Shock-horror, as a Copenhagen zoo kills a giraffe and feeds it to the lions (Warning - picture of dead giraffe in this link) an article tells us that European zoos kill lots of animals every year.
Well, of course they do. That's the thing about those slow-moving herbivores, not especially endangered, that they keep in herds. If they breed, they have 50% bulls/males/cobs/bucks/dogs and 50% cows/females/pens/harts/bitches. But, especially in herd animals, you don't need that many males. Like Russell Brand at a not-very-bright-women's convention, one male can cover a lot of females. Leaving lots spare.
And yes, you could leave the poor old souls wandering around castrated. But let's face it, if you don't feed lions with spare giraffes, bison, wildebeests and penguins, you only have to feed them dead cattle, sheep etc. Lions eat meat. It's a fact.
Strikes me there's two ways to look at this. We either accept that we keep lions, tigers, cheetahs etc in zoos until the point in the future when somehow we can guarantee they'll be OK to survive as species in the wild, and we believe that the unnatural situations in which we keep zoo animals is justified by protection of biodiversity and/or the educational and/or entertainment value of these creatures.
OR we decide that zoos are so bad, we should close them all and just leave wild animals to whatever protection we can give them in the wild.
But the argument that you can't feed a giraffe to lions because it's gangly, endearing and spotty doesn't hold water. To us, it may seem that cute Marius the giraffe is more worthy of life than a clapped-out Friesian cow. But to a lion, they're both lunch. Spots do not make you more worthy of life.