Canine Endocrinology · Sterilization Timing

Your Dog's Hormones Do More Than Control Reproduction.

For years, spaying and neutering has often been approached as a simple question of when. Modern veterinary research suggests the answer can be more nuanced.

Breed, sex, projected adult size, lifestyle, health history and timing may all matter.

Explore the EvidenceMy Dog Was Already Neutered

Independent Educational Resource • Evidence-Based • Not a Substitute for Veterinary Care

A healthy adult golden retriever standing calmly in a sunlit meadow
Sterilization timing is increasingly framed as an individualized decision.
01Why This Conversation Is Changing

The Question Is No Longer Simply "When Should I Neuter My Dog?"

Veterinary medicine has increasingly moved toward individualized decisions about sterilization timing. Current guidance recognizes that the potential benefits and risks can vary according to a dog's size, breed, sex, health and circumstances.

AAHA's canine guidance sets out different timing considerations for small and large dogs, and specifically notes that research findings differ by breed. It also cautions that the underlying studies were conducted in particular populations, which limits how widely their conclusions can be applied.

Read the Research: AAHA Spay and Neuter Timing

There Is No Single Sterilization Age That Is Ideal for Every Dog.

A reading of current AAHA canine life stage guidance.
02You Have More Than One Option

Sterilization Doesn't Have to Mean Removing the Gonads.

Most owners are presented with a single question: spay or neuter, and when. In fact, reproductive control and hormone removal are two separate things, and there is more than one way to accomplish the first.

Gonadectomy — castration in males, traditional spay or ovariectomy in females — prevents reproduction by removing the gonads, which also ends normal sex-hormone production. Gonad-sparing sterilization prevents reproduction while retaining functioning gonads and endogenous sex-hormone production.

A 2020 review specifically describes vasectomy and ovary-sparing hysterectomy as gonad-sparing approaches, and a 2023 JAVMA study evaluated health and behavioral outcomes in dogs that had undergone these procedures.

Two Different Questions

Do I need to prevent reproduction?
Nearly every household answers yes. Several procedures can achieve it.
Do I need to remove hormone production to do it?
That is a separate clinical decision, with benefits and risks in both directions.
Read the Research: Outcomes in 6,018 Owner-Reported Dogs

Gonadectomy

Castration (Male)

The testes are removed, which ends normal testicular hormone production.

Castration removes the testes. Reproduction is prevented, and the dog's primary source of testosterone is removed for the remainder of his life.

Published guidance discusses this procedure as preventing certain conditions while altering the risk profile for others, which is why timing is framed as a balance rather than a single recommended age.

Trade-Offs

  • Reproduction is prevented.
  • Normal testicular hormone production ends.
  • Testosterone-dependent conditions are largely prevented.
  • Timing may interact with skeletal, orthopedic and breed-specific considerations.

Traditional Spay or Ovariectomy (Female)

The ovaries are removed, which ends normal ovarian hormone production.

A traditional spay removes the ovaries, and in many procedures the uterus as well. Reproduction is prevented and estrous cycles end.

AAHA discusses this procedure in terms of competing benefits and risks, including reproductive considerations weighed against other long-term outcomes.

Trade-Offs

  • Reproduction is prevented.
  • Estrous cycles end.
  • Normal ovarian hormone production ends.
  • Risks in both directions are altered rather than eliminated.

Gonad-Sparing Sterilization

Vasectomy (Male)

The reproductive tract is interrupted while the testes remain in place and hormonally functional.

A vasectomy interrupts the reproductive tract while leaving the testes in place. The testes continue producing hormones, but sperm cannot normally reach the ejaculate.

A vasectomy does not provide the same health effects as castration, because testosterone production remains. Any outcome attributed to the loss of testosterone after castration should not be assumed to apply here, and neither should the conditions that castration prevents.

Trade-Offs

  • Reproductive capacity is interrupted.
  • Testosterone production remains.
  • Testosterone-dependent conditions are not prevented.
  • Prostate disease risk is not necessarily eliminated.
  • Appropriate post-procedure confirmation of sterility matters.

Ovary-Sparing Hysterectomy (Female)

The uterus is removed while the ovaries are left intact and hormonally functional.

An ovary-sparing hysterectomy removes the uterus while leaving the ovaries intact and hormonally functional. With no uterus, pregnancy cannot occur; with the ovaries retained, ovarian hormone production continues.

The dog will still experience estrous cycles because the ovaries remain functional, and she can still attract and be receptive to intact males. She simply cannot carry a normal pregnancy.

This is not the perfect alternative to spaying. It is a different reproductive strategy with different benefits and trade-offs, and several long-term questions remain open in the literature.

Trade-Offs

  • Pregnancy cannot occur.
  • Ovarian hormone production continues.
  • Estrous cycles and associated behavior continue.
  • Mammary-tumor risk is not reduced in the same way as removal of the ovaries.
  • Long-term ovarian health after the procedure requires further study.
  • Complete removal of uterine tissue matters, and stump-related disease is discussed in the literature.

No Surgical Sterilization

Remaining Intact With Reproductive Management

No surgery is performed, and reproduction is prevented through management rather than anatomy.

Keeping a dog intact is a management decision, not a lifestyle impossibility. It does, however, transfer the entire responsibility for preventing reproduction to the household.

