A Danish zoo that received death threats after euthanizing and dismembering a healthy giraffe in front of a live audience last month is at the center of another controversy this week.

CNN reports that the Copenhagen Zoo killed four lions to make way for a new male lion brought into the facility.

A statement on the zoo’s website said the killings were necessary to prevent inbreeding, after efforts to move the animals to another facility proved unsuccessful:

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The change in the lion pride had to happen now because Copenhagen Zoo currently has two young females from the 2012 litter and it is ideal to keep these as part of the new pride and then find a suitable male. If the Zoo had not made the change in the pride now then we would have risked that the old male would mate with these two females - his own offspring - and thereby give rise to inbreeding.

Furthermore we couldn't risk that the male lion mated with the old female as she was too old to be mated with again due to the fact that she would have difficulties with birth and parental care of another litter.

In addition the following factors had to be taken into account:

* A new male could not be accepted into the pride as long as the old male was still part of the pride. The younger male would be killed by the older male.

* A new male could not be accepted into the pride as long as the old female was part of the pride. She would kill the younger male.

* A new male in a pride would kill all sexually immature young.

* It's important that a new male lion arrives quickly after the old male is gone. Otherwise the Zoo risks that the females will gang up against a new male and kill him.

National Geographic reports that such killings do not take place in U.S. zoos accredited by the Association of Zoos and Aquariums. The European Association of Zoos and Aquaria noted in a statement that the zoo “had not broken any of its codes of conduct.”

That acknowledgement hasn’t done much to quell the controversy—as of Thursday, a Facebook page titled “Close Copenhagen Zoo” had over 37,000 likes.