Copenhagen Zoo has been labelled a "hideous institution" for another killing - this time to make way for a new lion.

First, it was the killing of Marius, the giraffe that caused international outrage, now a family of four lions have been declared surplus to requirements at the vilified zoo to meet its breeding programme ambitions.

The zoo said it was unable to find new homes for the animals and argued that the two lion cubs would have been killed by the new male anyway.

According to Reuters, the lions' body parts will be used for research.

Ben Williamson of the People for the Ethical Treatment of Animals (Peta), said the latest killings confirmed that zoos such as Copenhagen were "hideous institutions that do not deserve public support".

He said: "Copenhagen Zoo, which pleads that there is nowhere to put these animals, didn't find them abandoned on the doorstep one morning – the zoo brought them into this world. Like domesticated cats, big cats breed, unless you make sure that they are sterilised, and that is exactly what the zoo had an ethical obligation to do, rather than bringing cubs into the world simply to bump them off.

"This callous action highlights the fact that zoo breeding programmes serve no conservation purpose, because animals born in zoos are rarely, if ever, returned to their natural homelands. Instead, zoos spend millions on keeping animals on display like living museum exhibits and dispose of them when they become inconvenient or there are "too many" of one kind."

Mirja Holm Thomsen, who founded the Organisation Against the Suffering of Animals, (Oasa), in Copenhagen, said: "We are appalled and disgusted by this. Copenhagen Zoo has killed four healthy animals. It's unethical to breed animals and then kill them as soon as they don't fit into a programme. It shows that Copenhagen Zoo and other zoos have no respect or care for the animals."

Such heartlessness has caused more than 40,000 people to sign a petition to stop the zoo from killing more animals.

Paul Armstrong from the UK wrote: "How long are these murdering scumbags going to be allowed to get away with this. What kind of vets carry out this kind of barbarism. They should hang their heads in shame. What is the Danish government doing to stop this."

"More reason to stop every zoo in all over the world Shame, shame, shame!!!" Meralda Sabatino from Italy said

People look on as a veterinarian prepares to dismember the giraffe Marius after it was killed in Copenhagen Zoo February 9, 2014.
People look on as a veterinarian prepares to dismember the giraffe Marius after it was killed in Copenhagen Zoo February 9, 2014 Reuters

People also took to Twitter to vent their frustration.