UC Davis's breed-specific work notes that for some breeds and sexes there was no age at which sterilization showed a clear advantage for the outcomes examined, which is why leaving certain dogs intact is discussed as a reasonable option to consider with a veterinarian.

Trade-Offs

  • Endogenous sex-hormone production is fully retained.
  • Reproduction is possible unless it is actively prevented.
  • Reproductive-tract conditions associated with intact status are not prevented.
  • Households must be able to manage estrus, roaming and access to other dogs reliably.

None of these options is presented here as the correct one. Availability varies by practice, and gonad-sparing procedures require a veterinarian experienced in performing them and in confirming the intended result.

03Do I Actually Have to Remove My Dog's Hormones?

Sterilization and Gonadectomy Are Not the Same Thing.

Sterilization means reproduction is prevented. Gonadectomy means the gonads have been removed. Every gonadectomy sterilizes a dog, but not every method of sterilization removes hormone production.

OptionPrevents ReproductionGonads RetainedSex Hormones Retained
CastrationYesNoNo normal testicular production
Traditional Spay or OvariectomyYesNoNo normal ovarian production
VasectomyYesYesYes
Ovary-Sparing HysterectomyYesYesYes
Remaining IntactNo — management onlyYesYes, fully retained

The appropriate choice depends on the individual dog, reproductive-control requirements, health risks, lifestyle and the owner's ability to prevent unintended breeding.

04"I Want to Keep My Dog Intact"

Keeping a Dog Intact Is a Management Decision, Not a Lifestyle Impossibility.

It is also not effortless for every household. When anatomy is not preventing reproduction, management is. That responsibility is continuous, and it has to be realistic for the way your household actually lives.

For Male Dogs

  • Secure fencing, checked regularly for gaps and digging.
  • Consistent leash management on every walk.
  • Preventing access to females in heat, including in the household.
  • Supervision around other dogs.
  • Understanding normal mating behavior and how it escalates.
  • Responsible boarding and daycare arrangements, disclosed in advance.
  • Current identification and a registered microchip.
  • Avoiding unsupervised outdoor access.

For Female Dogs

  • Understanding the estrous cycle and tracking it in writing.
  • Keeping her securely separated from intact males during fertile periods.
  • Leash-only walks when appropriate.
  • Avoiding dog parks and daycare during heat.
  • Understanding the behavioral changes that accompany a cycle.
  • Using appropriate washable protection for discharge when needed.
  • Planning boarding and travel around heat cycles.

An intact female requires responsible reproductive management, because pregnancy can occur during estrus.

05How Often Does a Female Dog Go Into Heat?

Roughly Twice a Year — but "Every Six Months" Is Not a Rule.

Most female dogs experience estrous cycles approximately twice annually, but intervals vary substantially by individual, breed and size. Some dogs cycle three times a year; some large and giant breeds cycle less often. Young dogs may cycle irregularly at first.

Because of that variation, a calendar assumption is not a reproductive-management plan. Recording the first day of each cycle is far more useful than an average.

The Four Stages

  1. 01

    Proestrus

    Vulvar enlargement and bloody discharge.

    Males are typically attracted, but the female is generally not yet receptive.

  2. 02

    Estrus

    The receptive and fertile period.

    Discharge often becomes lighter or straw-colored as fertility rises, not heavier.

  3. 03

    Diestrus

    The hormonal phase that follows estrus.

    Progesterone dominates, whether or not the dog became pregnant.

  4. 04

    Anestrus

    The reproductive resting period between cycles.

    Cycle intervals vary substantially between individuals and breeds.

Bleeding does not necessarily mean the dog is at her most fertile. Visible discharge and peak fertility do not correspond precisely, which is why owners who rely on appearance alone are sometimes surprised by a pregnancy.

Heat Management Checklist

  • Leash walks only.
  • Secure doors and gates every time.
  • No unsupervised outdoor access.
  • No dog parks.
  • Separate from intact males.
  • Inform daycare and boarding providers.
  • Supervise interactions with other dogs.
  • Record the first day of the cycle.
  • Discuss abnormal bleeding or discharge with your veterinarian.

Never Rely on Diapers or Physical Barriers as Contraception.

Washable protection manages discharge. It does not prevent mating, and it should never be treated as a substitute for separation and supervision during a cycle.

06Common Claims vs. What the Evidence Actually Says

Most of These Claims Are Not Simply False. They Are Incomplete.

Several widely repeated statements contain a real finding wrapped in an overstatement. The useful correction is rarely "that's a myth" — it is understanding what the evidence supports and where it stops.

07Before You Spay or Neuter

Ten Questions Worth Asking Before Surgery Is Scheduled.

None of these questions is confrontational. They are the questions a thorough conversation would cover anyway, and asking them makes that conversation faster.

Open the Full Preparation Guide
  1. 01What is my dog's projected adult size?
  2. 02What does research say about this breed?
  3. 03Is there evidence that timing affects orthopedic or cancer risk in this breed?
  4. 04Does sex change the recommendation?
  5. 05What are the benefits of sterilizing now?
  6. 06What are the potential benefits of waiting?
  7. 07Are gonad-sparing options available?
  8. 08Could vasectomy or ovary-sparing hysterectomy be appropriate?
  9. 09What reproductive-management requirements would apply if we keep the dog intact?
  10. 10What does the veterinarian recommend, and what evidence supports that recommendation?
08What Happens When the Gonads Are Removed?

