By Palash Kumar Sun Sep 17, 3:30 AM ET CHANDIGARH, India (Reuters) - Twenty-one lions are dying in a zoo in north India after a cross-breeding experiment to boost the park's attractions went disastrously wrong. In the 1980s officials at the Chhatbir Zoo in the northern city of Chandigarh, bred captive Asiatic lions with a pair of African circus animals, resulting in a hybrid species. Within a few years it became obvious it had not worked. The offspring found it hard to walk, let alone run, because their hind legs were weak. And by the mid 1990s the big cats -- which live for up to 20 years in captivity -- showed symptoms of failing immune systems. But it wasn't until 2000 that the breeding program was ended, and the male lions given vasectomies, by which time the zoo had 70 to 80 such lions. Their number dwindled slowly, with disease killing some and some dying of wounds inflicted by other lions. Authorities say they are waiting for the population to "phase out" before they can start breeding pure Asiatic lions. "But the effort here is to help them die with dignity," said Dharminder Sharma, a senior zoo official. "We give them all the facilities to live a happy life in their last years. Some of the old lions are even given boneless meat." Last year the zoo opened a special enclosure, away from the main exhibit area, where it keeps lions who have become too feeble to defend themselves. It has been dubbed an "old age home" for lions. Ailing Lakshmi and Lajwanti now live in these sheds, which have a small caged courtyard. Both are hybrid and are extremely weak. They can barely stand up or walk. Their only activity is a small but painful walk to eat their meals. However, if challenged, they can still muster a spine-chilling roar. In August, Lakshmi stopped eating. Doctors at the zoo put her on a drip and fed her glucose through water. "Those were nervous times for us," said Sharma. "We tried very hard to keep her alive and eventually succeeded when she slowly started to eat ... Even if they are meant to die, it doesn't meant we kill them by not treating them," he added. Asiatic lions are found only in India and, at present, there are about 300 of them in the Gir national park in the western state of Gujarat. In the mid-20th century, their numbers were less then 15 as they were vigorously hunted by the Maharajas and princes for whom the majestic animal was the most coveted game. The population recovered after a breeding program launched in the Gir sanctuary in the 1960s.