The authorities in the Netherlands are trying to trace hundreds of pigs that have been exported to several European countries despite having been fed an illegal growth hormone.

A Dutch agriculture ministry spokesman said Germany, Belgium, Spain and Italy had all imported contaminated animals.

More than 40 farms in the Netherlands have been found to be using feed containing the hormone, MPA Medroxyprogesterone-acetate.

The authorities have ordered around 2,000 farms now under investigation to halt the slaughter of pigs for a week.

MPA is banned in the European Union as it is suspected of causing infertility in humans, though it is legal in the United States.

A group representing Dutch farmers, LTO-Nederland, has denied that most farmers knowingly used the substance. A bankrupt Dutch-owned firm in Belgium is being investigated for supplying the contaminated feed.

From the newsroom of the BBC World Service