Reproduction Isn't the Only Thing That Changes.

The ovaries and testes are reproductive organs, but they are also the body's primary source of sex hormones. Surgical sterilization removes those organs, which changes the dog's reproductive hormone environment for the remainder of its life.

Because these hormones have physiological effects beyond reproduction, researchers have investigated how the timing of gonadectomy may relate to skeletal development, orthopedic disease, body composition, metabolic and endocrine health, certain cancers, urinary health and other outcomes.

How to Read This Research

Research has identified associations between sterilization status or timing and certain health outcomes in some populations of dogs. The magnitude and direction of these associations vary by breed, sex, size and age.

That is a deliberately careful sentence. It is not the same as saying that removing the gonads causes these diseases — a claim the current literature does not support.

09What Does the Research Actually Show?

Four Areas Where the Evidence Is Most Often Discussed.

Researched / Breed- and Size-Dependent

Skeletal & Orthopedic Health

Gonadal sex hormones participate in skeletal maturation, including the timing of growth-plate closure. Because of this, researchers have examined whether the age at which the gonads are removed relates to later orthopedic outcomes.

Studies from UC Davis have reported associations between earlier sterilization and higher observed rates of certain joint disorders in some breeds — findings that appear most relevant in larger dogs and that are not consistent across every breed studied.

UC Davis — Identifying When a Dog Should Be Spayed or NeuteredUC Davis Veterinary Medicine — Spaying or Neutering Your Dog

Researched / Highly Breed- and Sex-Specific

Cancer

Sterilization status and timing have been associated with differences in the observed frequency of certain cancers in some breeds and sexes. These findings are not uniform: in the UC Davis breed-specific work, several breeds showed no meaningful difference at any age examined, while others showed differences in one sex only.

Nothing in this literature supports the statement that early neutering universally causes cancer. Direction and magnitude both vary by population.

UC Davis — Breed-Specific Findings

Incorporated Into Current Veterinary Guidance

Growth & Development

Skeletal maturation occurs on different timelines in different breeds and sizes. Small dogs finish growing considerably earlier than large and giant breeds.

AAHA's canine guidance reflects this directly: it discusses later timing for large-breed dogs, generally after growth has stopped, and different considerations for small dogs.

AAHA — Spay and Neuter Timing

Both Directions Carry Risk

Competing Risks

Delaying sterilization is not automatically the safer choice. In females, a longer intact period means more exposure to reproductive risks, including unwanted pregnancy and, with successive heat cycles, mammary neoplasia risk that earlier spaying may reduce.

The decision is therefore about balancing competing risks, not eliminating risk. AAHA frames it the same way.

AAHA — Balancing Risks
10Breed Matters

One Breed's Research Cannot Automatically Be Applied to Another.

UC Davis research examining more than 40 breeds has demonstrated substantial variation between them. Some breeds showed differences in joint disorders or cancers associated with the age at sterilization; others showed no significant differences at any age examined.

A finding observed in Golden Retrievers does not automatically apply to a Labrador Retriever, a Great Dane, a Chihuahua or a mixed-breed dog. Sex frequently matters as well: within a single breed, the pattern reported for males may differ from the pattern reported for females.

UC Davis — Breed-Specific Sterilization ResearchUC Davis Veterinary Medicine — When Should You Neuter or Spay Your Dog?
A large-breed dog and a small terrier sitting side by side outdoors
Illustrative of how breed-specific research is structured. These are not medical predictions for an individual dog.
Breed ProfileSexTiming StudiedWhat Researchers Reported
Large, slow-maturing breedMaleUnder 12 monthsHigher observed joint-disorder rates in some breeds; not all
Large, slow-maturing breedFemaleUnder 12 monthsBreed-dependent differences; in several breeds, none observed
Small breedEitherAround 6 monthsJoint-disorder differences generally not observed in the small breeds studied
Mixed breedEitherVariesStudied by weight category rather than breed; findings varied by size
11When Should My Dog Be Spayed or Neutered?

There Isn't One Correct Age.

The figures below summarize the general timing considerations discussed in AAHA's canine guidance. They are a starting point for a conversation, not a prescription.

Smaller Dogs

Male

Approximately 6 Months

Female

Approximately 5–6 Months

Before the anticipated first heat.

Larger Dogs

Male

Approximately 9–15 Months

Generally after growth has stopped.

Female

Approximately 5–15 Months

More individualized; depends on the balance of risks.

These Are Guidelines, Not Universal Rules.

AAHA specifically recommends individualizing the decision according to breed, projected adult size, health risks and the dog's circumstances — including the household's ability to manage an intact dog responsibly.

AAHA — Spay and Neuter Timing
12Before You Schedule the Surgery

Ask Better Questions Before Making the Decision.

Your veterinarian knows your dog. This list is simply intended to make the conversation more specific — and to make sure the factors current research considers relevant are on the table.

This site does not provide individualized medical recommendations.

