Anyone considering buying a puppy for their family this holiday season may be unwittingly supporting cruel breeding conditions, vets and the RSPCA warn.

While states like Victoria are trying to stamp out the puppy farm trade, RSPCA investigators have seen dozens of dogs across the state bred in conditions unfit for household pets.

RSPCA Victoria head of prevention Sophie Buchanan said she and her colleagues had witnessed some appalling breeding environments.

"We've seen dead animals among live animals, we've seen female dogs bred until they physically are starting to collapse," Ms Buchanan said.

"We've seen puppies living in amongst excrement with food scattered across the floor, water bowls that are not just empty but clearly have been empty for significant periods of time."

Ms Buchanan said illegal puppy farms are big business, and Victoria provides the perfect environment for them to flourish.

The RSPCA estimates between 60,000 and 70,000 puppies — or about 75 per cent of the new puppy market — are sold in Victoria with unclear origins every year.

"One of the reasons why a number of breeders base themselves down here is because we have a pretty temperate climate," she said.

"[It] is also free from a lot of the issues that we have in more northern parts of Australia like ticks and parasites and health issues and terrible diseases that can happen in other parts of Australia."

RSPCA investigators have seen dozens of dogs across Victoria bred in conditions unfit for household pets. ( Supplied: RSPCA )

Animals housed in poor conditions can also have trouble socialising with other dogs and suffer growth problems, according to Paula Parker, president of the Australian Veterinary Association.

"These puppies and kittens are much more likely to come into contact with viral disease, with bacteria and with parasites," Dr Parker said.

"And so if people do come into possession of one of these animals, the best thing to do is to go in and see their local vet."

New pet owners urged to do research

Puppy farms are a major animal welfare issue, with problems including extreme confinement. ( ABC News: Eliza Laschon )

The Victorian Government has passed new legislation to try to stop puppy farms, including the creation of a statewide pet exchange register.

The new rules will also ban pet stores from selling puppies and kittens, but Dr Parker is concerned this could just lead to more puppies being sold elsewhere.

What is a puppy farm? An intensive dog-breeding facility operated under conditions that fail to meet dogs' behavioural, social or physiological needs

An intensive dog-breeding facility operated under conditions that fail to meet dogs' behavioural, social or physiological needs Usually large-scale commercial operations, but inadequate conditions may also exist in small-volume breeding establishments

Usually large-scale commercial operations, but inadequate conditions may also exist in small-volume breeding establishments Puppy farms are a major animal welfare issue, with problems including extreme confinement, inadequate care and overcrowding

"If we cut off the public-facing part of that supply chain in the pet store, have we dealt with the supply chain that's behind them or are we encouraging those people to sell [online]?," Dr Parker said.

"[However] all of the shelters put in a lot of work to make sure that these dogs have had their health status assessed and they go through a behavioural assessment.

"So it's something to think about adopting one of those pets and giving them a second chance at life."

The Victorian Government has passed new legislation to try to stop puppy farms. ( ABC News: Kellie Scott )

But even after the laws take effect next year, Ms Buchanan said those wanting a pet should find out as much as they can about their new dog's parents.

"Make every effort to make sure you see the home or facility in which that animal was bred so you can reassure yourself that the welfare conditions have been good for that animal," Ms Buchanan said.

"[If you cannot do that], we would say don't buy it. Make sure that you look for the next animal where you can do that."