This will render many existing slaps obsolete. However replacement universal slapper plates capable of handling six digits are available for around 316, says specialist supplier Edward Holt ('Old slappers still have their uses' Pig World, May).

'Our favoured outcome would have been for producers to be able to register and keep their existing slapmarks,' said NPA regional manager Ian Campbell.

'But we were pretty sure Defra would in the end prefer their own six-digit code; our only success is to ensure the code is alphanumeric which will make for less confusion on the slaughter line than their first choice all-numeric idea.'

Defra's decision means abattoirs are in for a treat: the amount of squinting, guessing and mind-reading they have to do should be markedly reduced as the majority of producers have no option but to buy new - readable - slapper plates.

Sows going for slaughter will also have to be slapped and a separate, larger and tougher slapmarker may be required for this. But Ian Campbell wonders whether this issue could be resolved by slapping gilts as they arrive on pig units.

When To Slap:

In the mid-90s Edward Holt carried out trials with MAFF and the Northern Ireland department of agriculture to determine that pigs can be successfully slapped from ten weeks and the mark still be perfectly legible at slaughter. If a 10mm character size is used at ten weeks, this will grow to 15mm by slaughterweight. Slapping pigs before ten weeks does not achieve a permanent mark. It is possible to have a legible slap of up to two rows of five characters.

The important thing to bear in mind when slapping pigs is that the two hundredth slap should be as clear as the first. Consider synthetic slapper tattoo ink rather than ink that may contain animal-derived products of unknown origin.