  1. 01What does the research say about my dog's breed?
  2. 02How does projected adult size affect timing?
  3. 03When is my dog's expected skeletal maturity?
  4. 04Are there breed-specific orthopedic risks?
  5. 05Are there breed-specific cancer considerations?
  6. 06What are the benefits of sterilizing now?
  7. 07What are the potential benefits of waiting?
  8. 08What reproductive-control options exist while we wait?
  9. 09How does my dog's lifestyle affect the decision?
  10. 10What factors are you using to determine your recommendation?
13If Your Dog Was Already Neutered Early

If It Already Happened, Don't Panic.

Early sterilization does not mean that your dog will necessarily develop a health problem. Research of this kind describes population-level associations and changes in risk. It cannot predict the future health of an individual dog.

AAHA states the caution plainly in its own guidance: association does not establish cause and effect.

AAHA — Concepts to Consider
A mixed-breed dog resting calmly on a linen blanket in soft daylight

What You Can Do Now

Keep a simple record. Useful, specific information helps a veterinarian interpret anything that comes up later.

  • Age at sterilization
  • Breed
  • Sex
  • Expected adult size
  • Current age
  • Weight
  • Body condition
  • Mobility
  • Orthopedic history
  • Relevant medical history
  • Current medications
  • Changes in activity or behavior

Health concerns should be evaluated by a veterinarian rather than automatically attributed to sterilization. Many conditions share overlapping signs, and attributing them to one cause can delay an accurate diagnosis.

14Quality of Life

Pay Attention to the Whole Dog.

Owners often notice changes long before a clinical test does. Observing these areas over time gives a veterinarian better information to work with.

  • Activity
  • Strength
  • Muscle condition
  • Mobility
  • Willingness to exercise
  • Body condition
  • Behavior
  • Appetite
  • Sleep
  • Urinary health
  • General vitality

These observations are not diagnostic indicators of hormone deficiency. They are simply useful information to discuss with a veterinarian.

09The Emerging Science of Hormone Restoration

Could Hormone Restoration Become Part of Veterinary Medicine?

This is one of the most interesting emerging questions in canine health. Surgical gonadectomy removes the primary source of gonadal sex hormones. Researchers are now beginning to investigate whether carefully controlled hormone replacement could be appropriate for some neutered dogs.

It is important to be precise about where this stands. This is a research question, not an established treatment. No veterinary guideline currently recommends routine hormone replacement in neutered dogs, and the published work to date is small in both sample size and duration.

Status

Emerging Research

This site explains what has been studied and what has not. It does not provide doses, schedules, concentrations, administration instructions, or advice to start, stop or change any therapy.

10 · What Research Has Been Done?

The Research Is Beginning — But It Is Still Early.

A peer-reviewed case report published in 2021 described a neutered male dog that received testosterone cypionate, with the authors reporting improvements including muscle mass, mobility and other clinical observations.

Case Report — Very Low Level of Evidence

A single case cannot establish that testosterone caused the improvements, or that the same outcome would occur in other dogs. Case reports generate hypotheses; they do not test them. There was no control, no blinding and no comparison group.

11 · The 2025 Testosterone Study

A New Step: Testosterone Dosing and Safety Research

A 2025 peer-reviewed study investigated testosterone cypionate administration in neutered male dogs.

  • 12 neutered male dogs
  • Testosterone cypionate
  • Multiple dosage groups
  • 90-day study period
  • Testosterone concentrations increased in a dose-dependent manner
  • The study investigated safety and dosing

The study did not establish long-term clinical benefits. The sample size was small, the duration was short, and further research is needed. Nothing in it implies that testosterone therapy is currently recommended for routine use in neutered dogs.

Early Clinical Research — Not Established Therapy

Find the Peer-Reviewed Publication on PubMed
18What Could the Future Look Like?

Potential Future Options

Veterinary reproductive medicine is becoming more individualized. These are open research directions — described here as questions, because that is what they currently are.

01

Physiological Hormone Restoration

Could future protocols restore hormone concentrations to physiologically appropriate ranges in selected neutered dogs?

Status — Under Research

02

Individualized Hormone Monitoring

Could future veterinary protocols use laboratory testing and clinical measurements to identify dogs who might benefit?

Status — Not Yet Established

03

Non-Surgical Sterilization

Could future reproductive-control technologies prevent reproduction without permanently removing gonadal hormone production?

Status — Research / Developing Technologies

04

Breed-Specific Reproductive Medicine

Could sterilization decisions become increasingly individualized according to breed, sex, genetics and health profile?

Status — Already Increasingly Reflected in Research and Guidelines

WSAVA — 2024 Reproduction Control Guidelines
19What We Know vs What We Don't Know

Good Science Includes Knowing What We Don't Know.

What We Know

  • Gonadectomy changes reproductive hormone production.
  • Sterilization timing is associated with different health outcomes in some populations of dogs.
  • Breed and sex can substantially modify the observed risks.
  • Body size is relevant to orthopedic outcomes.
  • Veterinary organizations increasingly emphasize individualized decision-making.
  • Testosterone administration can raise circulating testosterone in neutered male dogs under studied conditions.

What We Don't Know Yet

  • Which dogs would actually benefit from long-term hormone restoration.
  • Whether testosterone replacement improves long-term health outcomes.
  • Whether hormone restoration prevents orthopedic disease.
  • Whether it changes cancer risk.
  • Whether it improves longevity.
  • The optimal long-term testosterone concentration.
  • The ideal dose and treatment schedule.
  • Which dogs are most likely to benefit.
  • The long-term risks of treatment.
20Avoiding False Certainty

Correlation Is Not Causation.

