The parasite-infested animals were found in a 30 square-metre (323 square feet) house in Izumo, a city in western Japan, last month following complaints from neighbours.
Kunihisa Sagami, the head of the animal rights group Dobutsukikin, said the dogs were found crammed onto shelves and under tables and chairs.
“The entire floor was filled with dogs and all the floor space you could see was covered with faeces,” Sagami told Reuters.
The increase in reports of hoarding has raised concerns about the welfare of both the animals and their owners.
In the year through to the end of March 2019, local authorities received more than 2,000 complaints about homes overrun with animals, according to the environment ministry.
A ministry analysis of 368 cases showed about 30% of the owners were aged 70 or over, with a significant number living with dementia. More than half of the people questioned said they were living in “difficult” circumstances, including poverty, poor health and isolation.
In response, Japan’s animal welfare law has been revised to force owners to neuter or spay their pets where over-breeding is a risk, and penalties for animal abuse have been increased. Animal welfare officials now have the power to conduct an on-the-spot inspection if they suspect an owner of cruelty.
“There is a tendency … to treat issues around animals lightly, but if we don’t approach the owners of these pets with a view to providing welfare, then we can’t solve the problem,” a local government official told the Mainichi Shimbun,
In June, a man in his 50s was arrested after animal rights activists rescued 66 dogs he had been keeping in foul conditions in an unoccupied house. The man did not live with the animals, but visited the house every two or three days to feed them.
Dogs are not the only victims. In March, 238 cats were discovered living in unsanitary conditions in a house in northern Japan before being placed under the protection of local authorities and animal rights groups.
In another case that made headlines last year, animal support volunteers entered the Tokyo home of a woman and her elderly mother to find a tiny room filled with 163 cats.
Public health officials first visited the house in Izumo seven years ago after neighbours complained about the noise and smell, but the occupants – a family of three – refused to allow them in.
They later told officials that that the number of dogs had multiplied because they could not afford to have them spayed or neutered.
Sagami said his group would find foster homes for the dogs after the family agreed to give them up.