"There are things we know we know. We also know there are known unknowns. That is to say we know there are some things we do not know. But there are also unknown unknowns - the ones we don't know we don't know."
This quote from US secretary of defence Donald Rumsfeld sums up the worries of some British pig producers about live pigs being brought into the country. European rules ensure live pigs entering Britain are clean and healthy, but how are they to be tested for the diseases that we don't even know we don't know about?
There is an increasing flow of live breeding animals from mainland Europe. Over recent years there has been a progression from importing frozen semen to, this year, the import of commercial boars, and - so it is being claimed - gilts for complete restocks.
Tightly policed imports of genetics are one thing, but fears are now being expressed that this trend could threaten Britain's biosecurity because of the diseases we don't know about and the diseases we don't even know we don't know about.
A biosecurity campaign by genetics company chairman Stephen Curtis will be launched next week with the first of a series of full page advertisements in Pig World.
Stephen Curtis argues that importing live pigs and semen puts the whole British industry at risk. In his campaign, he will be urging producers to support a self-imposed cordon sanitaire. He says he will be calling on NPA and BPEX for support.
"In principle I support the concept of his cordon sanitaire," said NPA regional manager Ian Campbell today, "but I do so in the knowledge that - in my view - to realistically apply this across the genetic spectrum is now no longer possible.
"One of the principal worries in the late 90s was that the infrastructure of our industry could be permanently damaged as the British pig population slumped and now that worry can be seen as having come to pass.
"The inability to trade effectively during swine fever and foot and mouth, coming on top of a weak home market, was financially extremely severe for our breeding companies and a key reason for nucleus breeding populations to be based in this country, security of health, had evaporated.
"Against that background, it would be wrong to discriminate against genetic material exchanged within company across the water where the risks can be quantified and benefits judged.
"Certainly it still represents a risk if we accept that PRRS and PMWS probably needed a porcine host to manifest themselves in our herds but it is the sort of risk that breeders over the years have taken in closed herds where the only genetic import is semen.
"The danger I see is that we are becoming relaxed about this transfer of material and have taken the next step to bringing live animals into commercial herds. In 2005 if Aujeszky's is eradicated in Holland, we will certainly find Dutch traders offering competitively priced weaners to British finishers.
"The Dutch are great traders and will almost certainly be extending their trading activities into Eastern Europe bringing live pigs and meat across borders to process in Dutch factories. Notifiable viruses such as classical swine fever are of course a concern but what worries me most is the activity of insidious new viruses that ease their way from east to west and, like PRRS and PMWS, and take years before they are identified. Once upon a time any of these were pulled up with a bump when they hit that strip of water around us.
"I totally support the national drive to regain our high health status and believe we must be very cautious in taking porcine material into this country. The Danes erect very strong barriers to protect themselves and they don't have the geographical good luck that we do."
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