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Are There Better Alternatives to Spaying and Neutering Dogs?

Dog reproduction can be controlled without disrupting normal hormonal balance.

Key points

  • In North America, 70 to 80 percent of dogs are spayed or neutered to prevent reproduction and control problematic behaviors.
  • Recent studies show that spayed and neutered dogs are actually more likely to show aggressive and fearful behaviors.
  • Using hormone-sparing spay and neutering procedures results in better health outcomes and fewer problematic and nuisance behaviors.
Chris and Yoon Choi/Flickr CC BY-NC-SA 2.0
Chris and Yoon Choi/Flickr CC BY-NC-SA 2.0

In North America, between 70 and 80 percent of dogs are spayed or neutered. This is done to prevent the overpopulation problem that has forced many shelters to euthanize countless dogs. It is also commonly recommended that male dogs be neutered to prevent aggression or other problematic behaviors.

A number of veterinarians and behaviorists suggest that this procedure should be done as early as possible "before aggressive tendencies become set." Because of the belief that neutered dogs are less likely to be aggressive, many dog parks, apartments, and dog boarding kennels require that pets at their facilities be surgically altered. A Google search reveals that in the United States, 31 states and the District of Columbia require that animal shelters spay or neuter dogs before they can be adopted.

Unfortunately, there is mounting scientific data suggesting that spaying or neutering may be associated with a higher probability of physical problems, and two large sample studies have suggested that these procedures may actually result in increased canine aggression, fearfulness, and overexcitability. A new study confirms these results and suggests alternatives that can prevent reproduction but will not have negative psychological consequences.

What Is Involved in Spaying and Neutering?

It is important for you to understand what is done medically to prevent reproduction in dogs. Spaying (technically ovariohysterectomy) is a surgical procedure in which both the uterus and the ovaries are removed. This obviously will prevent reproduction; however, removing the ovaries also prevents the production of the normal female hormones, which play a role in the chemical balance of the brain and body and perhaps even affect memory.

Neutering of male dogs is usually done by castration, which involves the removal of the testes. This stops reproduction but also causes a loss in the ability to produce male hormones such as testosterone. The imbalance caused by the absence of this hormone can cause significant behavioral and physical changes and may impair some forms of cognition.

Are There Usable Alternatives to Spaying and Neutering?

Is it possible to block reproduction in dogs without disturbing the hormonal balance that might be involved in controlling behavior? Fortunately, there is. For male dogs, one can perform a vasectomy, which involves cutting or tying off the vas deferens (a coiled tube that carries the sperm out of the testes). This surgical procedure leaves the reproductive organs intact while blocking the means of reproduction. Most importantly, it allows the testes to continue to produce testosterone, which should mean that the dog will continue to have the same behavioral characteristics as an unaltered male dog.

For female dogs, there is the possibility of a hysterectomy, or "ovary-sparing spay." In this procedure, a dog's uterus is removed, but the ovaries are left intact. The ovaries are a key part of hormone regulation in females. Since the ovaries are still functioning, although the dog can no longer reproduce, she will still go into heat. More importantly, all of the physiological and behavioral processes controlled by her hormones should remain unchanged.

That is the theory; however, no studies have been conducted to see if these hormone-sparing vasectomies and hysterectomies actually result in a different set of outcomes than the traditional spaying and neutering. Fortunately, a new study from a team led by Christine Zink, formerly of Johns Hopkins University and currently at Integrative Sports Medicine in Ellicott City, Maryland, provides that needed information.

This was a large study involving 6,018 dog owners, mostly from the United States and Canada. Participants answered a rather extensive online survey (36 pages), which gathered information on the health status and demographics of their pets. The participants were also asked about two categories of behavior problems: problematic behavior (including aggression, anxiety, and fearfulness) and nuisance behaviors (urine marking and mounting—normal canine behaviors that many dog owners find objectionable).

It's All About the Hormones

The researchers found that the most important variable in predicting behavioral and health outcomes has to do with how long the dog's body had exposure to the gonadal hormones. Think of it this way: A dog that has been spayed or neutered early in life only has brief exposure to sex hormones. Dogs that have been spayed or neutered later have a longer exposure to these hormones, while dogs that are intact or have had the hormone-sparing vasectomies or hysterectomies have the longest exposure to these hormones. It appears that the body and brain benefit from maximum exposure to the sex hormones.

Generally speaking, the animals that had the traditional spaying and neutering suffered from more health problems than the animals that were left intact. These included orthopedic problems, susceptibility to cancer, endocrine difficulties, increased likelihood of obesity, and shorter life expectancy. Generally speaking, the results show that the dogs that had vasectomies or hysterectomies fared better than those that had the traditional spaying and neutering.

Since our focus is on behavior, the most important outcomes of this new study were that they confirmed the earlier findings that spaying and neutering resulted in a significant increase in problematic behaviors (aggression and fearfulness) compared to intact animals. The spayed and neutered dogs also had a higher incidence of nuisance behaviors. The behavioral changes were much less apparent in dogs with vasectomies and hysterectomies apparently because they still had functioning gonads (testes and ovaries) and, thus, benefited from the longer exposure to normal amounts of sex hormones.

Should Dogs Be Spayed or Neutered?

The researchers summarize their results saying that their most important finding was that the longer the duration that gonads were present (regardless of current reproductive status), the less likely it is that there will be general health problems and problematic or nuisance behaviors.

Because vasectomies and hysterectomies permit dogs to experience longer gonadal hormone exposure times, the researchers conclude that "when electing surgery to prevent reproduction, dogs might benefit from these alternative surgeries, with respect to general health and experience better behavior outcomes, compared to undergoing traditional spay-neuter surgery."

They also note that "Delaying traditional spay-neuter surgery could offer similar benefits," which flies in the face of the recommendations often made by some veterinarians who suggest that earlier spaying and neutering is the preferred course of action.

Copyright SC Psychological Enterprises Ltd. May not be reprinted or reposted without permission.


Zink C, Delgado MM, Stella JL. (2023). Vasectomy and ovary-sparing spay in dogs: comparison of health and behavior outcomes with gonadectomized and sexually intact dogs. J Am Vet Med Assoc. 2023 Jan 19:1-9. doi: 10.2460/javma.22.08.0382. Epub ahead of print. PMID: 36656681.

McGreevy PD, Wilson B, Starling MJ, Serpell JA (2018) Behavioural risks in male dogs with minimal lifetime exposure to gonadal hormones may complicate population-control benefits of desexing. PLoS ONE 13(5): e0196284.

Coren, S. (2018, 9 May). Neutering Causes Behavior Problems in Male Dogs. Psychology Today, Canine Corner.

Coren, S. (2017, 22 February). Are There Behavior Changes When Dogs Are Spayed or Neutered? Psychology Today, Canine Corner,

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