TORONTO - The bulk of the Ontario government's controversial ban on pit bulls has survived a constitutional challenge.

But two key elements were struck down in a ruling issued today by Superior Court Justice Thea Herman.

Herman declared the definition of a pit bull terrier unconstitutional, and also struck down a provision that allows the province to use certificates from veterinarians to prove a dog is in fact a pit bull.

Attorney General Michael Bryant says the province got "99 per cent" of what it wanted out of today's decision.

Lawyer Clayton Ruby, who led the challenge, said in a brief statement his side has claimed a "substantial" victory, but vowed to file an appeal.

Ruby argued the ban is unconstitutional and too broad because it bans all pit bulls, even though animal experts say the majority of the dogs are friendly family pets.

"People should continue to leash and muzzle their pit bulls; pit bulls are banned are in Ontario, and that has been upheld by the Ontario Superior Court," Bryant said in an interview.

"Pit bulls remain banned, the purebred definitions of pit bulls are banned, anything substantially similar to those purebreds are banned."

The law forces pit bull owners to muzzle, leash and sterilize their dogs or face a $10,000 fine or up to six months in jail - or both. Dogs can't be bred or brought into the province.

Ruby argued statistics suggest there are other dogs more dangerous than pit bulls.

He cited a Canadian study that found that since 1983, 23 fatalities from dog attacks in which 55 dogs were involved. Only one dog involved was a pit bull breed, an American Staffordshire terrier.

In court documents, Crown lawyers argued the ban is necessary to protect the public from potential pit bull attacks.

They said attacks by pit bulls are more deadly than from other dogs and pit bulls often attack viciously without being provoked.