An investigation into forging veterinary documents led police to a puppy mill with dozens of dogs in a pitiful state.

Police went to a home in Saint-Gabriel-de-Brandon on Wednesday, about halfway between Montreal and Trois Rivieres, to arrest a woman suspected of fraud and forgery when they discovered the house was occupied by dozens of small dogs.

Officers said the stench was so terrible they had to call in the fire department to ensure the air quality of the house was safe enough for them to enter.

“There was an overwhelming smell of dog urine and feces,” said Saint-Gabriel-de-Brandon fire chief Frederic Cyr. “It really pierced through everything.”

They also called the Ministry of Agriculture, Fish, and Food for assistance, as well as the SPCA Montreal, and those agencies seized 70 dogs, including Yorkshires, Malteses, and Chihuahuas.

Some of the animals were kept in cages while others roamed free throughout the house.

They also found four dog carcasses. At least two dogs were covered in paint – in both cases, the head and tail were one colour and the body a different colour.

“We discovered dogs that were painted. We don't know why. The head and tail were blue and the body yellow,” said Cyr.

Many seemed as if they had not been fed in days, if not weeks.

A number of old newspapers were found on the floor to help with the dogs’ droppings. Police said the house was filthy.

The arrest was prompted after many people who had purchased dogs complained to the Order of Veterinarians.

The dogs, being sold on Kijiji or Lespacs for up to $1,200, were coming with veterinary certificates indicating the animals had a clean bill of health and had been vaccinated. In reality the dogs the woman was selling were in poor shape, with one dog dying just days after being sold.

The complaints prompted an investigation, and Wednesday's arrest.

Police said a 44-year-old woman could be charged with fraud and forging documents. They will also recommend charges of animal cruelty. She has been released by police.

“I've never seen one here and in 25 years of service,” said Cyr. “It's the first time I've seen a puppy mill like this one.”

Quebec has a reputation as the puppy mill capital of North America.

In 2015, the province unanimously passed a law defining animals as sentient beings, making tougher punishments for animal cruelty.

Fines can now range from $250 to $250,000, and serial violators could face up to 18 months in jail.

The animals in this case have all been placed in the care of the Montreal SPCA, but are not available for adoption for now.

The house has been declared unfit to live in.