British police and animal welfare authorities rescued 84 neglected horses Wednesday from a farm where they had found 31 dead horses, ponies and donkeys, officials said.

Royal Society for the Prevention of Cruelty to Animals officials were called to the farm in Amersham, 35 miles west of London, on Friday, the RSPCA said in a statement.

It did not elaborate on how the horses died, saying it could not give further details due to possible prosecution.

A 44-year-old man was arrested for allegedly assaulting a police officer and causing criminal damage, Thames Valley Police said.

Three horses had to be euthanized immediately because they were suffering so badly and 14 others were immediately taken away, RSPCA Chief Inspector Rob Skinner said.

"The operation is going on at the moment and we're discovering further possible offenses," Skinner said on Sky News.

Police and staff from the Redwings Horse Sanctuary helped remove the remaining 84 horses, who were taken to sanctuaries run by Redwings and the International League for the Protection of Horses.

Redwings spokeswoman Nicola Markwell said the operation was the largest one-day rescue operation her organization had ever conducted.

"Redwings are hopeful that a prosecution of the owner will follow — for both the deceased equines and those surviving that were considered to be in an unacceptable condition — but it is too early to comment on this in full," Markwell said.