The Unsolved Equation: Why Conventional Spay and Neuter Procedures Disrupts Canine Health — and What We Can Do About It

My dog Pax was two years old when I neutered him. He was a young, athletic dog — strong, eager, full of life — and I made the decision for all the reasons we, veterinarians, have given pet owners for decades: it was the responsible thing to do. “Dogs are better off, healthier and less frustrated when neutered.”

What I did not expect was what came next.

Within months, Pax started getting injured. First, it was an occasional lameness, which developed into one injury after another. Eventually, a young dog who should have been in peak condition became chronically lame.

He also began overheating at night, abandoning his bed for the cool bathroom tiles, panting more often than before. His muscles diminished and softened. His coat dulled and became shorter. The joy and spark that had defined him, that eagerness to work, to play, to engage faded unexpectedly.

I did what any veterinarian would do. I did my best and treated what I could see. I pursued rehabilitation, anti-inflammatory protocols. I tried, everything in my clinical toolkit. None of it worked in any lasting way. Pax would improve briefly and then break down again. I was just about to scheduling platelet-rich plasma therapy when the specialist's three month waitlist gave me something I thought I  had not had: time.

Time to stop trying and start searching.

It did not occur to me, not initially that the metabolic absence of testosterone and the chronic elevation of luteinizing hormone could be the root cause of what I was seeing. I was trained to think of neutering as a solved question, a net positive, a procedure with no meaningful systemic consequences. It simply was not on my diagnostic radar.

But the more I searched, the more the evidence converged on a conclusion I could not ignore: spaying and neutering could be the cause of my own dog's deterioration.

My search lead me to the discovery of the work of two researchers who would fundamentally change how I practice veterinary medicine: Dr. Linda Brent of the Parsemus Foundation and Dr. Michelle Kutzler at Oregon State University. I am deeply grateful for their contributions and also for the contribution of other researchers. Without their efforts, their willingness to challenge orthodoxy, and their generosity in sharing their clinical frameworks, Pax's story would have ended very differently. And this article would not exist.

What I found did not just challenge conventional wisdom. It indicted it.

How a Medical Procedure Became a Cultural Ritual

To understand why we are here, we need to go back to where this started. The routine surgical removal of sex organs in companion dogs is not an ancient medical tradition validated by centuries of evidence. It is a practice that originated in surgical convenience.

Dr. Karen Becker, DVM, one of the leading integrative veterinarians in North America, traced the precedent to Iowa State College of Veterinary Medicine — often cited as the first veterinary college in the world, founded in 1895.

As anesthesia became available in the early twentieth century and dog overpopulation became a genuine urban crisis, spay and neuter was promoted as the humane solution. The profession built a supporting narrative: spaying before first heat prevents mammary cancer; neutering reduces aggression and roaming; removing the gonads is simply better for domestic dogs. These claims were taught as fact in veterinary schools across North America and other parts of the world, and passed from generation to generation, from veterinarians to dog guardians.

Today, 64% of dogs in the United States are surgically sterilized — most commonly between six weeks and twelve months of age (Kutzler, 2020). In thirty U.S. states, it is legally mandated for any dog adopted from a shelter. It has become so normalized that many owners do not even register it as a medical decision. It is simply what you do.

What the profession failed to ask — for nearly a century — was what happens to the rest of the body when you permanently remove the organs that produce its primary gonadal hormones.

We are now getting the answer, and it is not comfortable.

What Happens When You Break the Feedback Loop

Lets review the hypothalamus-pituitary-gonad endocrine circuitry:

The hypothalamus, a small but extraordinarily powerful region at the base of the brain, converts sensory inputs into hormonal signals that are further passed on to the pituitary gland — the body's master endocrine controller. The pituitary responds by releasing luteinizing hormone (LH), which travels through the bloodstream to the gonads, instructing them to produce testosterone, estrogen, and progesterone. Those hormones then circle back and signal the pituitary: enough. The loop closes. LH production drops. Balance is maintained.

