The January 2013 European Union partial sow stall ban allows European Union producers to keep sows in stalls for four weeks, but in the Netherlands the allowed period is only four days.

According to Press reports a large number of Dutch producers have signed a petition against the four-day rule, and the farming minister is being challenged on the issue in the Netherlands House of Commons.

Wageningen University has been asked to support the debate with scientific facts and figures and has contacted NPA for its views.

The four weeks allowed in stalls during embryo implantation gives most continental producers a significant advantage.

NPA's Dr Peter Cottney points out that some producers and genetics specialists in Britain see the use of stalls—particularly during the implantation period—as accounting for much of the difference between average British indoor production of 22.9 pigs per sow per year and the European Union average of 24 pigs per sow per year.

The United Kingdom, Sweden and Luxembourg don't allow stalls under any circumstances.

From 2015, Danish pig producers with new housing will come into line with British pig-keepers—their sows will no longer be allowed in stalls for up to four weeks, as permitted under European Union law.

But producers with existing sow housing have more than two decades to comply with the new Danish legislation. They won't need to get rid of their stalls until 2035.

By exceeding the requirements of the European Union partial stalls ban—albeit over a period of 21 years—the Danes could be sacrificing around one pig a litter, according to some British producers.