If a study finds that dogs neutered earlier experienced a particular disease more frequently, that does not automatically prove that neutering caused the disease.

Dogs neutered at different ages may also differ in breed, size, genetics, lifestyle, activity, body condition, diet, environment and the reasons their owners chose that timing. Any of those factors can influence the outcome being measured. Careful researchers account for what they can and are explicit about what they cannot.

This is not a technicality. It is the difference between information that helps an owner make a decision and a claim that sounds certain but is not.

AAHA — Concepts to Consider
21Testing & Diagnostics

Understand the Tests.

Good questions start with good information.

Many canine endocrine and metabolic conditions have overlapping symptoms. Fatigue, weakness, weight change, muscle loss, changes in appetite, increased thirst, changes in urination, skin and coat changes, exercise intolerance, collapse and even seizures can each have many possible causes.

The purpose of this section is not to tell you what disease your dog has. It is to help you understand what diagnostic testing exists, why particular tests may be appropriate for particular clinical presentations, and how to have a more productive conversation with your veterinarian.

What This Section Helps You Understand

  • What types of diagnostic testing exist.
  • Why certain tests may be appropriate for certain clinical presentations.
  • What questions to ask your veterinarian.
  • When a specialist may be appropriate.
  • How veterinary diagnostic laboratories work.
  • How owners may be able to access independent veterinary diagnostic laboratories through their veterinarian.

Important Safety Principle

This website never says: "You have these symptoms, so you need these tests."

It says: "These symptoms can have multiple causes. These are tests you may wish to discuss with your veterinarian." Every symptom-based prompt here is a conversation starter, not a diagnostic prescription.

What This Site Will Not Do

  • It will never diagnose your dog.
  • It will never provide treatment instructions.
  • It will never recommend changing or stopping a medication.
  • It will never interpret an individual laboratory result.
22The Ideal Journey

Better Informed, Without Practicing Medicine.

This is the central philosophy of the diagnostic portion of this website. Each step belongs to the owner or the veterinarian — and the order matters.

  1. 01

    Notice a problem.

  2. 02

    Learn what conditions can overlap.

  3. 03

    Understand what evidence exists.

  4. 04

    Learn what tests exist.

  5. 05

    Discuss appropriate testing with your veterinarian.

  6. 06

    Use a qualified veterinary diagnostic laboratory where appropriate.

  7. 07

    Interpret results with your veterinarian.

  8. 08

    Consider treatment only when clinically justified.

23Diagnostic Laboratories

Your Veterinarian Draws the Blood. The Laboratory Does the Testing.

Veterinary practices may use commercial reference laboratories or university veterinary diagnostic laboratories. In some circumstances, a veterinarian may be able to collect the appropriate specimen and submit it to another qualified veterinary diagnostic laboratory instead of the practice's default.

This is a question to raise with your veterinarian, not a decision to make around them. Sample type, handling and shipping requirements vary by test, and the laboratory's current instructions govern.

Potential Advantages

  • Access to specialized endocrine assays.
  • University veterinary diagnostic expertise.
  • Transparent laboratory pricing.
  • Access to tests not routinely offered by a local clinic.
  • Direct laboratory consultation in some settings.

Read This Before Assuming You Will Save Money

Laboratory pricing does not necessarily equal total diagnostic cost.

Owners may also pay for veterinary examination, blood collection, sample processing, shipping, interpretation, follow-up consultation and repeat testing. Independent laboratories are not always cheaper, and this website does not claim they are.

Why There Is No "Cheapest Lab" Ranking

Ranking laboratories by price would require current prices that have been independently verified and dated. Instead, this directory reports what each laboratory's own website confirms, links directly to its current fee schedule and specimen requirements, and records when the entry was last verified.

Veterinary Diagnostic Laboratories

This directory includes only laboratories whose own websites confirm the relevant services. It is reviewed periodically because laboratory policies and fees change.

Cornell Animal Health Diagnostic Center — Endocrinology

New York · Last Verified August 2026

Cornell's endocrinology laboratory provides veterinary endocrine testing for dogs, including specialized hormone and vitamin assays, and states that it offers pre-testing advice and consultation on results.

Endocrinology testing and consultationAdrenal and pituitary function test protocols

Required — your veterinarian collects and submits the specimen. Sample type, handling and shipping requirements vary by test; your veterinarian should follow the laboratory's current instructions. Availability, fees and specimen requirements can change — always verify current information directly with the laboratory.

UC Davis Clinical Endocrinology Laboratory

California · Last Verified August 2026

The UC Davis Clinical Endocrinology Laboratory serves veterinarians and owners and performs hormonal assays, with particular strength in reproductive hormone testing.

Current testing fees and submission instructionsSubmission and specimen requirements

Veterinary involvement expected for collection, handling and interpretation. Sample type, handling and shipping requirements vary by test; your veterinarian should follow the laboratory's current instructions. Availability, fees and specimen requirements can change — always verify current information directly with the laboratory.

Michigan State University Veterinary Diagnostic Laboratory — Endocrinology

Michigan · Last Verified August 2026

MSU's endocrinology laboratory provides canine endocrine testing, including thyroid and adrenal testing along with other specialized assays.

