Graphic: Tasmanian abattoir investigated over animal cruelty Storyful

Shocking undercover video footage taken at an Australian abattoir in Tasmania has led to allegations of severe cruelty and an investigation by animal welfare authorities. Film from the slaughterhouse, in the Derwent valley, north of Hobart, was taken by concealed cameras at the Gretna Quality Meats headquarters over four days last month.

Animal welfare groups say that the video shows prolonged and unlawful suffering of pigs, sheep and cows.

After the footage emerged Tasmania's Department of Primary Industries said they were investigating the firm for breaches of the Animal Welfare Act. But the owner of the abattoir, Michael Munning, strongly denied the claims of animal cruelty and invited cameras to look around his facility.

But Emma Hurst, a spokeswoman for the Animal Liberation charity, accused the abattoir of crossing a line."This is grotesque cruelty that we're seeing here...and it's completely unacceptable," she said told Australian broadcaster ABC News. "The footage shows animals being beaten with pipes, kicked in the head ...there's clearly failed attempts to stun the animals."

Munning, said he trusted his workers, despite the shocking images of a rifle being used to kill animals, and other images of several attempts being made to kill larger animals. He added that the small operation employed just three people and the footage was illegally obtained.

"It's very frustrating that somebody's actually gone to the trouble of breaking into the property and actually putting up cameras," he said to the news organisation. "It's a small country abattoir, small country town, it's just something that doesn't happen."

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A pig is pictured being shot with a rifle whilst at the facility in Tasmania Animal Liberation / ABC News

Former meatworks supervisor and vet of 43 years, Dr Andrew Nicholson, nonetheless told ABC News that he had some concerns based on the video. "I'm not a firearms expert but obviously the rifle, as it was used that vision, was not suitable because from what I saw there were at least two shots taken...neither were effective," he said.

It was also alleged that the larger animals, which should have been knocked out, were alive and conscious for a prolonged period of time. Munnings insisted that the animals were already dead. "A lot of the footage shows the nerve reaction from the animal and sometimes it can last up to two minutes, the nerves," he said. "But the animals are already dead."

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A man strikes an animal with a metal pole at Gretna Quality Meats in the Derwent valley, north of Hobart. Animal Liberation / ABC News

The RSPCA called for the immediate closure of the abattoir accused of severe animal cruelty. They cited seven key issues they spotted in the video including: a lack of adequate restraint during stunning, causing unnecessary suffering; multiple instances of ineffective stunning of cattle, pigs and sheep, causing unnecessary suffering; repeated stunning using the same captive bolt device, causing unnecessary suffering; inappropriate use of a captive bolt device on a large pig, causing unnecessary suffering; prolonged restraint of cattle prior to ineffective stunning; poorly designed ramp and pens; and abusive behaviour from a worker.

Gretna Quality Meats said they would be reporting the break-ins to the police.