I sometimes compare the effect of conventional gonadectomy as the "leaky toilet" effect. In a properly functioning toilet, the rising water lifts the floater and cuts off the flow. In a properly functioning endocrine system, rising sex hormones cut off LH production. Remove the gonads, however, and the tank is perpetually empty. The floater never rises. LH keeps flooding into the body — not in the pulsatile surges of a normal reproductive cycle, but continuously, relentlessly, at concentrations much greater than the body was designed to handle.

Dr. Michelle Kutzler, DVM, PhD, a board-certified veterinary theriogenologist and a professor at Oregon State University, has spent more than a decade quantifying exactly what this means. Her research, published across multiple peer-reviewed journals, reveals a picture that should alarm every veterinarian who has ever assumed gonadectomy is a benign procedure.

In gonadectomized dogs, LH concentrations are more than 30 times higher than in normal adult dogs — and can reach levels up to 100 ng/mL compared to less than 1 ng/mL in intact animals (Kutzler, 2020; Kutzler, 2022). These are not slightly elevated levels. They are astronomical, sustained floods of a hormone that has been flooding tissues where it has no business flooding.

Here is the critical discovery: LH receptors are not confined to the reproductive organs. They have been found in virtually every tissue in the body — the thyroid gland, adrenal glands, gastrointestinal tract, cranial cruciate ligament, joint cartilage, bone, lymphocytes, blood vessels, hippocampus, lower urinary tract, and skin (Kutzler, 2020). When those receptors are chronically bombarded by supraphysiologic LH concentrations, the result is not a reproductive problem. It is a systemic, whole-body inflammatory cascade that touches every organ system simultaneously.

This is not a theory. It is a mechanism now documented in published, peer-reviewed literature. Through desexing, we have unintentionally created preventable diseases in our most beloved animals.

What the Data Shows

The list of conditions occurring at higher rates in spayed and neutered dogs has grown steadily as researchers have followed the evidence. This is not advocacy or opinion. These are published findings from peer-reviewed studies in major veterinary journals.

Cancer

The cancer data is where the picture becomes starkest. Gonads are not merely reproductive organs — they are, as Dr. Kutzler writes in her landmark 2022 paper in Theriogenology, "necessary endocrine glands for normal metabolic, endocrinologic, musculoskeletal, and anti-neoplastic health." Remove them, and the body's natural cancer defense is compromised at multiple levels simultaneously.

Hemangiosarcoma that kills most dogs within months of diagnosis — occurs at 2 to 10 times the rate in spayed females compared to intact females (Kutzler, 2022). The cardiac form specifically is five times more common. This is not a marginal statistical signal. A large case-control study of over 2 million dogs in the Veterinary Medical Database confirmed significantly elevated hemangiosarcoma risk in both spayed females and castrated males (Hahn et al., 2020). Kutzler's laboratory has gone further: when hemangiosarcoma cell lines are exposed to LH in culture, they proliferate (Zwida & Kutzler, 2022). The hormone is not merely correlated with the tumor — it appears to feed it.

Lymphoma is 3 to 4 times more common following gonadectomy in the general dog population (Kutzler, 2022). In male Golden Retrievers neutered before 12 months, the lymphoma rate is triple that of intact males — approximately one in ten develops the disease (Torres de la Riva et al., 2013). Kutzler's group has shown that up to 45% of isolated neoplastic T-lymphocytes express LH receptors, and that LH receptor activation increases their proliferation, adhesion, and invasiveness (Maxwell et al., 2024; Ettinger et al., 2019). Again: the mechanism is documented.

Prostate cancer presents a counterintuitive reversal of what veterinarians were taught. Castration was long believed to protect against prostate cancer in dogs. In fact, the opposite is true: neutered male dogs have approximately four times the rate of prostate adenocarcinoma compared to intact males (Bryan et al., 2007; Teske et al., 2002). This is one of the most thoroughly documented reversals in small animal oncology.

Note: The above is supported by the finding of a human study at Duke university (2024) that revealed that high testosterone inhibits cancer cell growth by forcing the androgen receptor into a tumor-suppressing configuration. A 2026 PubMed review stated that "Testosterone does not drive prostate cancer."

