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Bovine TB
Bovine TB in the pilot badger cull zone in Gloucestershire
  1. Paul Torgerson
  1. University of Zurich, Section of Epidemiology, Vetsuisse Faculty, Winterthurerstrasse, 8057 Zurich, Switzerland
  1. e-mail: paul.torgerson{at}access.uzh.ch

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IN their recent letter (VR, May 16, 2015, vol 176, pp 527-528) Mr Blowey and others correctly observe that there has been a decrease in the number of total reactors in the western region of England from 2013 to 2014. They also observed that in the badger cull areas of Gloucestershire, Hereford/Worcester and Somerset the decrease is considerable and they mused over the coincidence that these are in the cull zones. They conclude by speculating that not only has the cull not led to an increase in bovine TB, but indeed rather the opposite.

When making such speculative statements, it is essential to not look at two years of data in isolation. The trend, before the pilot badger culls were implemented, was for a decreasing number of reactors (Table 1). In the western region, between 2008 and 2013, the number of reactors decreased from 20,725 to 17,822, without the help of badger culls. In Gloucestershire, for example, it decreased from 2433 to 1622. Also within these data, between successive years, there is a huge amount of variability. For example, between 2009 and 2010 the numbers of reactors decreased in Gloucestershire from 2268 to 1604 – a decrease of 664 when there was no badger cull. On the other hand, the decrease in reactors between 2013 and 2014 that Mr Blowey and others imply may be due to the cull is just 469. Somerset on the other hand has had reactor numbers bouncing around between a minimum of 1235 in 2009 and a maximum of 2389 in 2013, with no evidence of any trend either up or down regardless of badger culls. Indeed the drop to 1576 in 2014 may only be a case of reverting to the mean values seen between 2008 and 2012, with 2013 being an exceptionally high year. The only conclusion that can be drawn is from the total western regional data. Here, there appears to have been a modest decline in the numbers of reactors between 2008 and 2014 and this started well before the pilot badger culls were implemented. Also within this decline there is sizeable variability from year to year in individual counties. Hence it is far too premature to conclude that there is any correlation of reactor numbers with the presence or absence of the pilot culls, much less causality. It is essential to ensure that data are rigorously analysed and put into context before trumpeting the success or otherwise of a programme that has serious environmental, welfare and cost implications.

TABLE 1:

Number of reactors slaughtered by county 2008 to 2014 (Defra 2015)

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