Plastic and other pieces of rubbish are being processed with meat to make a key pet food ingredient because of shoddy industry practices, a former insider has revealed.

Dennis Pedretti told 7.30 that in his previous job as a rendering plant operations manager, it was too difficult to remove animal ear tags and other objects from carcasses and offal that came from abattoirs and butchers.

His revelations coincide with a push for a Senate inquiry to examine the $4 billion self-regulated pet food industry.

"Well, you have sheep heads come through, they have an ear tag. They go into the pit," Mr Pedretti told 7.30.

"There would be plastic. Butchers would be getting rid of their material and they don't care what they're putting in the bin — plastic, cans, all those sorts of things you would see."

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'Who gives a stuff about your dog?'

The type of livestock tag that often ends up in pet food ( Source: WA Department of Primary Industries )

At rendering plants, a cooking and drying process is used to turn carcasses and offal into what's known as protein meal, a dry product used to make stock and pet food.

"It's ground up and crushed up and then goes through the cooking process, so the ear tags, with the heat, effectively melt," Mr Perdetti said.

"It's probably the dollar that takes over. It's more necessary to push it out and make more money. Who gives a stuff about your dog at the end of the day?"

Mr Pedretti's former employer was Australian Tallow Producers in Melbourne. He worked there from late 2010 to 2012.

Another worker who left the plant last year has corroborated Mr Pedretti's account.

Mr Pedretti doesn't know which pet food companies were customers.

"The quantity going out was in containers, 20-tonne containers, and a lot of containers went out every day," he said.

"That's a lot of product and a lot of containers, a lot of customers."

Live, plucked chickens sent for rendering

Chickens being prepared for plucking. ( Supplied by The Australian Chicken Meat Federation )

Mr Pedretti said one day two live chickens arrived at the factory among a truckload of offal.

"They'd been through the whole process of being de-plucked, they'd missed the decapitation," he said.

"They must have ducked at the right time."

He took the chickens home and kept them as pets.

Australian Tallow Producers is well known among locals in the Melbourne suburb of Brooklyn for the foul smell of its operations.

It has been ordered by the courts to pay more than $200,000 for air pollution offences.

The company declined to respond to Mr Pedretti's allegations, instead preferring industry body the Australian Renderers Association to speak on its behalf.

The Association's executive officer Dennis King conceded contamination was an industry-wide issue, and said it was working to educate abattoir workers to remove objects, including animal ear tags.

Pieces of coloured plastic in dog food ( Source: Facebook )

"It's not done on purpose," he told 7.30.

"I think it's more a case of people just don't know because quite often it's a low-paid, low-skill job in that area.

"To a lot of people they think it's just another area that's going away that's waste.

"They don't even know it's pet food quite often."

Mr King said butchers and supermarkets were responsible for throwing plastic gloves in with meat bound for pet food.

"It's a case they've got a bin here, a bin here, a bin here and the brain might go into neutral, it's time to rush off to lunch or something, and they just happen to throw it into the wrong bin," he said.

"I'm a pet owner myself, I'd be upset, too, when I saw there was contamination or a bit of plastic."

He believed the plastic was unaffected by the cooking process.

"Obviously it's being identified when it's in the pet food so it's still there, it's been broken up into small pieces so it's identifiable," Mr King said.

"I believe the industry as a whole has improved dramatically over the last few years."

Contamination problems known in industry

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Plastic and other contamination is an open industry secret and has been laid bare in the Renderers Association newsletter, Rendering Circles.

In one issue obtained by 7.30, pet food company Nestle Purina, which makes Supercoat and Lucky Dog, is quoted as receiving 295 customer complaints about foreign objects in 2015, mainly metal and plastics.

The association goes on to state that "foreign body contamination means loss of money to a pet food company".

Nestle Purina said it couldn't "reconcile" the figure of 295 with its records and wouldn't reveal how many customer complaints it has had since, except to say that its figures were much lower.

The pet food company said it inspected all deliveries for foreign object contamination and had magnets, sieves and metal detectors to find and remove unwanted material.

Mr King said the rendering industry was also looking at new technologies to reduce contamination.

"We process in Australia about 30 million head of cattle and sheep every year.

"All of those have to be identified by law, so it's mainly done by (animal ear) tags. And so … 30-odd million tags are going through the abattoir system every year.

"We're working to try to take tags and have them magnetised, and then it's much easier to get the plastic picked up if we can use magnets."

Pet food standards should be 'same other foods'

A piece of metal found in dog food ( Source: Facebook )

Veterinarian Andrew Spanner believes the only way companies throughout the pet food supply chain will lift their game is if the industry is regulated.

"The industry can only be trusted when it is subjected to the same standards that other foods are subjected to," he said.

"If you do the wrong thing in the pet food industry at the moment it's unlikely anybody will know about it, and it would tend to create a condition of slackness, especially towards food safety."

7.30 has spoken to a number of owners who've found plastic and other objects in pet food.

Just last month an owner discovered a shard of metal in dog food sold at supermarket chain Aldi.

In a statement, Aldi said its supplier had metal detection equipment and the incident was an isolated one.

South Australian Senator Stirling Griff said he was disturbed by the industry's failings and planned to take action this week in Canberra.

"I'm very concerned and any pet owner, and in fact any decent human being, would also be very concerned and the majority of us would be very surprised to know this industry is totally unregulated," he told 7.30.

"What we're proposing is to put forward to my Senate colleagues an inquiry on the pet food industry, with a particular focus on the recall systems in Australia."

The pet food industry was thrown into the spotlight in March, after more than 100 dogs were struck down with the debilitating condition megaesophagus, believed linked to popular dry dog food Advance Dermocare.

It was pulled from shelves three months after the manufacturer Mars Petcare first learned of a potential problem with its product.

Other pet food complaints include mould in Applaws dry dog food, and claims of nausea, vomiting and even seizures from pets eating Baxter's brand sold at Woolworths.

The Agriculture Minister David Littleproud was unavailable for interview but was seeking state and industry support for a review into pet food manufacturing.