Irresponsible breeding has led to a rise in the number of abandoned Staffordshire bull terriers, a dog rehoming home charity has said.
The City Dogs Home in Stoke-on-Trent said the breed accounted for about half of the dogs left with it.
It said the dogs had often been trained to be aggressive.
The Staffordshire Bull Terrier Club (SBTC) said the breed's reputation had been damaged by people cross-breeding them with banned pit bull terriers.
Dogs home manager Vicky Philips said: "People are breeding dogs not knowing what they have got, they could be breeding brothers and sisters and God knows what. The outcome is a bad breeding with bad traits.
"They are breeding wrong ones with the wrong ones and it's turning out bad stock. This is what is ruining Staffies."
James Beaufoy, president of the SBTC Kennel Club registered society, said criminals were breeding Staffies with types of dog that had been banned under the Dangerous Dogs Act in order to circumvent the law.
He said: "The Staffie's temperament is bold, fearless and reliable.
"They are a perfect family pet. You could not train a real Staffie to attack a human being because they trust them so much. A pit bull terrier cross is a very different matter though.
"The dogs that gangs use to attack people look nothing like a Staffie, they just call them that to get around the law."