According to Edward Holt from slap marker technology manufacturer, Id and Trace, the slap marking system that tattoos a six- or seven-digit herd number on the shoulders of the pigs when it leaves the farm has an advantage over ear tags because the marks are easier to read and they are not lost during the dehairing process on the slaughter line, as can be the case with tags.

The slap mark is also considerably cheaper than the tag and as it stays with the carcase after slaughter and through the splitting process into the chiller, it allows batch traceability and identification right through to primal cuts and beyond.

The only problem that can occur with a slap mark is its legibility, Mr Holt said.

"Some 24 per cent of slap marks can be illegible," he said.

This is largely caused through poor equipment and poor technique in delivering the mark.

Mr Holt said that research had shown that by giving the slap marker a profiled handle as seen with an axe or a racket from a racket sport, the operator can deliver the mark more easily and clearly, hitting the correct spot on the pig's shoulder.

The operator also has to ensure that the needle density is correct and the head is clean and sharp to give a clear mark.

Mr Holt said that while many abattoirs use different systems for tracking and tracing, the use of a slap mark helps to give a virtually failsafe method of batch identification.

He said that the best weight to use the slap marker on the pigs is when they reach 50kg although some pigs will have to be marked earlier if they are moved off the farm at around 30kg for finishing.

He added that if sows and boars are moved off the farm too, then the equipment has to be accurate and robust enough to be able to mark the older animals with a tougher skin.

Mr Holt said that the regulations that required every pig leaving the farm of origin for slaughter to be identified opened the flood gates for equipment from around the world to be imported.

However, the research carried out by Id and Trace through the 1980's, 90's and in 2008 revealed that pigs and farming requirements had changed and the equipment had to be developed to meet the new requirements.

Trials also showed improvements on slap score in the abattoir giving results of excellent, good and fair giving good assurance.

The company had also developed food grade ink for the slap marking. At present, there are no regulations that require the marking to be with food grade ink.

The food grade ink that has been developed by Id and Trace was introduced following a request from the UK pig meat processor, Cranswick.

To order your Id and Trace slap markers, please click here.