The saturation model explains that once androgen receptors are saturated, more testosterone may actually halt cancer growth — a mechanism confirmed by Bipolar Androgen Therapy (BAT) trials.

A 2025 Nature scoping review of 12 studies concluded that testosterone replacement therapy "was not associated with increased risk of cancer recurrence or progression." The original fear, traced to a single patient case from 1941, has persisted for generations without robust supporting evidence.

Osteosarcoma risk increases in dogs neutered before one year of age, particularly in large and giant breeds. In Rottweilers — already predisposed — males and females spayed or neutered before their first birthday had 3.8 and 3.1 times the bone cancer risk, respectively, compared to intact dogs (Cooley et al., 2002).

Orthopeadic Disease

The musculoskeletal consequences of early gonadectomy begin in the growth plates. Sex hormones — particularly estrogen — are required for the timely closure of physeal growth plates. Remove them before puberty, and the plates stay open longer, driving prolonged bone elongation, altered tibial plateau angles, and joint conformation problems that predispose dogs to degenerative disease throughout their lives.

Cranial cruciate ligament (CCL) rupture — one of the most common and expensive orthopedic surgeries in veterinary medicine — is twice as prevalent in spayed and neutered dogs as in intact animals (Kutzler, 2020). A 2024 systematic review and meta-analysis confirmed this association with moderate certainty across the literature, particularly in dogs gonadectomized at or before one year of age (Proteasa et al., 2024). In intact Golden Retrievers, Torres de la Riva et al. (2013) found zero cases of CCL disease, while  among early-neutered males and females, the rates were 5% and 8%, respectively.

Hip dysplasia risk increases 1.5 to 2 times, with the effect strongest in neutered males (Kutzler, 2020). In Labrador and Golden Retrievers neutered before six months, joint disorder incidence doubled and quadrupled, respectively, compared to intact dogs (Hart et al., 2014).

Metabolic and Endocrine Disruption

Gonadectomy is the single largest risk factor for obesity in dogs. Up to 68% of spayed and neutered dogs become obese (Kutzler, 2020). Food intake increases by 20% within one week of surgery and this hyperphagia persists indefinitely — not because the dog is gluttonous, but because the metabolic hormones that regulate satiety and energy expenditure have been surgically disrupted.

Gonadectomy also doubles the risk of diabetes mellitus independent of obesity, and spayed and neutered dogs develop hypothyroidism 30% more often than intact dogs (Kutzler, 2020; 2022).

The thyroid connection deserves specific attention. LH receptors are co-localized with TSH receptors on canine thyrocytes. When LH floods these receptors chronically, it interferes with normal thyroid hormone conversion T4-to-T3 which results in low T3 while T4 and TSH are normal.

This explains why so many neutered dogs display symptoms of hypothyroidism despite their T4 and TSH being normal.

Behavioral and Cognitive Consequences

The behavioral effects of gonadectomy are poorly understood by most practitioners — partly because they are difficult to attribute to a surgery performed months or years before behavioral problems present, and partly because the profession's teaching was that neutering reduces problem behavior. The evidence now points the other direction.

Estrogen and testosterone are essential precursors to dopamine synthesis. Remove them, and dopamine production drops substantially. Naturally, we must ask, how does that affect overall well-being and happiness?

The answer, increasingly documented, is: significantly. Neutered dogs have been shown in published studies to be more aggressive and fearful than intact dogs — the precise opposite of what we were taught. LH receptors in the amygdala and other limbic structures, when chronically activated by supraphysiologic LH, drive nerve inflammation. Cognitive dysfunction syndrome — the canine equivalent of Alzheimer's disease — occurs at higher rates in gonadectomized dogs (Kutzler, 2016).

The veterinary profession paradigm are shifting

In May 2024, the World Small Animal Veterinary Association (WSAVA) published its first-ever Global Guidelines for the Control of Reproduction in Dogs and Cats in the Journal of Small Animal Practice.

The WSAVA guidelines, developed by an international committee of veterinary reproductive specialists, explicitly moved away from the conventional approach of routine gonadectomy for all owned animals. They endorsed ovary-sparing spay (hysterectomy) and vasectomy as legitimate, recommended alternatives, particularly for breeds prone to the health detriments documented in the literature. They also recommended against prepubertal gonadectomy, and acknowledged that, for responsible pet owners, keeping a dog hormonally intact is a valid choice.

