Photos are from a Google search on "animal hoarding"
From the American Veterinary Medical Association
Animal Hoarding - Accumulats a large number of animals, overwhelming the person's ability to provide even minimal standards of nutrition, sanitation, and veterinary care. Fails to acknowledge the deteriorating condition of the animals (including disease, starvation, and even death) and household environment (severe overcrowding, very unsanitary conditions). Fails to recognize the negative effect of the collection on his or her own health and well-being, and on that of other household members.
Animal hoarding may be symptomatic of psychologic disorders such as dementia, addiction, attachment disorder, or obsessive-compulsive disorder.
Additionally, animal hoarding can create severe hazards to the health of the hoarder, family members, and the animals involved.
Household conditions often deteriorate to the point where appliances and utilities are not functioning, and proper food preparation and basic sanitation measures become impossible, according to an article in Municipal Lawyer magazine by the consortium. There may also be rodent or insect infestations, fire hazards, or dangerously high concentrations of ammonia in the house.
Animal Hoarding is a mental illness recognized as a psychological condition; a variant of obsessive-compulsive disorder. The distinguishing feature is that a hoarder "fails to provide the animals with adequate food, water, sanitation, and veterinary care, and … is in denial about this inability to provide adequate care." At the very least, because hoarders, by definition, fail to clean up after the animals. The sometimes hundreds of dogs or cats kept by a single hoarder generally show signs of neglect such as severe malnutrition, untreated medical conditions including open sores, cancers, and advanced dental and eye diseases, and severe psychological distress. In 80 percent of the cases studied, authorities found either dead or severely ill animals in hoarders' homes. -Wikipedia
"Hoarding is very often a symptom of a greater mental illness, such as obsessive-compulsive disorder. For most hoarders, it is likely that their actions are the result of a true pathology, even though they are still usually able to function quite well in society," says Randall Lockwood, HSUS vice president for Research and Educational Outreach.
Because animal hoarders quite often appear to lead normal lives, it's important to recognize when a person's fixation with animals has gotten out of control. The HSUS defines an animal hoarder as a person who has more animals than he or she can properly care for. Another defining characteristic is the hoarder's denial of his inability to care for the animals and his failure to grasp the impact his neglect has on the animals, the household, and the human occupants of the dwelling.
What's more, hoarders are usually well-educated and possess excellent communication skills. Many hoarders have an uncanny ability to attract sympathy for themselves, no matter how abused their animals may be, which is often how hoarders manage to fool others into thinking the situation is under control.
Anyone who is considering relinquishing an animal to a private rescue group should first visit the premises and ask to see where the animals are kept. -The Humane Society of the United States
Every hoarder’s behavior translates into severe, even fatal, neglect for animals in their custody. Overcrowded and filthy conditions make for easy transmission of worms, fleas, mange, ear mites, upper respiratory infections, parvo, distemper, and other diseases and can lead to feces-matted coats and urine burns. Hoarded animals are commonly deprived of basic veterinary care, including spaying and neutering, which causes the numbers of animals to increase, and/or results in the separation of animals by sex and their confinement to small cages or bathrooms. Injuries—including broken limbs and wounds suffered in fights with other animals—go untreated and lead to infections. -PETA
What is the difference between an animal hoarder and a puppy mill? A puppy mill cranks out puppies for a profit. They keep their expenses low in order to increase the profit margin. Therefore low grade food, not vetting, overcrowding are all examples of puppy miller's attempts to keep their expenses down and increase their profits. It's all for money. It is a business to them. Animal hoarders often think they are saving the lives of the animals and have no intention of making a profit. They don't sell their animals. They just keep collecting them. Income vs. Expense is not a part of their dialogue.