NEW DELHI: Indian scientists have carried out vasectomies on scores of cross-bred lions, the results of experiments to create new sub-species, to let them die out in a "controlled extinction".

All 300 captive animals, a mix of Asian and African lions many of whom are deformed and diseased, are expected to be dead by 2008, scientists said. "The law of the land does not allow for mercy killing or culling," said Bipul Chakravarty, a senior scientist of India's Central Zoo Authority which devised the programme.

Indian authorities say the animals were cross-bred until 1992 in free-for-all experiments, weakening the genetic pool of Indian cats. The experiments even extended to mating lions with tigers.

"Until we made guidelines 12 years ago, some were experimenting, producing 'Tigons' by mating tigers with lionesses and 'Litigons' by crossing lions with tigresses. None of these are now living," the wildlife scientist said.

As problems of cross-breeding became apparent, "Zoos with hybrids were asked to take population control measures as these animals have no conservation value at all," the wildlife scientist said.

The national zoo watchdog sterilised all its 300 hybrid outcasts between 1999 and 2001 to ensure no new so-called "cocktail lions" were born, and stepped up a campaign for captive breeding of India's pure Asiatic lions.

"Most of these cocktail lions are adults and we're looking at another four years for the stock to end but we're not denying them any animal welfare facilities. They will die a natural death," Chakravarty said.

Zoo authorities have evolved stringent laws on mating at India's 161 state-run zoos and safari parks as part of the national cleanup of animal gene banks. Officials at the Ministry of Environment and Wildlife said the process was being kept under a microscope.

"It may sound politically incorrect but it's a controlled extinction programme to set right the chaos that occurred in the 1980s when African lions rescued from circuses mixed with the Asiatic cats in our zoos," a senior ministry official said.

The cocktail lions have lower immunity and are prone to disease. Many are in a poor physical state with dull coats and thin manes, suffering from a variety of ailments caused by inbreeding.

But in the early years, the genetic problems of the crossed species did not show up, and many were bred so there would be more cats available for exhibition at zoos and safari parks.

Chatbir Park, near the northern city of Chandigarh, holds 30 hybrid lions which belong to an original litter of an unhealthy pride produced by African lions mating with Asiatic types, ministry officials said.

"Their population increased manifold especially in Chatbir so we asked Central Zoo Authority to take action to prevent proliferation of the hybrids," Chakravarty said. Chatbir Zoo was at the centre of a key breeding programme.

"Now we're waiting for them to die out so we can replace them with pure Asiatic stock," Chakravarty said of the zoo, where many of the diseased lions can barely let out a growl, let alone lead a charge.

There are 131 pure-bred Asiatic lions in 58 zoos and national safaris -- their number having swollen by 50 in the past decade because of an accelerated captive breeding programme, Central Zoo Authority officials said. -AFP