On average, chimpanzees has lifespan of some 40 years. Rita is well past that age.

Fifty-nine-year-old Rita, India's oldest chimpanzee and an inmate of the Delhi zoo, is fighting old age-related health problems and has been put on a liquid diet, officials said on Thursday.

Born on December 12, 1960, in Amsterdam Zoo and acquired by the Delhi zoo in 1990, Rita is the oldest chimp in India and probably the "oldest in Asia", according to the Limca Book of Records.

On average, a chimpanzee has a lifespan of around 40 years. Rita is well past that age, according to zoo officials.

"Rita has not been keeping well since July 27. It seems age has finally caught up with her. She has not been eating properly and grown frail. She doesn't move around much," a Delhi zoo official said.

"We are providing her vitamins, minerals, liver tonic and iron supplement syrup regularly. Since July 27, she on a diet of juice, coconut water and milk with ground almonds and walnuts," Delhi zoo's curator Riyaz Khan said.

"We have also provided her mattress and a TV to watch videos," he said. A team of experts from the Indian Veterinary Institute in Bareilly is treating the chimp.

"On Thursday, Utkarsh Shukla, the deputy director of the Lucknow zoo, visited the chimpanzee and suggested the line of treatment. A three-member team constituted by the Central Zoo Authority also took stock of her health," another official said.