Copenhagen Zoo's decision to kill Marius - an 18 month old healthy giraffe - and to perform a public autopsy in front of children sparked a global outcry. Despite receiving numerous death threats and hate emails, the zoo's scientific director insisted he had no choice but to kill Marius because there were already too many giraffes with similar genes in the European breeding programme.

Reporter Hannah Barnes travels to Denmark to explore the reasons behind the killing of Marius and other healthy animals. Back in Britain she talks to staff at British zoos to find out whether what the Danes did in public is happening behind the closed doors in the UK.

Producer: Anna Meisel.