Spanish police have arrested five people accused of operating an unlicensed breeding kennel, while rescuing more than 250 small dogs, mostly Chihuahuas, from appalling conditions in the dark cellar of a house outside Madrid.

Police officers noted that some of the Chihuahuas had a muted bark, and found that the animals had had their vocal cords cut, presumably to prevent them from attracting attention to the secret breeding den under a house in the town of Arganda del Rey.

The five people arrested - including two vets - are said to have earned more than €2 million over a decade of breeding Chihuahuas and Pomeranians.

“The dogs were found in terrible living conditions in terms of health and hygiene, and indiscriminate breeding without any kind of veterinary control had caused the females to suffer a variety of health conditions,” Spain’s National Police said in a statement.

Two puppies were found dead, their bodies frozen and wrapped in newspaper.