How many healthy animals do zoos put down?

When Copenhagen Zoo put down a healthy male giraffe earlier this month, much of the world was horrified. But those in the know say it's quite normal - a fate that befalls thousands of zoo animals across Europe every year. That figure includes some smaller animals, not just the big "charismatic megafauna" that have the potential to make headline news. At the larger end of the scale, Copenhagen Zoo has put down leopards, tigers, lions, bears, antelopes and hippos in recent years, as well as the young giraffe, Marius.