If estimates that Rosie is aged 54 are correct, she could be on the verge of becoming the oldest donkey in the world. Proving a donkey's age is difficult – although estimates can be made by looking at the animal's teeth.
Ms Manger, who runs Kenstud Pony Rescue, at Dalley Farm, where Rosie lives, said: "We don't have an exact date of birth for her, but talking to people who have owned her over the years, she should be about 54.
"Her teeth have ground right down through eating and a dentist who looked at her said she'd be about that old."
But Rosie is still in a remarkably good condition.Farm volunteer Mel Grace, 67, said: "I go to see her every morning and she goes out into the field for a little run."I have no idea why she's lived to such an age. She's clearly been well fed and has lived a happy life. "Why do some people live to 100 and others don't? Maybe it's just in the genes."
Mr Grace has helped look after Rosie at the farm for the past 18 months. He said: "Rosie is very affectionate – it's been an extremely rewarding time."Rosie came to the farm in 2006, when Ms Manger agreed to care for her on behalf of her previous owner, who was an elderly woman.
She also agreed to take care of a second donkey, Toby, who had been Rosie's companion for 40 years.
When Toby died last year, Ms Manger said she considered having Rosie put to sleep to spare her any grief.
"Donkeys are like swans – they pal up with a friend for life and when one of the pair dies, the kindest thing in some cases is to put the surviving one to sleep," she said.
However, having become extremely fond of Rosie, Ms Manger decided to match Rosie with Arabian pony Gemma, to see if the pair bonded. It proved to be the right decision as Rosie is now inseparable from Gemma and has got over the heartache of losing Toby.
A spokesman for Guinness World Records said Ms Manger would have to prove Rosie's age for the donkey to be entered into the record books. He said: "The record for the oldest documented age for a donkey belongs to Suzy, who lived in Glenwood, New Mexico and reached 54 years old in 2002."
But Ms Manger said she was doubtful of being able to get the donkey's age verified because she does not have her birth certificate.