A TWO-YEAR undercover investigation by animal activists reveals shocking footage on the widespread practice of killing pigs by carbon dioxide.

Three Victorian abattoirs are at the centre of animal abuse allegations highlighted in the video that activists claim shows what really happens when pigs are lowered into “gas chambers”.

Animal activists have this morning chained themselves to the Diamond Valley Pork abattoir in Laverton and say they plan to block trucks transporting pigs.

Police have been negotiating with protesters who have been on the roof and chained to a pig run inside the property since about 2am.

The abattoir says on its website that it is export and RSPCA accredited, and activists agree the business’ processes are considered “best practice”.

Most pigs in Australia are killed by carbon dioxide. But Animal Liberation Victoria says the public is being fooled into thinking that pigs “gently fall asleep”.

“Most pigs in Australia, including those raised ‘free range’, are killed in these carbon dioxide gas chambers, which are regarded as ‘best practice’,” ALV said.

“The industry tells the public that gas chambers are a humane slaughter method and wants us to believe that the pigs gently fall asleep, however nothing could be further from the truth.”

An activist claims in the video that the pigs “struggle violently”.

“It’s like being choked under water until you fall unconscious,” he says.

“In their last minutes, these pigs are burning from their inside out.”

The three businesses named in the video are Diamond Valley Pork and Australian Food Group, both in Laverton, and CA Sinclair in Benalla. The Herald Sun has contacted all of the abattoirs for comment.

ALV said the video was the result of the undercover investigation which involved climbing into a “gas chamber” while wearing an oxygen tank to position hidden cameras.

The footage shows pigs poked with what is allegedly a mains-powered electrical prodder before being put into metal cages and gassed.

ALV founder Patty Mark said the protesters would stay until they were forcibly removed.

“We’re going to try to stay here as long as we can, because so far we’ve managed to shut down the slaughterhouse — the workers are out the front with nothing to do,” Ms Mark said.

“We’re arguing that slaughterhouses be shut down — they’re very violent, the animals are being traumatised.

“We know it’s a major change for people to think about but it’s important.”