Over 80% of dogs in the U.S. have had a spay or neuter, which removes the sex organs (called gonadectomy) and associated hormones. About 15 years ago, veterinarians and researchers started to realize that spayed or neutered dogs were more likely to have certain health problems, such as cancer and joint disorders. The amount of research has increased over the years and indicates that a loss of natural hormones can have significant lifelong health implications. For a thorough review of the data on gonadectomy and canine health, see our Hormone-Sparing Sterilization page.

These health problems likely occur because the natural hormone feedback mechanisms become unregulated in neutered dogs. Research from Dr. Michelle Kutzler of Oregon State University, a veterinary theriogenologist and pioneer in understanding the mechanisms of hormone loss in dogs, indicates that luteinizing hormone (LH) may be the problem. In dogs without natural hormone levels, there is no feedback mechanism to control LH. LH affects many organs throughout the body, and the high levels of unopposed LH likely influence the development of diverse health disorders. These findings underscore the importance of a balanced hormonal system for maintaining optimal health.

Gonadectomy has several positive health outcomes and helps reduce pet overpopulation. Gonadectomized dogs are not as likely to have diseases associated with sex organs, such as mammary, ovarian, and testicular cancers, pyometra uterine infection, and prostate enlargement. Not all dogs will develop health problems after being spayed or neutered. A complex set of variables appears to influence the importance of sex hormones, including the age of the dog when spayed or neutered, the breed, the sex of the dog, and its size. Health issues are common in dogs that undergo spaying or neutering at a young age, as well as in large breed dogs that undergo this procedure before they have finished growing.

To avoid potential health and behavior issues related to spay and neuter, pet owners can choose a hormone-sparing sterilization method, such as vasectomy for males and hysterectomy (also called ovary-sparing spay) for females. For more information, see details on our Hormone-Sparing Sterilization page.

Most dogs have already received a traditional spay or neuter surgery, removing the ovaries or testes. In fact, pet shelters or rescue organizations usually require that dogs and cats are spayed or neutered before adoption. Some of these pets will develop health or behavior issues due to the loss of natural hormones, or spay-neuter syndrome.

In humans, a loss of hormones due to injury or disease would be treated by hormone therapy to maintain health. This includes treatment with estrogen, testosterone, or other hormones. Couldn’t we supplement the lost hormones in spayed or neutered dogs to treat or prevent health conditions?

One publication in eight male dogs reported treating urinary incontinence with testosterone cypionate (median dose of 1.5 mg/kg intramuscularly every 4 weeks). The treatment worked well for two dogs but was not effective in half of the dogs. However the treatment was considered safe. Other treatments for male dog incontinence include phenylpropanolamine (PPA), estrogens, surgery and anticholinergic drugs. Studies are usually small and medical therapy has not been very effective.

Research on restoring natural hormone levels in dogs after spay or neuter is generally lacking. But a recent case report provides a bit of guidance. Published in Topics in Companion Animal Medicine, this study reviewed the use of hormone restoration therapy in a neutered male dog that had significant health issues shortly after gonadectomy received at seven months of age. Weight gain, loss of mobility due to pain in the right hip, and debilitating fear of strangers significantly reduced the dog’s quality of life.

After three years of standard medical treatments with no significant improvement, hormone restoration was attempted when the dog was about 4 years old. Low testosterone was increased with injectable testosterone cypionate and a weekly subcutaneous dose (0.5 mg/kg) was found to provide a steadier level than a monthly dose. But this dog also had extremely high luteinizing hormone (LH) levels that did not come down to the normal range with testosterone alone. The use of a gonadatropin-releasing hormone agonist implant (deslorelin) effectively reduced LH levels.

Within months, this treatment resulted in improved mobility, stabilized weight, and  reduction in fear and anxiety. The dog could run, jump, and visit public parks  – things he could not do previously without pain or extreme anxiety. He also accepted the weekly injections happily with positive reinforcement training.

The Parsemus Foundation is often contacted by concerned pet owners seeking to get hormone therapy for their dog. They are often surprised to find that the dog featured in the case study is actually my own pet, Toby. Toby was adopted from a county shelter at 7 months of age and was mandatorily neutered. He showed signs of serious health problems shortly after. As an animal welfare scientist, I knew that his ailments might be due to loss of hormones from being neutered. We now call this “spay-neuter syndrome”. I researched hormone treatments and worked with Dr. Michelle Kutzler to develop a plan.
I’m thrilled that the hormone restoration treatment was successful! Toby has now been on the treatment for 5 years. His mobility problems were totally solved, and while he is still shy around strangers, his anxious behavior is manageable.”

Linda Brent, PhD
Executive Director of the Parsemus Foundation

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Last updated on February 21, 2025