The parliamentarians who wrote the Canada's bestiality law understood the word to imply the physical penetration of an animal, and it is not the role of jurists to broaden the definition to include other acts, the country's top court ruled Thursday.

In a decision that was supported by all but one of seven justices, the Supreme Court upheld the acquittal of a British Columbia man who was charged with bestiality after compelling the family dog to sexually abuse his 16-year-old stepdaughter.

Lawyers for the man, who was also convicted on 13 counts of sexually molesting his two stepdaughters over a 10-year period, argued that the 1954 law prohibiting bestiality had a specific meaning: vaginal or anal penetration of an animal. The Supreme Court justices agreed, saying it would be inappropriate for courts to expand that definition beyond what was intended by the politicians who drafted the legislation.

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"Penetration has always been understood to be an essential element of bestiality," Justice Thomas Cromwell wrote on behalf of the majority. "Parliament adopted that term without adding a definition of it, and the legislative history and evolution of the relevant provisions show no intent to depart from the well-understood legal meaning of the term."

Courts should not broaden the scope of liability for the crime through common law, Judge Cromwell wrote. "Any expansion of criminal liability for this offence is within Parliament's exclusive domain."

The man from Prince George, who cannot be identified, was sentenced to 16 years for all the offences upon which he was convicted, including two related to the bestiality count. The judge in that case decided that bestiality in the Criminal Code meant touching between a person and an animal for sexual purposes, and penetration was not required.

In the British Columbia case, the man used peanut butter to compel the dog to perform a sexual act with his stepdaughter while he used a videocamera to record the incident.

But the man's bestiality conviction was overturned by the B.C. Court of Appeal which concluded that penetration was an essential element of bestiality. So lawyers for the province took the case to the Supreme Court.

An animal rights group called Animal Justice appeared before the Supreme Court as an intervenor in the case when it was heard last fall. Lawyers for the group said modern societal morals include protecting vulnerable beings from sexual conduct to which they cannot consent.

Supreme Court Justice Rosalie Abella agreed with that argument.

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"I do not see the absence of a requirement of penetration as broadening the scope of bestiality," she wrote in her dissenting opinion. "I see it more as a reflection of Parliament's common sense assumption that, since penetration is physically impossible with most animals and for half the population, requiring it as an element of the offence eliminates from censure most physically exploitative conduct with animals."

But the majority were unconvinced.

"When Parliament uses a term with a legal meaning, it generally intends the term to be given that meaning," they said in their decision. "In this case, the term bestiality did have a clear legal meaning when Parliament used that term without further definition in the English version of the 1955 Criminal Code. Bestiality meant buggery with an animal and required penetration."

Camille Labchuk, a lawyer who is also the executive director of Animal Justice, said the Supreme Court decision is "a wakeup call" that criminal laws protecting animals in Canada are severely out of date.

"As of today, Canadian law gives animal abusers a licence to use animals for their own sexual gratification," said Ms. Labchuk. "The Supreme Court has essentially thrown the ball into Parliament's court and we're calling on Parliament to step in immediately to fix our outdated laws and protect vulnerable animals from sexual exploitation."

Ms. Labchuk urged the government to support a private member's bill introduced in Parliament earlier this year by Liberal MP Nathaniel Erskine-Smith which outlaws a number of acts related to the killing or harming of animals and broadens the definition of bestiality. Although the bill essentially mirrors legislation that was introduced twice by previous Liberal governments but did not get passed into law, Ms. Labchuk said the current Liberal government is not supporting it.

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The government has been swayed by hunting groups and fishing groups that the bill would shut down all industries that rely animal use, said Ms. Labchuck, who dismissed that notion as "preposterous."

Justice Minister Jody Wilson-Raybould said her concern is that Mr. Erskine-Smith's bill proposes significant amendments to the criminal code. "This is an important issue that deserves careful study," Ms. Wilson-Raybould said. "Any amendments to these provisions should be informed by broad consultations with Canadians."