Current test catalog and feesTest catalog specimen requirements

Required — submitted through a veterinarian. Sample type, handling and shipping requirements vary by test; your veterinarian should follow the laboratory's current instructions. Availability, fees and specimen requirements can change — always verify current information directly with the laboratory.

LaboratoryStateEndocrinologyThyroidAdrenalReproductive HormonesDirect Owner AccessVeterinary SubmissionCurrent FeesSpecimen RequirementsLast Verified
Cornell Animal Health Diagnostic Center — EndocrinologyCornell AHDC↗New YorkYesYesYesYesVeterinary submission / confirm with laboratoryRequired — your veterinarian collects and submits the specimen.Endocrinology testing and consultation ↗Adrenal and pituitary function test protocols ↗August 2026
UC Davis Clinical Endocrinology LaboratoryUC Davis↗CaliforniaYes——YesLaboratory states it serves veterinarians and owners — confirm current policyVeterinary involvement expected for collection, handling and interpretation.Current testing fees and submission instructions ↗Submission and specimen requirements ↗August 2026
Michigan State University Veterinary Diagnostic Laboratory — EndocrinologyMichigan State University↗MichiganYesYesYesYesVeterinary submission / confirm with laboratoryRequired — submitted through a veterinarian.Current test catalog and fees ↗Test catalog specimen requirements ↗August 2026

"Direct Owner Access" is shown only where a laboratory's own current website explicitly describes serving owners. Where it does not, this directory says "Veterinary submission / confirm with laboratory."

Laboratory policies, fees and specimen requirements change. This directory is reviewed periodically and was last verified in August 2026. Always confirm current information directly with the laboratory.

24Which Tests Might Be Relevant?

The Right Test Depends on the Question.

Select what you have observed. This guide produces questions to discuss with your veterinarian — not a list of tests your dog needs, and not a diagnosis. Every prompt is drawn from a curated knowledge base and carries the source that supports it.

Select What You Have Observed

This produces questions to discuss with your veterinarian. It does not produce a diagnosis, and it does not tell you which tests your dog needs.

Questions to Discuss With Your Veterinarian

Select one or more observations above. Every prompt shown is tied to a specific veterinary guideline, peer-reviewed study or veterinary academic source, which you can inspect.

A Single Low T4 Does Not Diagnose Hypothyroidism.

AAHA states that canine hypothyroidism is commonly overdiagnosed, because clinical signs are nonspecific and thyroid testing can be difficult to interpret. Illness, breed, age and medications can all affect thyroid hormone concentrations. AAHA specifically notes that drugs including prednisone and phenobarbital can affect thyroid testing, and that nonthyroidal illness can produce values that mimic hypothyroidism.

Where the clinical picture supports it, additional testing may include total T4, free T4, canine TSH and — in selected cases — thyroid autoantibodies. AAHA notes that free T4 and TSH can help evaluate suspected hypothyroidism when total T4 is low or borderline.

AAHA — Diagnostic Testing and MonitoringAAHA — Categorical Approach to Diagnosis

A Low Resting Cortisol Does Not Diagnose Addison's Disease.

Hypoadrenocorticism can present with vague, fluctuating signs: lethargy, reduced appetite, weight loss, vomiting, diarrhea, weakness, increased thirst and urination, and collapse. The Merck Veterinary Manual describes these signs as variable and nonspecific.

A Common Diagnostic Pathway

  1. CBC, chemistry and electrolytes
  2. Resting cortisol may be used as a screening test
  3. If indicated, an ACTH stimulation test to confirm

AAHA states that if a resting cortisol is below the relevant threshold in a dog suspected of hypoadrenocorticism, an ACTH stimulation test should be used to confirm the diagnosis.

Merck Veterinary Manual — Addison Disease in AnimalsAAHA — 2023 Selected Endocrinopathies Guidelines (PDF)Cornell — Canine Adrenal and Pituitary Function Tests
25Overlapping Presentations

Some Conditions Can Look Like Something Else.

Some endocrine diseases are challenging to diagnose because their signs overlap with many other conditions. That is a statement about diagnostic difficulty — not a claim that any particular disease is routinely missed.

This distinction matters. Where evidence supports a specific statement, we make it and cite it. Where it does not, we describe the overlap instead.

26Seizures & Epilepsy

Could Hormones Be Related to Seizures?

There is a research signal — but no definitive answer.

Researchers have investigated whether sex hormones and sterilization status influence canine epilepsy, but the evidence remains incomplete and inconsistent. A 2014 review concluded that there was insufficient robust research to draw reliable conclusions about the effect of sterilization on epilepsy in dogs.

2014 Review — Sterilization and Canine Epilepsy

Study 1

A large study of dogs with idiopathic epilepsy found an association between neuter status and cluster seizures. Later research did not consistently reproduce this association.

PubMed — View Study

Study 2

A later study of 384 dogs with idiopathic epilepsy found no association between sex, neuter status, body size and cluster seizures.

PubMed — View Study

Study 3

A study of Labrador Retrievers and Border Collies found that neuter status was not associated with age at seizure onset or with cluster seizures.

PubMed — View Study

Study 4

Another large canine study found neutering associated with an increased risk of epilepsy. This was an observational association and cannot establish causation.

