ANY reader who decided to check the figures I quoted last week on the number of cattle slaughtered in Devon under bovine TB control measures may have noticed that I had misread the 2010 figure on Defra's website.

The figure I quoted was 6,781, whereas it should have been 5,761.

This means that the drop between 2008 and 2010 in the number of cattle slaughtered per year was even greater than I said – a decline of 20 per cent, fairly close to the 22 per cent decline in the western region as a whole.

The Defra statistics show the big hike in TB cases resulting from the restocking that followed the Foot and Mouth (FMD) disease outbreak in 2001, and also that the increase in cattle slaughtered since then has been mostly a function of the number tested.

The latter has risen steadily since 1998, apparently reflecting a rise in average herd size and in the total number of cattle in the region.

In fact the number of reactors slaughtered, expressed as a proportion of the total number of tests carried out in each year, increased rather slightly between 2002 and 2008 (the last year for which the total numbers of cattle tests are quoted), from 49 to 71 per 10,000 tests in Devon, whilst the rise in the western region as a whole was negligible, from 63 to 65 reactors per 10,000 tests.

By contrast, the proportion of conclusive reactors more than doubled between 2000 and 2002 (i.e. before and after FMD), both in Devon and in the western region as a whole.

Unless the total number of cattle in the region has declined quite significantly over the last two years (the number of herds tested has changed little), the drop in the number of cattle slaughtered presumably means there has also been a significant fall in the proportion of TB reactors.

None of this means that TB is not a very serious problem, which it is, nor that badgers don't spread TB, which they do. But if we are going to have the calm, measured debate that MP Neil Parish called for in last week's Word from Westminster we need to be clear about the trends already in train before the badger cull commences.

You can find statistics on the number of cattle slaughtered between 1998 and 2010 by region and county in England, Wales and Scotland at the following web address: http://www.defra.gov.uk/statistics/files/defra-stats-foodfarm-landuselivestock-tb-county-animals-1107071.pdf.

FRANCIS KIRKHAM Nymet Rowland Crediton