A Shetland pony had to be put down after being stabbed and slashed numerous times in what the RSPCA says was a deliberate attack.
The pony, Murphy, was in "an awful state" and "very distressed, as you'd expect", said RSPCA inspector Terri Ann Fannon.
Emergency services called the animal welfare group to Downhill Road Allotments in Sunderland at about 1am on Friday following a suspected arson attack in which another horse died.
Murphy had "numerous slash and stab injuries all over his body", Ms Fannon said.
She added: "One stab wound on his back left knee was so deep the damage was irreparable.
"Very sadly the vet decided that there was no other option but to put him to sleep."
It is not known how old the appaloosa Shetland stallion was.
The RSPCA said it had not established who owned Murphy, despite there being a number of people at the scene.
The charity, which has launched an investigation, is urging the owner and anyone who has information to get in touch.
"Clearly this was a deliberate attack," said RSPCA inspector Trevor Walker.
"It's absolutely shocking that someone would do something like this."