Both Copenhagen zoo and Odense zoo has killed healthy animals despite hundreds of thousands of voices against. Both these zoos are following breeding programmes set by the European Association of Zoos and Aquaria (EAZA) which results in "surplus" animals. EU and EAZA needs to change the rules so there will no longer be healthy "surplus" animals being killed.
For more information on zoos and animals in captivity check out the Born Free Foundation: http://www.bornfree.org.uk
Also, check out OASA (www.oasa-dk.dk) who was the first Danish welfare organisation to condemn the killing of healthy animals in zoos and who calls for a ban of this procedure.