For those of us who have been advocating for this science, the WSAVA shift is validation. For the profession at large, it represents an institutional admission that the calculus of harm and benefit has changed — and that the old assumptions cannot hold.

And yet only 2 of 38 veterinary schools in the United States and Canada offer any instruction in alternative sterilization techniques. The gap between what the evidence now supports and what the veterinary profession teaches and practices is vast. Dr. Michelle Kutzler's own survey at AVMA annual meetings in 2017 and 2018 found that while 73% of veterinarians discussed the long-term health risks of spay/neuter with clients, only 7% offered any alternative procedure (EurekAlert, 2018).

The knowledge is there. The behavior has not caught up.

The Solution: Hormone Replacement Therapy

For the millions of dogs already spayed or neutered — including my own dog Pax — the question is not theoretical. The gonads are gone. What can be done?

The answer emerging from clinical practice and early research is hormone replacement therapy (HRT): restoring sex hormones to physiologic levels and, critically, reducing the chronic LH elevation that drives so much downstream damage.

The first published case report of hormone restoration in a castrated dog appeared in 2021 in Topics in Companion Animal Medicine, authored by Dr. Linda Brent, PhD (Executive Director of the Parsemus Foundation), Elaine Lissner, and Dr. Michelle Kutzler (Brent et al., 2021). The subject was Toby — Dr. Brent's own dog, adopted from a county shelter at seven months and mandatorily neutered. Within months, Toby developed rapid weight gain, loss of mobility from right hip pain, and debilitating fear of strangers. Three years of standard veterinary treatment — pain medication, joint supplements, thyroxine, antidepressant — produced minimal improvement. He was essentially housebound from anxiety.

When Dr. Brent and Dr. Kutzler initiated hormone restoration, Toby's trajectory reversed. His protocol combined weekly subcutaneous testosterone cypionate injections at 0.5 mg/kg with a deslorelin acetate (Suprelorin) implant to suppress the chronically elevated LH. Within months, his mobility returned. His weight stabilized. His fear and anxiety became manageable. He could run, jump, and visit public parks. As of 2024, Toby has been on the protocol for over five years — and continues to thrive.

The protocol I have used for my dog Pax follows the same framework:

Component 1 — Testosterone Replacement:

Testosterone cypionate, administered weekly by subcutaneous injection at 0.5 mg/kg. Weekly dosing is essential — monthly injections at higher doses create hormonal roller-coaster patterns that are destabilizing rather than therapeutic. The first target-animal safety study of this protocol, published in BMC Veterinary Research in July 2025 (Brent et al., 2025), confirmed that weekly injectable testosterone was safe in neutered dogs across all tested doses over 90 days.

Component 2 — LH Suppression: 

A Suprelorin (deslorelin acetate) implant, placed subcutaneously every six months. This GnRH agonist initially causes a brief LH surge before desensitizing the pituitary and suppressing LH production. Testosterone supplementation alone does not normalize LH at the above recommended doses  — the implant is necessary to address the inflammatory component of the syndrome.

My personal experience with Pax and several other patients ranging from the age of 2 to 18 has also been overwhelmingly positive with no clear evidence of undesirable side effects. The results are undeniable. 

Muscle mass recovered. Coat quality returned. Injuries stopped. Energy and engagement came back. Most significantly: the spark and personality returned.

Pax's transformation brought his joy of life back. He is happy, alert, he wants to work and play, and wants to be engaged.

That joy of life is not a subjective impression. It is the observable manifestation of a brain receiving adequate dopamine, a musculoskeletal system receiving its anabolic support, an immune system no longer being chronically dysregulated by LH flooding.

Protocols for Female Dogs

The female protocol is less standardized than the male, which requires acknowledgment. The research base for female HRT in dogs is thinner, and the optimal combination of estrogen, testosterone, and LH suppression remains an active area of investigation. Dr. Kutzler's suggests estriol or diethylstilbestrol (a type of estrogen) 0.5 - 1 mg per dog/ day, combined weekly testosterone 0.25mg/kg, and Suprelorin implant every six months.

