Daily Mail.

A horse believed to be the oldest in the world has died after reaching the age of 51. Shayne, a liver chestnut Irish Draught cross thoroughbred, had been enjoying a comfortable retirement at an Essex sanctuary in Great Britain, spending up to five hours a day in the fresh air despite suffering from mild arthritis. But last month he was unable to get back up after his legs gave way and staff took the decision to put him down.

The previous title of oldest living horse in the world was held by Welsh/Arab steed Badger, from Pembrokeshire, Wales, who died aged 51, in in 2004.
Last year, the Guinness World Records team said nobody had laid claim to the title since Badger’s death. Staff at the sanctuary believed him to be 51 based on the date of birth given by his previous owner, and medical checks.