A cocker spaniel puppy was left with severe wounds thought to have been caused by being fitted with a collar that was too small.
Guinness had a cut to his neck when he was found abandoned in Grays, Essex in October.
Insp Joe White, of the RSPCA, said: "I could not believe it - it was one of the worst wounds I have seen in my whole time as an RSPCA inspector."
The dog has now been rehomed with a new family after emergency treatment.
"It looked as though he had been left with a collar on that was far too small for him and it had cut into his neck," said Insp White.
"I have seen some awful things but this one really hit me.
Warning: Graphic image below
"How anyone could neglect this poor puppy in this way and ignore such an awful wound that so obviously needed treatment is just beyond me."
His new owner, Charlie Rees-Brown, from Grays, said: "The minute he walked through the door I just knew that he wasn't going to be leaving the house.
"He is such a cheeky, happy boy you really wouldn't know he had been through something so awful."
Guinness' original owners were never traced.