MB
RBCT conclusions - ISG report 2007 - bTB the scientific evidence.pdf2.5 MB
Jenkins et al 2010 - The duration of the effects of culling.pdf277.52 KB
TWT perturbation diagram.pdf3.16 MB
Drewe et al 2013 - Patterns of direct and indirect contact between cattle and badgers.pdf321.78 KB
Judge et al 2011 - Effectiveness of biosecurity measures preventing badger visits.pdf256.05 KB
Carter et al 2012 - BCG vaccination reduces risk of TB infection.pdf217.69 KB
Chambers et al 2010 - BCG vaccination reduces severity and progression of TB in badgers.pdf317.37 KB
Gloucestershire Wildlife Trust 2011 vaccination report.pdf826.73 KB
Gloucestershire Wildlife Trust 2012 vaccination report.pdf2.51 MB
RSPB Research Report Predation of Wild Birds.pdf793.26 KB