SHANGHAI (AFP) – The next time you bite into your favourite donkey burger beware – it might actually be horse, pig or even mule meat. That is the warning from authorities in China after a media investigation revealed that some butchers in a city famed for its donkey burgers had engaged in a nefarious plot to substitute donkey with cheaper meats. Restaurants all over China, but mainly in Beijing, bought the fake donkey meat, the state Xinhua news agency and other Chinese media said. Underlining the severity of the problem, authorities in the northern city of Hejian called an emergency meeting on Monday and launched an investigation. Officials there vowed to punish those producing the dodgy donkey meat.