ABC Online - Radio Australia reports that 7.30 has obtained footage of hens being boiled alive at the Star Poultry Supply slaughterhouse in the suburb of Keysborough.

The video was secretly recorded earlier this year by animal rights campaigner Tamara Kenneally and a group of friends.

"I do want people who eat eggs to watch it just to know what's happening to those girls," she told 7.30.

"Cage girls, barn girls, free range girls — they all die like this."

'Something has gone horribly wrong'

The abattoir slaughters egg-laying hens that are considered "spent" when they are 18 months old.

Industry regulations require chickens to be stunned and then immediately killed by a slit to the throat.

They are then plunged into a scalding bath designed to strip off their feathers.

However, the footage shows many chickens still conscious when they are dipped into the boiling water.

"The footage is extremely horrific and very distressing to watch," the RSPCA's chicken welfare specialist Kate Hartcher said.

"Animals in all abattoirs need to be stunned prior to slaughter so that they're unconscious while they're being slaughtered.

"In this case something has gone horribly wrong."

No formal investigation by Agriculture Victoria

Animal activists who planted the cameras inside the facility gave the footage to Victoria's abattoir regulator, PrimeSafe, in March this year.

PrimeSafe investigated and referred the footage to Agriculture Victoria, which is responsible for enforcing the state's animal cruelty laws.

"That complaint was investigated and substantiated by PrimeSafe due to breaches of Australian Standards," PrimeSafe said in a statement.

"The business was subject to enforcement action and increased regulatory oversight until improvements in animal handling, including back-up slaughter, were implemented."

Agriculture Victoria said authorised officers spoke to the company's management, but did not initiate a formal animal cruelty investigation.

"Agriculture Victoria was satisfied that the remedial action being taken by the company, at the direction of PrimeSafe, and some staff changes would help manage the instances of poor practices demonstrated on the footage," the department said in a statement.

'Abattoir shouldn't have been running at all'

The RSPCA's Dr Hartcher has questioned why Star Poultry was allowed to continue slaughtering chickens while it was under investigation.

"We think that the abattoir should have been immediately shut down until all animal welfare risks can be avoided and any problems can be rectified," she said.

"It was extremely poor practice and it was a systemic problem in the abattoir.

"The abattoir shouldn't have been running at all."

Victorian abattoirs are subjected to four audits to check their compliance with animal welfare and food safety standards.

The audits are carried out by independent contractors on behalf of PrimeSafe.

PrimeSafe says Star Poultry was subjected to four audits in the 12 months leading up to its investigation.

Star Poultry did not respond to 7.30's request for an interview.

You can view the video footage of the events at Star Poultry Supply's abattoir by clicking here.