Both estrogen and testosterone are important in females — females actually produce more testosterone by quantity than estrogen, and testosterone plays essential roles in muscle strength and mental health. Some veterinarians now use low-dose testosterone in spayed females with musculoskeletal problems and performance dogs with repeated injuries, with meaningful clinical results.

Many practitioners would welcome the ability to document the degree of LH elevation and track response. Colorado State University's Veterinary Endocrinology Laboratory used to offer LH testing but the lab is no longer offering this test due to the lack of interest at the time of writing this article.

That said, any dog spayed or neutered for more than six months can be assumed to have markedly elevated LH; this is why testing before initiating therapy is not as important in patient assessment as the clinical symptoms in conventionally neutered and spayed patients.

Prevention: The Better Path

The optimal intervention, of course, is not hormone restoration but prevention — keeping sex glands intact while eliminating the risk of unwanted reproduction is the most viable option for rescue organizations and shelters.

Two surgical approaches accomplish this.

1. Ovary-Sparing Spay (Hysterectomy): The uterus is removed while both ovaries are preserved. This eliminates the risks of pregnancy and pyometra while maintaining full ovarian hormone production. The ovaries — not the uterus — are responsible for more than 98% of sex hormone synthesis. A hysterectomized female continues normal estrous cycles (behavioral signs, vulval changes) but cannot become pregnant and will not have bloody discharge. Dr. Kutzler has been performing and teaching this procedure since 2011, when she produced the first instructional video in partnership with the Parsemus Foundation. The WSAVA 2024 guidelines explicitly recommend it as a legitimate alternative.

   Dr. Stefano Romagnoli, one of the leaders in the field, has moved hormone‑sparing reproductive control into the mainstream by leading the first global guidelines on the topic. As chair of the WSAVA Reproduction Control Committee and lead author of the 2024 WSAVA guidelines for the control of reproduction in dogs and cats, he helped formalize ovary‑sparing spays, vasectomies, and GnRH‑agonist implants as evidence‑based alternatives to traditional gonadectomy, rather than fringe procedures.Those guidelines explicitly emphasize choosing methods “with the least long‑term health concerns” and state that, particularly in large and giant‑breed dogs, hormone‑sparing options like vasectomy and ovary‑sparing surgery should be offered.

   Some veterinarians and shelters have expressed their concerns over the amount of time hormone sparing ovariectomy requires. However, Dr. Maricel Lichuan has performed thousands of flank approach surgeries in the Philippines, which based on her reports do not require additional time in comparison with conventional spay.

2. Vasectomy severs the vas deferens, preventing sperm transport while leaving the testes fully intact. The dog retains complete testosterone production and all secondary sex characteristics. Sperm is absent from the ejaculate within 24 hours (Kutzler, 2020). Once again, Dr. Lichuan has performed hormone-sparing sterilizations at scale, reporting that vasectomy can be completed in the same time or less than a traditional neuter once the technique is mastered. The AVMA recognizes both vasectomy and hysterectomy as acceptable sterilization methods.

The barriers to adoption of these techniques are structural rather than scientific. They are not taught in veterinary school. They require learning a new surgical approach without mentorship. And the shelter system — constrained by state mandates, high surgical volume, and institutional inertia — has been almost entirely resistant to change.

This is something that we all need to work on changing.

The Research Driving Change

Behind every major scientific advance is someone willing to ask the question the field has decided not to ask:

Dr. Michelle Kutzler is the scientist who cracked the mechanism open. Her 2020 paper in Animals — "Possible Relationship between Long-Term Adverse Health Effects of Gonad-Removing Surgical Sterilization and Luteinizing Hormone in Dogs" — synthesized the LH hypothesis for the first time and documented the distribution of LH receptors throughout virtually every tissue in the body. Her 2022 Theriogenology paper extended this to cancer biology, demonstrating that LH receptor activation drives proliferation in hemangiosarcoma and lymphoma cell lines. Her laboratory continues to investigate whether GnRH agonist implants might extend remission times in dogs with LH receptor-positive tumors — a potential therapeutic application of incalculable importance.

