We have a number of approaches. We do some roadkill surveillance in areas to identify where there is disease. Also, whenever we have a breakdown on a farm, an assessment is carried out by APHA vets to try to establish the most likely cause of that breakdown. So there are breakdown epidemiological reports.
The hon. Lady also raised an issue about herd size. In addition to the point made by my hon. Friend the Member for North Herefordshire (Bill Wiggin), the fact of the matter is that it is an epidemiological reality that the more cattle there are in a herd, the more interfaces there are with the environment and the more likely they are to pick up infection. I remember that some years ago our chief scientist in the Department for Environment, Food and Rural Affairs got very excited and thought that those with small herds must be doing something right. However, we concluded that it is simply a mathematical fact that a small herd has fewer interfaces with the badger population and therefore has a lower propensity to have a breakdown.
My hon. Friend the Member for Chatham and Aylesford (Tracey Crouch) raised an important issue about slurry. I can tell her that I have had meetings with Dick Sibley and that he has attended roundtable discussions we have had on this issue. However, as long ago as 2015 we launched a biosecurity plan that included slurry management best practice guidance, so this is an issue that we recognise and that we try to improve. The evidence is a little mixed, because the reality is that if we are testing and removing cattle, we would tend to remove them before the disease shows up in slurry, unless the test is ineffective and is missing those cattle. So this is an area that we are keen to look at further and, as I have said, we are in dialogue with Dick Sibley on some of these matters.
My hon. Friend the Member for North Herefordshire made a point about diagnostic tests. He is absolutely right—we are now allowing the use of unvalidated tests and, again, Dick Sibley is using one of those tests. We have also dramatically increased our deployment of the more sensitive interferon gamma test.
My right hon. Friend the Member for North Shropshire made an important point about epidemiology and, crucially, how we get daughter infection below one, so
that we can put this disease into permanent retreat. The R0—the reproductive number that he mentioned—is notoriously difficult to calculate, but we have a track record in our own history of taking this disease from a very high prevalence in the 1930s down to zero in the 1980s. So there is a point whereby, if we keep going, we can put this disease into permanent retreat.