By Carmen Cheek

overpopulation at shelter
Vulp / AdobeStock
Over six million dogs and cats enter US animal shelters every year, and far too many of those shelters are overcrowded. Especially in southern states, animal shelters are forced to house multiple pets in the same cage or turn homeless pets away. Many shelters must resort to euthanization; each year, 920,000 shelter animals are euthanized.

What is fueling pet overpopulation and high euthanasia rates? Learn about the impacts of pet overpopulation and how you can help.

The causes of pet overpopulation

The driving force of pet overpopulation is irresponsible people and their common, yet harmful, practices, including:

  • Not spaying or neutering pets:

In many communities, it is common for pet parents not to neuter or spay their dogs and cats, and these same people allow their pets to roam freely or dump them. According to the North Shore Animal League, just one unspayed female dog (and her litter) can produce up to 67,000 puppies in just six years. Because pets can produce an abundance of offspring quickly, overpopulation can happen rapidly if not managed, which is sadly the case in many areas in the country. By making the simple choice of spaying and neutering our pets, we can help combat pet overpopulation.

  • Lack of education:

Some communities may not know about the advantages of shelter programs such as foster care, behavioral therapy, affordable spaying and neutering services, post-adoption training and help, trap-neuter-return, and the important role of volunteers. By implementing these overpopulation solutions, shelters can increase adoption rates, reduce intake, and decrease euthanasia rates.

The rise of the puppy mill

The U.S. Department of Agriculture encouraged farmers devastated by the Great Depression to breed animals, including puppies, as a new “cash crop” for the growing pet store market. That, combined with a general view of animals as disposable, overcrowded shelters by 1970, led to massive pet overpopulation and huge euthanasia rates.

The good news is that overpopulation and euthanasia numbers have decreased significantly in recent years. While still huge, we’ve certainly made a lot of progress since 1970. Thanks to a changing view of pets as part of the family. This has also spurred spay/neuter efforts, increased rescue and advocacy organizations, and increased legal action for animal cruelty.

The consequences of pet overpopulation

The primary consequence of pet overpopulation is, of course, the poor quality of life and outcomes for the excessive number of homeless pets themselves. That said, pet overpopulation also negatively affects humans in a couple of ways.


American taxpayers pay an estimated $2 billion annually for animal control, animal shelter maintenance, and euthanasia/disposal. This large sum of money could be used elsewhere for other important matters, such as affordable spay and neuter procedures or behavioral services. Instead, we use it to regulate this human-generated problem.


Stray pets are sometimes called “disease reservoirs” due to their likelihood of introducing diseases to surrounding wildlife. Rabies, toxoplasmosis, and canine distemper virus (CDV) are some of the most common diseases transmittable from pets. Disease transmission not only presents health hazards for native wildlife and surrounding animal populations, but also for humans. This is why it is important for us to provide our pets with necessary vaccines and to regulate where they roam.

Threat to wildlife

We often forget that man’s best friends are not native to most environments. Dogs are skilled hunters, and even small packs have the potential to prey on large numbers of local wildlife. This was proven in New Zealand, where one dog killed approximately 55% of the kiwi population within a six-week period. Dogs and cats introduced to a new environment only add to natural predation levels and result in some species of prey not being able to survive. These potential impacts can eliminate native populations and damage intact ecosystems if the problem is not addressed.

Pet overpopulation prevention

The high occupancy of animal shelters around the world shows that there is a lack of knowledge in proper pet care, community services, and understanding of the impacts of overpopulation. Pet sterilization, public awareness about pet overpopulation, and better education for pet parents are all needed to help solve this issue. But what can we do to help address pet overpopulation and the burdens it brings?


Donating to organizations combating pet homelessness is helpful since it augments these groups’ impact. Local shelters and rescues, humane societies, and spay/neuter organizations are great places to donate. In addition to funding housing pets, donations also go toward educational services to keep pets in their homes, such as pre-and post-adoption training, foster programs, and behavioral therapy.


Adopting a pet from a shelter or rescue is a great way to offer a caring forever home to animals who may otherwise be left in overcrowded shelters or wandering the streets. When more pets are adopted, it reduces the pet overpopulation problem in animal shelters. This results in more resources and space for other animals in need, which in turn helps prevent overpopulation and reduce the burden on shelters. Adoption also decreases demand for mass breeding facilities such as backyard breeders and puppy mills.


Pet parents must learn how to responsibly care for their animals to help combat pet overpopulation. There are many considerations to think about before adopting a pet — from lifestyle, financial ability, and living situations. To be responsible, we can spay or neuter our pets. Pet parents also need to commit to care for their pets for their lifetime and provide them with quality care.

Pet overpopulation statistics

How many pets are euthanized each year?

Shelters around the United States euthanize an estimated 920,000 shelter animals each year.

How many dogs are euthanized in shelters each year?

An estimated 390,000 dogs are euthanized in shelters around the United States each year.

How many dogs are in the US?

There are over 76 million dogs estimated to be in the United States.

Do kill shelters still exist?

Unfortunately, kill shelters, or shelters that perform euthanasia for reasons beyond irreparable medical or dangerous behavioral issues, still exist.

How many no-kill shelters are in the US?

According to Best Friends Animal Society, approximately 57% of county shelters in the US are no-kill.

What states are no-kill states?

Delaware is the only fully no-kill state, while Vermont, Rhode Island, North Dakota, and New Hampshire have the smallest number of pets being euthanized. Texas, California, North Carolina, Florida, and Louisiana (and a number of other states) euthanize the most pets.

How long do animals stay in shelters before euthanized?

The length of time animals stay in shelters before being euthanized varies but can range from a few days to several weeks or months, depending on the shelter’s policies and the individual animal’s circumstances.

How long does the SPCA keep animals?

Each SPCA has its own policies regarding the length of time they keep shelter animals.

How many puppies come from puppy mills?

Puppy mills produce approximately 1.2 million puppies a year. The Humane Society estimates there are over 10,000 puppy mills in the US.

Are breeders regulated?

Breeders are subject to regulation, however, the Animal Welfare Act, which is the only federal law governing puppy mills, only requires that an animal be kept in a cage six inches longer than its body in any direction.


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Carmen Cheek is a graduate student at Miami University studying the impacts of dog overpopulation, a long-time pet sitter, and a kennel technician.