A piece of the giraffe Marius is seen hung up in a cage occupied by primates at Copenhagen Zoo. Thomas ekfeldt

Copenhagen Zoo euthanised four healthy lions on Monday just a few weeks after putting down and publicly dissecting a young giraffe, causing outrage among animal lovers around the world.

The zoo said it had killed a 16-year old male lion, a lioness of around the same age and two younger females after a new male lion arrived on Sunday as part of a programme to renew the zoo's breeding stock.

"Now two young females born in 2012 have become mature and are healthy, they can take over from the old female and form a strong triangle with the new male," the zoo said in a statement.

It said the two young lions were not old enough to fend for themselves and would have been killed by the new male as soon as he got the chance.

Copenhagen Zoo was the subject of widespread criticism in February when it put down Marius, an 18-month-old giraffe, and dissected it front of school children. The animal was killed to avoid in-breeding, it said.

Staff received death threats after the healthy giraffe was killed. The zoo's head, Steffen Straede, said he did not expect the same reaction this time.

"I think people are more enlightened after Marius," he told the Ritzau news agency.

The lions' body parts will be used for research.

Reuters