PubMed — View Study

Hormones & Seizures

Sex hormones can influence neuronal excitability in humans, and researchers have investigated hormonal effects in dogs. In intact female dogs with idiopathic epilepsy, one study found that some seizure onsets occurred around estrus and diestrus.

These findings do not establish that removing sex hormones causes epilepsy, nor do they establish that testosterone replacement treats epilepsy.

Seizure Onset Around Estrus and Diestrus (2014)

Testosterone and Epilepsy

Current evidence is not sufficient to recommend testosterone therapy as a treatment for canine epilepsy.

The 2025 testosterone safety study included a dog with suspected idiopathic epilepsy that experienced two seizures during the study. This does not imply that testosterone caused the seizures. The event illustrates why neurological history and appropriate monitoring matter when studying hormone restoration.

2025 Testosterone Safety Study

Seizures Are Not Always Epilepsy.

A seizure is a clinical event. Epilepsy is a diagnosis involving recurrent seizures under defined circumstances. Potential metabolic and systemic contributors can include hypoglycemia, electrolyte abnormalities, hepatic dysfunction, toxic exposure, endocrine disease, structural brain disease and other metabolic conditions.

For example, Merck notes that blood glucose should be evaluated in older dogs with periodic weakness, collapse or seizures, because hypoglycemia can be associated with insulinoma and other disorders.

Merck Veterinary Manual — Islet Cell Tumors in Dogs and Cats

If a Dog Has Seizures — Questions to Discuss

  • Could metabolic or endocrine abnormalities be contributing to the seizures?
  • Has blood glucose been evaluated?
  • Have electrolytes and calcium been evaluated?
  • Are liver and kidney function being assessed?
  • Could medication effects be relevant?
  • Based on age at seizure onset and the neurological examination, is advanced neurologic investigation appropriate?
  • Is this consistent with idiopathic epilepsy, or are there features suggesting another cause?

These are questions, not conclusions. This website does not offer a diagnostic conclusion about any individual dog.

Our Final Position on This Question

Research has explored relationships between sex hormones, neutering and canine epilepsy. Some observational studies have reported associations, while other studies have found no significant association. Current evidence is insufficient to conclude that early neutering causes epilepsy or that hormone replacement prevents or treats epilepsy.

This is how this website handles controversial or incomplete evidence: present the signal, present the contradictory evidence, and explain the uncertainty.

2014 Review2016 Study (384 Dogs)2019 Breed Study2017 Cohort Study
27Hormone Testing After Neutering

What About Testing a Neutered Dog's Hormones?

A neutered male dog will normally have dramatically different gonadal hormone concentrations from an intact male. A low testosterone result in a castrated male is therefore expected, and does not by itself prove that the dog has a pathological endocrine disorder.

The purpose of hormone testing must be defined before it is ordered. Not every neutered dog needs a testosterone panel, and this website does not suggest otherwise.

Reasons a Veterinarian Might Consider Hormone Testing

  • Evaluating suspected endocrine disease.
  • Investigating unusual clinical signs.
  • Monitoring an established hormone therapy.
  • Evaluating suspected residual gonadal tissue.
  • Participating in research.
  • Investigating a specific reproductive or endocrine question.

Testosterone Testing

For a neutered male dog, testosterone can be measured, but interpretation depends heavily on timing, assay, laboratory reference range, medications, any hormone therapy and the broader clinical context.

Research has shown that basal testosterone can be useful in assessing neuter status in male dogs — a specific, defined clinical question rather than a general screen.

Basal Testosterone and Neuter Status in Male Dogs

If a Dog Is Receiving Hormone Therapy

Testing should be coordinated with the veterinarian, because timing relative to administration can materially affect interpretation. This website does not provide dosing or injection instructions, and hormone restoration is not an established veterinary therapy.

Hormone Test Directory

A reference for understanding which clinical questions map to which categories of testing — and why.

Clinical QuestionPossible Testing to DiscussWhySource
Suspected hypothyroidismTT4, fT4, canine TSHEvaluate thyroid function; multiple parameters are needed because a single low TT4 is not diagnostic.AAHA↗
Suspected Addison's diseaseElectrolytes, resting cortisol, ACTH stimulation testEvaluate adrenal function; a low resting cortisol is a screening result that requires confirmation.AAHA↗Merck Veterinary Manual↗
Suspected Cushing's diseaseAppropriate cortisol dynamic testingEvaluate hyperadrenocorticism; test selection depends on the clinical presentation.AAHA↗Cornell AHDC↗
Suspected sex-hormone issueTestosterone, estradiol or other targeted assaysDepends entirely on the clinical question being asked, including suspected residual gonadal tissue.PubMed↗UC Davis↗
Monitoring an established hormone therapyTargeted hormone measurement plus safety monitoringDepends on the treatment; timing relative to administration materially affects interpretation.PubMed↗
Weakness or collapseCBC, chemistry, electrolytes, glucose, with endocrine tests where indicatedBroad differential; baseline data narrows the question before specialized assays.AAHA↗Merck Veterinary Manual↗
SeizuresGlucose, electrolytes, liver and kidney assessment, with further testing where indicatedIdentify metabolic or systemic contributors before assuming idiopathic epilepsy.Merck Veterinary Manual↗PubMed↗

These are examples of diagnostic discussions, not universal testing protocols. Your veterinarian determines which tests are appropriate.