Her conclusion, published in Theriogenology in 2022, deserves to be read in every veterinary school in the world:

"Gonads should no longer be considered mere gamete-producing or ancillary sex organs but rather necessary endocrine glands for normal metabolic, endocrinologic, musculoskeletal, and anti-neoplastic health."

Dr. Linda Brent of the Parsemus Foundation has been the organizational force connecting research to clinical practice. Under her leadership, Parsemus published the first case report of hormone restoration in a neutered dog, funded and co-authored the first safety and dosing study for injectable testosterone in neutered males, built and maintains the veterinary directory of practitioners offering hormone-sparing sterilization and HRT, and has built a growing body of public-facing and peer-reviewed literature establishing the clinical and ethical framework for this approach. "The bottom line," she has said, "is that the longer dogs have their natural hormones, the healthier they are.”

As a results of this groundbreaking work, Dr. Karen Becker and I have launched HormoneHealthForDogs.org. Our goal is to translate this groundbreaking science to a broader public audience, and connect owners and veterinarians around this emerging field, fund research, and create change from the ground up. 

Where We Go From Here

Without a doubt more research is needed. The safety study published in BMC Veterinary Research by Brent et al. (2025) — the first formal target-animal safety trial for testosterone replacement in neutered dogs — involved twelve dogs over ninety days. The case literature is composed primarily of individual dogs whose outcomes Dr. Becker and I have documented alongside Dr. Brent and Dr. Kutzler. Controlled, randomized clinical trials are urgently needed. Dr. Kutzler herself has called for them explicitly.

What we do have is mechanism, coherence, and a growing number of clinical records. The mechanism — chronic LH flooding driving systemic inflammation across every tissue that carries LH receptors — is documented in multiple peer-reviewed papers with clear molecular evidence. The coherence is striking: a single hormonal disruption explains dozens of diseases that veterinary medicine has been treating in isolation for decades. And the clinical record, while not yet statistically mature, points consistently in one direction.

We have to come to terms with the fact that our profession, despite our best intention, contributed to the occurrence of degenerative diseases. We didn’t know this was the case, but now we do.

Once we know, we cannot ignore the problem. Once the mechanism is clear, the obligation to inform our clients and to act is the only way forward.

After years of clinical observation and careful engagement with this research, I strongly believe that a large proportion of chronic, degenerative conditions in veterinary practice today are directly or partially connected to the hormonal depletion that conventional spay and neuter procedures induced in otherwise healthy animals. This is supported by increasing body of research. 

For owners of dogs who have already been spayed or neutered: HRT is an option worth exploring seriously. Find a veterinarian trained in integrative or functional medicine — the Parsemus Foundation and the American Holistic Veterinary Medical Association maintain searchable directories.

For dog guardians planning sterilization: ask about ovary-sparing spay or vasectomy. Ask whether your veterinarian performs them. If the answer is no, find one who does — or ask your veterinarian to learn.

For veterinarians reading this: the WSAVA has moved. The literature is moving. The question is no longer whether gonadal hormones matter to the whole-dog health picture — they do, extensively and mechanistically. The question is what we do with that knowledge.

What I have learned from Pax, from Homer, from Toby, and other patients undergoing hormone replacement therapy is that dogs come to us equipped with a hormone system that evolved over millions of years. That architecture of this system is not incidental to their health, it is the foundation.

When we take it away — as a routine act, without conversation, without alternatives offered, without an understanding of what we are removing — we are making a decision on behalf of an animal who cannot consent, based on assumptions that the evidence is now overturning. That is a responsibility that demands better.

My dog Pax is swimming and running and hiking again. He is happy, alert, engaged, and joyful. This is also possible for millions of beloved dogs around the world.

References

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Dr. Peter Dobias, DVM, is a Czech-Canadian veterinarian, with over 35 years of clinical experience. He is the co-creator of the Hormone Health for Dogs initiative (hormonehealthfordogs.org), and founder the founder of drpeterdobias.com andHis dog Pax is the reason this article exists.