Tests in January had shown animal feed produced by the company in the state of Thuringia contained around 15 times more than the permitted level of dioxin.

Dioxin has been linked to several cancers in humans, including lymphomas and lung cancer.

Some 300 pigs that had been given the feed had to be slaughtered after tests showed high levels of the poison, according to a statement on Thuringia's Agriculture Ministry Web site.

The firm was ordered to halt feed production on January 31 and test its entire production for dioxins, the ministry said. The company was not identified.

"According to test results published today, it cannot be ruled out that feed delivered before January 31 was contaminated with dioxins," it said.

Dioxin comes from both natural and industrial sources, such as medical and municipal waste incineration and paper pulp production. It enters the food chain when animals eat contaminated plants, building up in the fat of mammals and fish.