"If you want to make pit bulls and Rottweilers illegal today, give somebody a couple of generations and they'll make German Shepherds into the dog of danger," he said.
Zawistowski, a certified applied animal behaviorist, says if given the choice of six breeds, he could create a dog in ten years that would make drug dealers "pee in their pants."
But he adds it's more than just genetics that determine how a dog behaves. Training and environment also play a part.
"A pit bull that has been properly socialized and trainedand kept in a home, walked on a leash, and kept in a yard with a fenceisn't necessarily dangerous," Zawistowski explained.
On the other hand "a pit bull kept by somebody who facilitates its fighting behavior and its aggressive behavior; fails to control the dog and fails to keep the dog in the yardthat's a dangerous combination," he said.
In 1989 Denver banned ownership of American pit bull terriers, American Staffordshire terriers, and Staffordshire bull terriersthree breeds commonly referred to as pit bulls. Mixes of those dogs are also outlawed.
The ban was put into place as a public safety measure, said City Councilwoman Rosemary Rodriguez, after two separate incidents involving pit bulls where a minister was severely mauled, and a young boy killed.
But in April, a state law passed that stopped Denver from enforcing the ordinance.
The city fought back, filing a lawsuit against the state claiming the new law infringes on its power as a home-rule city.
A decision on the case could be made as early as July, according to the city attorney's office.
"Once that [lawsuit] is resolved we are going to fully discuss whether or not the current law is what we want to maintain, or if we should look toward revising our breed-ban law," Rodriguez said.
None of the city council members who passed the ban more than a decade ago still serves.
Rodriguez said she needed to be better informed before making a decision on whether or not the ban should be kept or revised.
However, she said, the ban has worked.
"Nobody has been killed by a pit bull since [the ordinance took effect] in Denver," she said.
Still, it hasn't stopped residents from owning the dogs. City officials estimate 4,500 pit bulls are being kept illegally.
Glen Bui, vice president of the American Canine Foundation, plans on going to Denver in the next few weeks with six of the organization's animal behavioral experts. The foundation has filed a lawsuit against Denver claiming that the city violated the constitutional rights of pit bull owners.
Bui said breed-specific legislation doesn't protect the public or stop illegal activity involving dogs and it wastes thousands of dollars of taxpayer money, which could be better spent on enforcement of animal control laws.
Currently 14 states prohibit breed-specific legislation, he said, while several cities, like Pontiac (Michigan), and Algona, (Washington), have recently repelled their bans.
To protect the public from dangerous dogs, Bui believes that legislation should include strong criminal penalties for irresponsible owners who allow their pets to behave aggressively to the point of causing injury.
Instead, he feels that some communities are unjustly singling out certain breeds, like pit bulls, because of false claims that they're genetically dangerous.
"Dogs have been domesticated for thousands of years and within all breeds there can be dangerous dogs because of owner issues, such as training the dog to attack, or lack of training and socialization," said Bui, who is a geneticist. "It is man who is responsible for the dog's behavior, not the breed of dog."
Not everyone agrees.
Tom Skeldon, dog warden of Lucas County in Ohio, said genetics play a big role in how a dog acts.
"Why do golden retrievers retrieve? Why do Border collies herd? Why do pit bulls grab things, hang on, and not let go?" he asked. "That's all a product of genetics. Can it be enhanced with some training? Absolutely. But the genetics have to be there to do that." In 1987 Ohio passed a state law that automatically deems all pit bulls as vicious.
The law does not ban the breed. Instead it requires they be kept properly confined, such as behind a locked fence or inside a house. When in public, pit bulls and their mixes must be kept on a six-foot (two-meter) leash and handled by someone of suitable age, showing proper discretion. Owners must also carry U.S. $100,000 liability insurance.
Skeldon says the law is controversial because it works.
"Ohio's vicious and dangerous dog law is good," he said. "It allows dog wardens, animal control officers, or police officers to not be impotent when it comes to removing obvious public safety threats, in the form of dogs, from neighborhoods."
In 1993 Skeldon said his agency picked up 50 pit bulls. Last year that number rose to 690.
The increase is mainly due to the narcotics trade, he said. When Skeldon goes on police raids, he said they frequently encounter pit bulls used by drug dealers for protection, or dog fighting.
Breeding pit bulls is also profitable. He said puppies sell for U.S. $250 to $500 each and backyard breeders are not removing dogs from their stock that show human aggression.
In addition to the Ohio state law, the city of Toledo has two local government ordinances regarding pit bulls: ownership is limited to only one dogand it must be muzzled when off the owner's property.
The city and state law are currently being challenged as unconstitutional in Toledo Municipal Court. A decision is expected within the next few weeks.
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