A greyhound's ears were cut off before being left to die on a south Wales mountain, a court has heard.
A warrant has been issued for Andrew Gough's arrest
Magistrates in Blackwood found Andrew Gough, 28, guilty of ill-treating the dog in a botched attempt to disguise his identity.
The court heard how he offered to "humanely put down" the dog - called Last Hope - for £10.
Gough was not in court on Monday and a warrant was issued for his arrest. He will be sentenced later.
Magistrates heard that the dog's ears were sliced off because identity tattoos would have led to him being traced.
Prosecuting, Martin Prowel said: "The dog was subjected to quite brutal ill-treatment in a botched attempt to kill it.
"This involved cutting off both ears and striking a severe blow to the forehead which penetrated the skull and damaged the brain."
The court heard the greyhound's owner, John Hurley, had allegedly paid £10 to have the Irish-bred dog destroyed by Gough, a track groundsman.
He had promised that he would "humanely put down" the dog and bury him in lime on a farm.
Instead, the court heard he left the mutilated animal still alive on a mountainside in the Rhymney Valley, south Wales.
He was discovered lying on rubbish with a hole in his forehead on 2 May by a walker, and was later humanely destroyed.
Magistrates were told greyhound lovers had been " appalled" by the animal's suffering and had circulated posters at tracks showing pictures.
Both Last Hope's ears had been cut off
Last Hope had a distinctive white blaze on his chest and people came forward to identify him.
Former trainer Mark Emmett said Last Hope had a toe injury which made him lame, ending his racing career
He was "very aggressive" towards other animals and could not be rehomed as a pet, said Mr Emmett.
"It was decided he should be put down and Gough said he would do it with a humane killer," said Mr Emmett.
The former trainer later challenged Gough about the mutilated dog but he denied it was Last Hope, the court heard.
Gough allegedly told Emmett: "I swear on your children's lives that dog is not Last Hope".
Vet Timothy Ingham said the dog's head wound was probably caused by a bolt gun which had not been properly fired.
After the case, Alain Thomas from the charity Greyhound Rescue Wales estimated that, in Wales alone, between 100 and 300 greyhounds no longer fit for racing were killed every year - though not all in such an horrific way.
"The way that Last Hope spent his last few hours was absolutely shocking," he said.
"This case exposes a culture in greyhound racing where some people treat these dogs as commodities to be disposed of in any way possible.
"I am very pleased that the magistrates have found Andrew Gough guilty. We have got to get to these people, we have got to expose them and get them out of racing."
Sian Edwards from the charity Dogs' Trust added : "I would like to think that those decent people who work in the industry - dog owners, trainers, track owners - could join forces with us to improve dog care in racing."