Denmark zoo asks people to donate their small pets as food for captive predators

>The Aalborg zoo said it is trying to mimic the natural food chain of the animals housed there “for the sake of both animal welfare and professional integrity” and offers assurances the pets will be “gently euthanized” by trained staff.

I assumed they were going to allow the predators to hunt the animals, but I guess not. I don't quite get what is natural about feeding them an already dead animals, vs say ... feeding them dead animals like normally?