According to Ms Hammerling these animals were slaughtered. She said the systematic "overproduction of animals" at zoos, designed to attract more visitors, was to blame. Ms Hammerling said she also knew of several tigers and leopards from Berlin that ended up in a tiger breeding farm in China that promoted itself as a purveyor of traditional potency-boosting medicines made from big cats. She alleges the animals' remains were turned into drugs.

Mr Blaszkiewitz, who became something of a personality after the polar bear Knut was born at his zoo in December 2006, strongly denies the charges. The bear's popularity bumped up visitor numbers and profitability. Responsible for 23,000 animals and credited with turning the Berlin zoo into the city's most popular attraction, Mr Blaszkiewitz believes his detractors are spreading "untruths, half-truths and lies". "The stories of slaughter have been invented. We only work with respectable zoo dealers," he said.

He added that while animals were sent to China in the 1990s, their transfer was approved by the federal office for nature protection. Rearing animals was central to his work and visitors should have the chance to observe the rearing process, he said. He denied claims that money making was the motivating factor.

However, at Nuremberg zoo, the deputy director, Helmut Magdefrau, has been reported as saying: "If we cannot find good homes for the animals, we kill them and use them as feed." At Nuremberg recently an antelope was fed to caged lions as visitors watched in outrage. A spokeswoman for Ms Hammerling said the MP was prepared to press charges over the Berlin zoo.

Prosecutors will soon announce whether the case goes to court. The zoo has been unable to shake off the charge that it has been encouraging animal births to boost visitors keen on "cute offspring". The phenomenon has been labelled "Knut-mania", after the cub became one of the biggest moneyspinning animals in history, thanks largely to marketing offshoots. Knut products now range from cuddly toys to credit cards. The Nuremberg zoo now has its own celebrity polar bear cub, Flocke, which ventured outdoors for the first time on Thursday.

■ The Australian black swan Petra, which made headlines by falling in love with a swan-shaped pedal boat, had been building a nest at Muenster zoo with a white swan called Bruce. But zoo officials say Bruce has now left Petra - so they are planning to reunite her with the pedal boat. Guardian News & Media, Australian Associated Press, Associated Press