28Testing Judgment

More Tests Aren't Always Better.

Endocrine testing can produce misleading results when performed without a clear clinical question. Illness, medications, breed, timing and assay methodology can all influence hormone concentrations.

AAHA specifically notes this problem with thyroid testing, and advises against diagnosing hypothyroidism from an isolated low total T4.

AAHA — Diagnostic Testing and Monitoring

Medication Interference

Tell your veterinarian every medication and supplement your dog receives.

For thyroid testing, AAHA notes that medications such as glucocorticoids and phenobarbital can affect thyroid hormone concentrations, and that nonthyroidal illness can produce values that mimic hypothyroidism.

Never stop a prescribed medication solely to alter laboratory results unless directed by your veterinarian.

AAHA — Categorical Approach to Diagnosis

A Correlation Is a Reason to Investigate — Not a Diagnosis

A study may identify an association between neutering and a health condition without proving that neutering caused the condition. The same principle applies to hormone levels, seizures, thyroid disease, adrenal disease and every other condition discussed on this website.

Critical Disclaimer — Testing Section

Laboratory testing should be guided by a veterinary clinical question.

This website helps owners understand diagnostic options and prepare for conversations with their veterinarian. It does not diagnose disease, prescribe tests, interpret individual laboratory results, or replace veterinary examination.

A laboratory result outside a reference interval does not necessarily mean a dog has a disease, and a result inside the reference interval does not always exclude disease.

When the Answer Doesn't Make Sense

This is about better clinical communication, not confrontation. If findings do not seem to fit your dog, these are reasonable things to ask.

  • Could another condition explain these findings?
  • Are there medications that could be affecting the test results?
  • Should the test be repeated or confirmed using another method?
  • Would consultation with a veterinary internal medicine specialist or endocrinologist be appropriate?
  • Would a veterinary neurologist be appropriate for seizure-related concerns?
29Understand Your Dog's Situation

Context, Not a Diagnosis.

This is deliberately not a risk calculator. There is no validated published model that can convert a dog's details into a disease probability, so this section does not pretend otherwise. It shows you which research is relevant to a dog like yours — and helps you generate questions for your veterinarian.

How It Works

Enter what you know about your dog and select any current concerns. The tool returns relevant research, diagnostic topics to discuss, and three to eight questions for your veterinarian.

Reliability Rule

Every prompt comes from a curated medical knowledge base. No language model invents diagnostic associations here. Each prompt maps to a specific veterinary guideline, peer-reviewed study or veterinary academic source, stored alongside it.

Source Confidence

Select "Why Am I Seeing This?" on any prompt to read why it appeared and open the supporting source. Nothing here recommends tests, and nothing here is a diagnosis.

Generate Questions for Your Veterinarian

Current Health Concerns (Select Any That Apply)

Educational Prompts

Enter what you know about your dog. This tool then shows the research that is relevant to a dog like yours, the diagnostic topics worth discussing, and questions you can bring to your veterinarian. No risk score, no probability, no diagnosis. Every prompt is drawn from a curated set tied to a specific source, which you can inspect.

If your dog is already neutered and you have reported signs such as weakness or muscle loss, the prompts will note that these signs are nonspecific and may have many causes, and that you could ask your veterinarian whether a metabolic or endocrine evaluation is appropriate and whether hormone testing has a legitimate clinical purpose in your particular situation. That is not a suggestion of testosterone deficiency, and it is not a recommendation of hormone therapy — see Hormone Restoration for what that research does and does not show.

30Talk to Your Veterinarian

Bring the Research Into the Exam Room.

The purpose of this website is not to replace veterinary care, and it is certainly not to position owners against their veterinarians. It is to make the appointment more productive.

If your dog has already been sterilized, these questions are a reasonable place to start.

  • 01Could my dog's breed and age at sterilization be relevant to his or her current health?
  • 02Are there orthopedic issues we should monitor?
  • 03Is my dog's body composition appropriate?
  • 04Are there clinical signs that warrant further investigation?
  • 05Would laboratory testing be appropriate?
  • 06Would an endocrinology consultation be useful?
  • 07Is hormone therapy currently supported by evidence for my dog's specific situation?
  • 08If not, are there clinical trials or emerging research I should know about?
31Evidence Library

Follow the Evidence.

Every substantive claim on this page traces back to one of these sources. Where a claim could not be sourced to veterinary guidelines, peer-reviewed research or a veterinary academic institution, it is not on this page.

American Animal Hospital Association

University of California, Davis

World Small Animal Veterinary Association

Peer-Reviewed Research — Gonad-Sparing Sterilization

Peer-Reviewed Research — Hormone Restoration

Veterinary Endocrine Guidelines & References — Testing

Veterinary Diagnostic Laboratories

Peer-Reviewed Research — Seizures, Epilepsy & Hormones

For the hormone-restoration sections, we link to the underlying peer-reviewed literature rather than secondary coverage. Publication databases occasionally reorganize record URLs; the linked searches resolve to the primary publications.

About This Resource

Canine Hormone Health explores an emerging question in veterinary medicine: if reproductive hormones influence health beyond reproduction, can future medicine develop better ways to understand and manage the consequences of their loss?

That is a question, not a claim. Hormone replacement is not an established veterinary therapy, and this site does not present it as one.