Key Points:

Eight months after staff developed a unique plan for his care, Auckland Zoo's blind rhino Mandhla has had to be put down.

Staff were forced to euthanise the 28-year-old, 2000kg animal yesterday after it suffered a prolapsed penis, which left it incapable of urinating.

An autopsy was carried out yesterday afternoon to confirm the cause of the prolapse. Zoo team leader Michael Batty told the Herald Mandhla may have suffered a clot, stroke or seizure, all of which could be caused by the neurological condition that made him go blind in November.

Results of brain tissue tests are expected in a few days. While staff were able to catheterise Mandhla under anaesthetic, to help relieve his bladder, by yesterday morning his condition was clearly irreversible, zoo vet Dr John Potter said.

"This problem would have been caused by a worsening of this same neurological problem, and we all felt that it was in Mandhla's best interests to humanely put him to sleep."

Mandhla - who was born in San Diego Zoo in 1979 - had lived in New Zealand since he was one, and was "very, very popular" with zoo workers and visitors, Mr Batty said.

"He's certainly an individual, he's not just another rhino."

Mandhla made headlines last month after zoo staff used sound and smell prompts to help him cope with being blind.

Mr Batty and his team devised voice commands and scent trails to help Mandhla trace a safe route round his area. The keepers made noises with their feet, jingled keys or shook the food bucket so Mandhla could hear them coming quite clearly and not take fright.

Rhinos generally live to about 40 years old, meaning Mandhla was only in middle age, but "his number has come up now", Mr Batty said.

Auckland Zoo has another three rhinos recently arrived from Hamilton Zoo, and there are no plans to replace Mandhla.